Convert to new assembler field syntax.

[FreeBSD/FreeBSD.git] / sys / dev / aic7xxx / aic79xx.seq

/*
 * Adaptec 274x/284x/294x device driver firmware for Linux and FreeBSD.
 *
 * Copyright (c) 1994-2001 Justin T. Gibbs.
 * Copyright (c) 2000-2001 Adaptec Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce at minimum a disclaimer
 *    substantially similar to the "NO WARRANTY" disclaimer below
 *    ("Disclaimer") and any redistribution must be conditioned upon
 *    including a substantially similar Disclaimer requirement for further
 *    binary redistribution.
 * 3. Neither the names of the above-listed copyright holders nor the names
 *    of any contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * NO WARRANTY
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGES.
 *
 * $FreeBSD$
 */

VERSION = "$Id: //depot/aic7xxx/aic7xxx/aic79xx.seq#42 $"
PATCH_ARG_LIST = "struct ahd_softc *ahd"

#include "aic79xx.reg"
#include "scsi_message.h"

idle_loop:
        SET_MODE(M_SCSI, M_SCSI);
        test    SCSISEQ0, ENSELO|ENARBO jnz idle_loop_checkbus;
        test    SEQ_FLAGS2, SELECTOUT_QFROZEN jnz idle_loop_checkbus;
        cmp     WAITING_TID_HEAD[1], SCB_LIST_NULL je idle_loop_checkbus;
        /*
         * ENSELO is cleared by a SELDO, so we must test for SELDO
         * one last time.
         */
BEGIN_CRITICAL;
        test    SSTAT0, SELDO jnz select_out;
END_CRITICAL;
        call    start_selection;
idle_loop_checkbus:
BEGIN_CRITICAL;
        test    SSTAT0, SELDO jnz select_out;
END_CRITICAL;
        test    SSTAT0, SELDI jnz select_in;
        test    SCSIPHASE, ~DATA_PHASE_MASK jz idle_loop_check_nonpackreq;
        test    SCSISIGO, ATNO jz idle_loop_check_nonpackreq;
        call    unexpected_nonpkt_phase_find_ctxt;
idle_loop_check_nonpackreq:
        test    SSTAT2, NONPACKREQ jz idle_loop_scsi;
        call    unexpected_nonpkt_phase_find_ctxt;
idle_loop_scsi:
BEGIN_CRITICAL;
        test    LQISTAT2, LQIGSAVAIL jz idle_loop_service_fifos;
        /*
         * We have received good status for this transaction.  There may
         * still be data in our FIFOs draining to the host.  Setup
         * monitoring of the draining process or complete the SCB.
         */
good_status_IU_done:
        bmov    SCBPTR, GSFIFO, 2;
        clr     SCB_SCSI_STATUS;
        or      SCB_CONTROL, STATUS_RCVD;

        /*
         * Since this status did not consume a FIFO, we have to
         * be a bit more dilligent in how we check for FIFOs pertaining
         * to this transaction.  There are three states that a FIFO still
         * transferring data may be in.
         *
         * 1) Configured and draining to the host, with a pending CLRCHN.
         * 2) Configured and draining to the host, no pending CLRCHN.
         * 3) Pending cfg4data, fifo not empty.
         *
         * For case 1, we assume that our DMA post of the completed command
         * will occur after the FIFO finishes draining due to the higher
         * priority of data FIFO transfers relative to command channel
         * transfers.
         *
         * Case 2 can be detected by noticing that a longjmp is active for the
         * FIFO and LONGJMP_SCB matches our SCB.  In this case, we allow
         * the routine servicing the FIFO to complete the SCB.
         * 
         * Case 3 implies either a pending or yet to occur save data
         * pointers for this same context in the other FIFO.  So, if
         * we detect case 2, we will properly defer the post of the SCB
         * and achieve the desired result.  The pending cfg4data will
         * notice that status has been received and complete the SCB.
         */
        test    SCB_SGPTR, SG_LIST_NULL jz good_status_check_fifos;
        /*
         * All segments have been loaded (or no data transfer), so
         * it is safe to complete the command.  Since this was a
         * cheap command to check for completion, loop to see if
         * more entries can be removed from the GSFIFO.
         */
        call    complete;
END_CRITICAL;
        jmp     idle_loop_scsi;
BEGIN_CRITICAL;
good_status_check_fifos:
        clc;
        bmov    ARG_1, SCBPTR, 2;
        SET_MODE(M_DFF0, M_DFF0);
        call    check_fifo;
        jc      idle_loop_service_fifos;
        SET_MODE(M_DFF1, M_DFF1);
        call    check_fifo;
        jc      idle_loop_service_fifos;
        SET_MODE(M_SCSI, M_SCSI);
        call    queue_scb_completion;
END_CRITICAL;
idle_loop_service_fifos:
        SET_MODE(M_DFF0, M_DFF0);
        test    LONGJMP_ADDR[1], INVALID_ADDR jnz idle_loop_next_fifo;
        call    longjmp;
idle_loop_next_fifo:
        SET_MODE(M_DFF1, M_DFF1);
        test    LONGJMP_ADDR[1], INVALID_ADDR jnz idle_loop_last_fifo_done;
        call    longjmp;
idle_loop_last_fifo_done:
        call    idle_loop_cchan;
        jmp     idle_loop;

idle_loop_cchan:
        SET_MODE(M_CCHAN, M_CCHAN);
        test    CCSCBCTL, CCARREN|CCSCBEN jz scbdma_idle;
        test    CCSCBCTL, CCSCBDIR jnz fetch_new_scb_inprog;
        test    CCSCBCTL, CCSCBDONE jz return;
        /* FALLTHROUGH */
scbdma_tohost_done:
        test    CCSCBCTL, CCARREN jz fill_qoutfifo_dmadone;
        /*
         * A complete SCB upload requires no intervention.
         * The SCB is already on the COMPLETE_SCB list
         * and its completion notification will now be
         * handled just like any other SCB.
         */
        and     CCSCBCTL, ~(CCARREN|CCSCBEN) ret;
fill_qoutfifo_dmadone:
        and     CCSCBCTL, ~(CCARREN|CCSCBEN);
        mvi     INTSTAT, CMDCMPLT;
        mvi     COMPLETE_SCB_DMAINPROG_HEAD[1], SCB_LIST_NULL;
        bmov    QOUTFIFO_NEXT_ADDR, SCBHADDR, 4;
        test    QOFF_CTLSTA, SDSCB_ROLLOVR jz return;
        bmov    QOUTFIFO_NEXT_ADDR, SHARED_DATA_ADDR, 4 ret;

fetch_new_scb_inprog:
        test    CCSCBCTL, ARRDONE jz return;
fetch_new_scb_done:
        and     CCSCBCTL, ~(CCARREN|CCSCBEN);
        bmov    REG0, SCBPTR, 2;
        /* Update the next SCB address to download. */
        bmov    NEXT_QUEUED_SCB_ADDR, SCB_NEXT_SCB_BUSADDR, 4;
        mvi     SCB_NEXT[1], SCB_LIST_NULL;
        mvi     SCB_NEXT2[1], SCB_LIST_NULL;
        /*
         * SCBs that want to send messages are always
         * queued independently.  This ensures that they
         * are at the head of the SCB list to select out
         * to a target and we will see the MK_MESSAGE flag.
         */
        test    SCB_CONTROL, MK_MESSAGE jnz first_new_target_scb;
        shr     SINDEX, 3, SCB_SCSIID;
        and     SINDEX, ~0x1;
        mvi     SINDEX[1], (WAITING_SCB_TAILS >> 8);
        bmov    DINDEX, SINDEX, 2;
        bmov    SCBPTR, SINDIR, 2;
        bmov    DINDIR, REG0, 2;
        cmp     SCBPTR[1], SCB_LIST_NULL je first_new_target_scb;
        bmov    SCB_NEXT, REG0, 2;
fetch_new_scb_fini:
        /* Increment our position in the QINFIFO. */
        mov     NONE, SNSCB_QOFF ret;
first_new_target_scb:
        cmp     WAITING_TID_HEAD[1], SCB_LIST_NULL je first_new_scb;
        bmov    SCBPTR, WAITING_TID_TAIL, 2;
        bmov    SCB_NEXT2, REG0, 2;
        bmov    WAITING_TID_TAIL, REG0, 2;
        /* Increment our position in the QINFIFO. */
        mov     NONE, SNSCB_QOFF ret;
first_new_scb:
        bmov    WAITING_TID_HEAD, REG0, 2;
        bmov    WAITING_TID_TAIL, REG0, 2;
        /* Increment our position in the QINFIFO. */
        mov     NONE, SNSCB_QOFF ret;

scbdma_idle:
        /*
         * Give precedence to downloading new SCBs to execute
         * unless select-outs are currently frozen.
         * XXX Use a timer to prevent completion starvation.
         */
        test    SEQ_FLAGS2, SELECTOUT_QFROZEN jnz . + 2;
BEGIN_CRITICAL;
        test    QOFF_CTLSTA, NEW_SCB_AVAIL jnz fetch_new_scb;
        cmp     COMPLETE_DMA_SCB_HEAD[1], SCB_LIST_NULL jne dma_complete_scb;
        cmp     COMPLETE_SCB_HEAD[1], SCB_LIST_NULL je return;
        /* FALLTHROUGH */
fill_qoutfifo:
        /*
         * Keep track of the SCBs we are dmaing just
         * in case the DMA fails or is aborted.
         */
        bmov    COMPLETE_SCB_DMAINPROG_HEAD, COMPLETE_SCB_HEAD, 2;
        mvi     CCSCBCTL, CCSCBRESET;
        bmov    SCBHADDR, QOUTFIFO_NEXT_ADDR, 4;
        bmov    CCSCBRAM, COMPLETE_SCB_HEAD, 2;
        bmov    SCBPTR, COMPLETE_SCB_HEAD, 2;
        jmp     fill_qoutfifo_first_entry;
fill_qoutfifo_loop:
        bmov    CCSCBRAM, SCB_NEXT_COMPLETE, 2;
        bmov    SCBPTR, SCB_NEXT_COMPLETE, 2;
fill_qoutfifo_first_entry:
        mov     NONE, SDSCB_QOFF;
        cmp     SCB_NEXT_COMPLETE[1], SCB_LIST_NULL je fill_qoutfifo_done;
        cmp     CCSCBADDR, CCSCBADDR_MAX je fill_qoutfifo_done;
        test    QOFF_CTLSTA, SDSCB_ROLLOVR jz fill_qoutfifo_loop;
fill_qoutfifo_done:
        mov     SCBHCNT, CCSCBADDR;
        mvi     CCSCBCTL, CCSCBEN|CCSCBRESET;
        bmov    COMPLETE_SCB_HEAD, SCB_NEXT_COMPLETE, 2;
        mvi     SCB_NEXT_COMPLETE[1], SCB_LIST_NULL ret;

fetch_new_scb:
        bmov    SCBHADDR, NEXT_QUEUED_SCB_ADDR, 4;
        mvi     CCARREN|CCSCBEN|CCSCBDIR|CCSCBRESET jmp dma_scb;
dma_complete_scb:
        bmov    SCBPTR, COMPLETE_DMA_SCB_HEAD, 2;
        bmov    SCBHADDR, SCB_BUSADDR, 4;
        mvi     CCARREN|CCSCBEN|CCSCBRESET call dma_scb;
        /*
         * Now that we've started the DMA, push us onto
         * the normal completion queue to have our SCBID
         * posted to the kernel.
         */
        bmov    COMPLETE_DMA_SCB_HEAD, SCB_NEXT_COMPLETE, 2;
        bmov    SCB_NEXT_COMPLETE, COMPLETE_SCB_HEAD, 2;
        bmov    COMPLETE_SCB_HEAD, SCBPTR, 2 ret;
END_CRITICAL;

/*
 * Either post or fetch an SCB from host memory.  The caller
 * is responsible for polling for transfer completion.
 *
 * Prerequisits: Mode == M_CCHAN
 *               SINDEX contains CCSCBCTL flags
 *               SCBHADDR set to Host SCB address
 *               SCBPTR set to SCB src location on "push" operations
 */
SET_SRC_MODE    M_CCHAN;
SET_DST_MODE    M_CCHAN;
dma_scb:
        mvi     SCBHCNT, SCB_TRANSFER_SIZE;
        mov     CCSCBCTL, SINDEX;
        or      SEQ_FLAGS2, SCB_DMA ret;

BEGIN_CRITICAL;
setjmp_setscb:
        bmov    LONGJMP_SCB, SCBPTR, 2;
setjmp:
        bmov    LONGJMP_ADDR, STACK, 2 ret;
setjmp_inline:
        bmov    LONGJMP_ADDR, STACK, 2;
longjmp:
        bmov    STACK, LONGJMP_ADDR, 2 ret;
END_CRITICAL;

/************************ Packetized LongJmp Routines *************************/
/*
 * Must disable interrupts when setting the mode pointer
 * register as an interrupt occurring mid update will
 * fail to store the new mode value for restoration on
 * an iret.
 */
set_mode_work_around:
        mvi     SEQINTCTL, INTVEC1DSL;
        mov     MODE_PTR, SINDEX;
        clr     SEQINTCTL ret;

SET_SRC_MODE    M_SCSI;
SET_DST_MODE    M_SCSI;
start_selection:
BEGIN_CRITICAL;
        if ((ahd->bugs & AHD_SENT_SCB_UPDATE_BUG) != 0) {
                /*
                 * Razor #494
                 * Rev A hardware fails to update LAST/CURR/NEXTSCB
                 * correctly after a packetized selection in several
                 * situations:
                 *
                 * 1) If only one command existed in the the queue, the
                 *    LAST/CURR/NEXTSCB are unchanged.
                 *
                 * 2) In a non QAS, protocol allowed phase change,
                 *    the queue is shifted 1 too far.  LASTSCB is
                 *    the last SCB that was correctly processed.
                 * 
                 * 3) In the QAS case, if the full list of commands
                 *    was successfully sent, NEXTSCB is NULL and neither
                 *    CURRSCB nor LASTSCB can be trusted.  We must
                 *    manually walk the list counting MAXCMDCNT elements
                 *    to find the last SCB that was sent correctly.
                 *
                 * To simplify the workaround for this bug in SELDO
                 * handling, we initialize LASTSCB prior to enabling
                 * selection so we can rely on it even for case #1 above.
                 */
                bmov    LASTSCB, WAITING_TID_HEAD, 2;
        }
        bmov    CURRSCB, WAITING_TID_HEAD, 2;
        bmov    SCBPTR, WAITING_TID_HEAD, 2;
        shr     SELOID, 4, SCB_SCSIID;
        /*
         * If we want to send a message to the device, ensure
         * we are selecting with atn irregardless of our packetized
         * agreement.  Since SPI4 only allows target reset or PPR
         * messages if this is a packetized connection, the change
         * to our negotiation table entry for this selection will
         * be cleared when the message is acted on.
         */
        test    SCB_CONTROL, MK_MESSAGE jz . + 3;
        mov     NEGOADDR, SELOID;
        or      NEGCONOPTS, ENAUTOATNO;
        or      SCSISEQ0, ENSELO ret;
END_CRITICAL;

/*
 * Allocate a FIFO for a non-packetized transaction.
 * For some reason unkown to me, both FIFOs must be free before we
 * can allocate a FIFO for a non-packetized transaction.  This
 * may be fixed in Rev B.
 */
allocate_fifo_loop:
        /*
         * Do whatever work is required to free a FIFO.
         */
        SET_MODE(M_DFF0, M_DFF0);
        test    LONGJMP_ADDR[1], INVALID_ADDR jnz . + 2;
        call    longjmp;
        SET_MODE(M_DFF1, M_DFF1);
        test    LONGJMP_ADDR[1], INVALID_ADDR jnz . + 2;
        call    longjmp;
        SET_MODE(M_SCSI, M_SCSI);
allocate_fifo:
        and     A, FIFO0FREE|FIFO1FREE, DFFSTAT;
        cmp     A, FIFO0FREE|FIFO1FREE jne allocate_fifo_loop;
take_fifo:
        bmov    ARG_1, SCBPTR, 2;
        or      DFFSTAT, CURRFIFO;
        SET_MODE(M_DFF1, M_DFF1);
        bmov    SCBPTR, ARG_1, 2 ret;

/*
 * We have been reselected as an initiator
 * or selected as a target.
 */
SET_SRC_MODE    M_SCSI;
SET_DST_MODE    M_SCSI;
select_in:
        or      SXFRCTL0, SPIOEN;
        and     SAVED_SCSIID, SELID_MASK, SELID;
        and     A, OID, IOWNID;
        or      SAVED_SCSIID, A;
        mvi     CLRSINT0, CLRSELDI;
        jmp     ITloop;

/*
 * We have successfully selected out.
 *
 * Clear SELDO.
 * Dequeue all SCBs sent from the waiting queue
 * Requeue all SCBs *not* sent to the tail of the waiting queue
 * Take Razor #494 into account for above.
 *
 * In Packetized Mode:
 *      Return to the idle loop.  Our interrupt handler will take
 *      care of any incoming L_Qs.
 *
 * In Non-Packetize Mode:
 *      Continue to our normal state machine.
 */
SET_SRC_MODE    M_SCSI;
SET_DST_MODE    M_SCSI;
select_out:
BEGIN_CRITICAL;
        /* Clear out all SCBs that have been successfully sent. */
        if ((ahd->bugs & AHD_SENT_SCB_UPDATE_BUG) != 0) {
                /*
                 * For packetized, the LQO manager clears ENSELO on
                 * the assertion of SELDO.  If we are non-packetized,
                 * LASTSCB and CURRSCB are acuate.
                 */
                test    SCSISEQ0, ENSELO jnz use_lastscb;

                /*
                 * The update is correct for LQOSTAT1 errors.  All
                 * but LQOBUSFREE are handled by kernel interrupts.
                 * If we see LQOBUSFREE, return to the idle loop.
                 * Once we are out of the select_out critical section,
                 * the kernel will cleanup the LQOBUSFREE and we will
                 * eventually restart the selection if appropriate.
                 */
                test    LQOSTAT1, LQOBUSFREE jnz idle_loop;

                /*
                 * On a phase change oustside of packet boundaries,
                 * LASTSCB points to the currently active SCB context
                 * on the bus.
                 */
                test    LQOSTAT2, LQOPHACHGOUTPKT jnz use_lastscb;

                /*
                 * If the hardware has traversed the whole list, NEXTSCB
                 * will be NULL, CURRSCB and LASTSCB cannot be trusted,
                 * but MAXCMDCNT is accurate.  If we stop part way through
                 * the list or only had one command to issue, NEXTSCB[1] is
                 * not NULL and LASTSCB is the last command to go out.
                 */
                cmp     NEXTSCB[1], SCB_LIST_NULL jne use_lastscb;

                /*
                 * Brute force walk.
                 */
                bmov    SCBPTR, WAITING_TID_HEAD, 2;
                mvi     SEQINTCTL, INTVEC1DSL;
                mvi     MODE_PTR, MK_MODE(M_CFG, M_CFG);
                mov     A, MAXCMDCNT;
                mvi     MODE_PTR, MK_MODE(M_SCSI, M_SCSI);
                clr     SEQINTCTL;
find_lastscb_loop:
                dec     A;
                test    A, 0xFF jz found_last_sent_scb;
                bmov    SCBPTR, SCB_NEXT, 2;
                jmp     find_lastscb_loop;
use_lastscb:
                bmov    SCBPTR, LASTSCB, 2;
found_last_sent_scb:
                bmov    CURRSCB, SCBPTR, 2;
curscb_ww_done:
        } else {
                /*
                 * Untested - Verify with Rev B.
                 */
                bmov    SCBPTR, CURRSCB, 2;
        }
        /*
         * Requeue any SCBs not sent, to the tail of the waiting Q.
         */
        cmp     SCB_NEXT[1], SCB_LIST_NULL je select_out_list_done;

        /*
         * We know that neither the per-TID list nor the list of
         * TIDs is empty.  Use this knowledge to our advantage.
         */
        bmov    REG0, SCB_NEXT, 2;
        bmov    SCBPTR, WAITING_TID_TAIL, 2;
        bmov    SCB_NEXT2, REG0, 2;
        bmov    WAITING_TID_TAIL, REG0, 2;
        jmp     select_out_inc_tid_q;

select_out_list_done:
        /*
         * The whole list made it.  Just clear our TID's tail pointer
         * unless we were queued independently due to our need to
         * send a message.
         */
        test    SCB_CONTROL, MK_MESSAGE jnz select_out_inc_tid_q;
        shr     DINDEX, 3, SCB_SCSIID;
/* XXX When we switch to SCB_SELOID, put +1 in addition below. */
        or      DINDEX, 1;      /* Want only the second byte */
        mvi     DINDEX[1], ((WAITING_SCB_TAILS) >> 8);
        mvi     DINDIR, SCB_LIST_NULL;
select_out_inc_tid_q:
        bmov    SCBPTR, WAITING_TID_HEAD, 2;
        bmov    WAITING_TID_HEAD, SCB_NEXT2, 2;
        cmp     WAITING_TID_HEAD[1], SCB_LIST_NULL jne . + 2;
        mvi     WAITING_TID_TAIL[1], SCB_LIST_NULL;
        bmov    SCBPTR, CURRSCB, 2;
END_CRITICAL;

        mvi     CLRSINT0, CLRSELDO;

        test    LQOSTAT2, LQOPHACHGOUTPKT jnz unexpected_nonpkt_phase;
        test    LQOSTAT1, LQOPHACHGINPKT jnz unexpected_nonpkt_phase;

        /*
         * If this is a packetized connection, return to our
         * idle_loop and let our interrupt handler deal with
         * any connection setup/teardown issues.  The only
         * exception is the case of MK_MESSAGE SCBs.  In the
         * A, the LQO manager transitions to LQOSTOP0 even if
         * we have selected out with ATN asserted and the target
         * REQs in a non-packet phase.
         */
        if ((ahd->bugs & AHD_LQO_ATNO_BUG) != 0) {
                test    SCB_CONTROL, MK_MESSAGE jz select_out_no_message;
                test    SCSISIGO, ATNO jnz select_out_non_packetized;
select_out_no_message:
        }
        test    LQOSTAT2, LQOSTOP0 jnz idle_loop;

select_out_non_packetized:
        /* Non packetized request. */
        and     SCSISEQ0, ~ENSELO;
        mov     SAVED_SCSIID, SCB_SCSIID;
        mov     SAVED_LUN, SCB_LUN;
        or      SXFRCTL0, SPIOEN;

        /*
         * As soon as we get a successful selection, the target
         * should go into the message out phase since we have ATN
         * asserted.
         */
        mvi     MSG_OUT, MSG_IDENTIFYFLAG;
        mvi     SEQ_FLAGS, NO_CDB_SENT;

        /*
         * Main loop for information transfer phases.  Wait for the
         * target to assert REQ before checking MSG, C/D and I/O for
         * the bus phase.
         */
mesgin_phasemis:
ITloop:
        call    phase_lock;

        mov     A, LASTPHASE;

        test    A, ~P_DATAIN_DT jz p_data;
        cmp     A,P_COMMAND     je p_command;
        cmp     A,P_MESGOUT     je p_mesgout;
        cmp     A,P_STATUS      je p_status;
        cmp     A,P_MESGIN      je p_mesgin;

        mvi     SEQINTCODE, BAD_PHASE;
        jmp     ITloop;                 /* Try reading the bus again. */

/*
 * Command phase.  Set up the DMA registers and let 'er rip.
 */
p_command:
SET_SRC_MODE    M_DFF1;
SET_DST_MODE    M_DFF1;
        test    MODE_PTR, ~(MK_MODE(M_DFF1, M_DFF1))
                jnz p_command_allocate_fifo;
        /*
         * Command retry.  Free our current FIFO and
         * re-allocate a FIFO so transfer state is
         * reset.
         */
        mvi     DFFSXFRCTL, RSTCHN|CLRSHCNT;
p_command_allocate_fifo:
        call    allocate_fifo;
        add     NONE, -17, SCB_CDB_LEN;
        jnc     p_command_embedded;
p_command_from_host:
        bmov    HADDR[0], SCB_CDB_PTR, 11;
        mvi     SG_CACHE_PRE, LAST_SEG;
        mvi     DFCNTRL, (PRELOADEN|SCSIEN|HDMAEN);
        jmp     p_command_loop;
p_command_embedded:
        bmov    SHCNT[0], SCB_CDB_LEN,  1;
        bmov    SHCNT[1], ALLZEROS, 2;
        bmov    DFDAT, SCB_CDB_STORE, 16; 
        mvi     DFCNTRL, SCSIEN;
p_command_loop:
        test    DFCNTRL, SCSIEN jnz p_command_loop;
        /*
         * DMA Channel automatically disabled.
         * Don't allow a data phase if the command
         * was not fully transferred.  Make sure that
         * we clear the IDENTIFY SEEN flag if a retry
         * falls short too.
         */
        and     SEQ_FLAGS, ~NO_CDB_SENT;
        test    SSTAT2, SDONE jnz ITloop;
        or      SEQ_FLAGS, NO_CDB_SENT;
        jmp     ITloop;


/*
 * Status phase.  Wait for the data byte to appear, then read it
 * and store it into the SCB.
 */
SET_SRC_MODE    M_SCSI;
SET_DST_MODE    M_SCSI;
p_status:
        test    SEQ_FLAGS,NOT_IDENTIFIED jz p_status_okay;
        mvi     SEQINTCODE, PROTO_VIOLATION;
        jmp     mesgin_done;
p_status_okay:
        mov     SCB_SCSI_STATUS, SCSIDAT;
        or      SCB_CONTROL, STATUS_RCVD;
        jmp     ITloop;

/*
 * Message out phase.  If MSG_OUT is MSG_IDENTIFYFLAG, build a full
 * indentify message sequence and send it to the target.  The host may
 * override this behavior by setting the MK_MESSAGE bit in the SCB
 * control byte.  This will cause us to interrupt the host and allow
 * it to handle the message phase completely on its own.  If the bit
 * associated with this target is set, we will also interrupt the host,
 * thereby allowing it to send a message on the next selection regardless
 * of the transaction being sent.
 * 
 * If MSG_OUT is == HOST_MSG, also interrupt the host and take a message.
 * This is done to allow the host to send messages outside of an identify
 * sequence while protecting the seqencer from testing the MK_MESSAGE bit
 * on an SCB that might not be for the current nexus. (For example, a
 * BDR message in responce to a bad reselection would leave us pointed to
 * an SCB that doesn't have anything to do with the current target).
 *
 * Otherwise, treat MSG_OUT as a 1 byte message to send (abort, abort tag,
 * bus device reset).
 *
 * When there are no messages to send, MSG_OUT should be set to MSG_NOOP,
 * in case the target decides to put us in this phase for some strange
 * reason.
 */
p_mesgout_retry:
        /* Turn on ATN for the retry */
        mvi     SCSISIGO, ATNO;
p_mesgout:
        mov     SINDEX, MSG_OUT;
        cmp     SINDEX, MSG_IDENTIFYFLAG jne p_mesgout_from_host;
        test    SCB_CONTROL,MK_MESSAGE  jnz host_message_loop;
p_mesgout_identify:
        or      SINDEX, MSG_IDENTIFYFLAG|DISCENB, SCB_LUN;
        test    SCB_CONTROL, DISCENB jnz . + 2;
        and     SINDEX, ~DISCENB;
/*
 * Send a tag message if TAG_ENB is set in the SCB control block.
 * Use SCB_NONPACKET_TAG as the tag value.
 */
p_mesgout_tag:
        test    SCB_CONTROL,TAG_ENB jz  p_mesgout_onebyte;
        mov     SCSIDAT, SINDEX;        /* Send the identify message */
        call    phase_lock;
        cmp     LASTPHASE, P_MESGOUT    jne p_mesgout_done;
        and     SCSIDAT,TAG_ENB|SCB_TAG_TYPE,SCB_CONTROL;
        call    phase_lock;
        cmp     LASTPHASE, P_MESGOUT    jne p_mesgout_done;
        mov     SCB_NONPACKET_TAG jmp p_mesgout_onebyte;
/*
 * Interrupt the driver, and allow it to handle this message
 * phase and any required retries.
 */
p_mesgout_from_host:
        cmp     SINDEX, HOST_MSG        jne p_mesgout_onebyte;
        jmp     host_message_loop;

p_mesgout_onebyte:
        mvi     CLRSINT1, CLRATNO;
        mov     SCSIDAT, SINDEX;

/*
 * If the next bus phase after ATN drops is message out, it means
 * that the target is requesting that the last message(s) be resent.
 */
        call    phase_lock;
        cmp     LASTPHASE, P_MESGOUT    je p_mesgout_retry;

p_mesgout_done:
        mvi     CLRSINT1,CLRATNO;       /* Be sure to turn ATNO off */
        mov     LAST_MSG, MSG_OUT;
        mvi     MSG_OUT, MSG_NOOP;      /* No message left */
        jmp     ITloop;

/*
 * Message in phase.  Bytes are read using Automatic PIO mode.
 */
p_mesgin:
        /* read the 1st message byte */
        mvi     ACCUM           call inb_first;

        test    A,MSG_IDENTIFYFLAG      jnz mesgin_identify;
        cmp     A,MSG_DISCONNECT        je mesgin_disconnect;
        cmp     A,MSG_SAVEDATAPOINTER   je mesgin_sdptrs;
        cmp     ALLZEROS,A              je mesgin_complete;
        cmp     A,MSG_RESTOREPOINTERS   je mesgin_rdptrs;
        cmp     A,MSG_IGN_WIDE_RESIDUE  je mesgin_ign_wide_residue;
        cmp     A,MSG_NOOP              je mesgin_done;

/*
 * Pushed message loop to allow the kernel to
 * run it's own message state engine.  To avoid an
 * extra nop instruction after signaling the kernel,
 * we perform the phase_lock before checking to see
 * if we should exit the loop and skip the phase_lock
 * in the ITloop.  Performing back to back phase_locks
 * shouldn't hurt, but why do it twice...
 */
host_message_loop:
        call    phase_lock;     /* Benign the first time through. */
        mvi     SEQINTCODE, HOST_MSG_LOOP;
        cmp     RETURN_1, EXIT_MSG_LOOP je ITloop;
        cmp     RETURN_1, CONT_MSG_LOOP_WRITE   jne . + 3;
        mov     SCSIDAT, RETURN_2;
        jmp     host_message_loop;
        /* Must be CONT_MSG_LOOP_READ */
        mov     NONE, SCSIDAT;  /* ACK Byte */
        jmp     host_message_loop;

mesgin_ign_wide_residue:
        shr     NEGOADDR, 4, SAVED_SCSIID;
        test    NEGCONOPTS, WIDEXFER jz mesgin_reject;
        /* Pull the residue byte */
        mvi     REG0    call inb_next;
        cmp     REG0, 0x01 jne mesgin_reject;
        test    SCB_RESIDUAL_SGPTR[0], SG_LIST_NULL jz . + 2;
        test    DATA_COUNT_ODD, 0x1     jz mesgin_done;
        mvi     SEQINTCODE, IGN_WIDE_RES;
        jmp     mesgin_done;

mesgin_reject:
        mvi     MSG_MESSAGE_REJECT      call mk_mesg;
mesgin_done:
        mov     NONE,SCSIDAT;           /*dummy read from latch to ACK*/
        jmp     ITloop;

#define INDEX_DISC_LIST_SCB(target, lun)                                \
        mov     SCBPTR, lun;                                            \
        shr     SCBPTR[1], 3, target
        
#define INDEX_DISC_LIST(target, lun)                                    \
        INDEX_DISC_LIST_SCB(target, lun);                               \
        and     SINDEX, 0x7, target;                                    \
        shl     SINDEX, 1;                                              \
        add     SINDEX, (SCB_DISCONNECTED_LISTS & 0xFF);                \
        mvi     SINDEX[1], ((SCB_DISCONNECTED_LISTS >> 8) & 0xFF)

mesgin_identify:
        /*
         * Determine whether a target is using tagged or non-tagged
         * transactions by first looking at the transaction stored in
         * the per-device, disconnected array.  If there is no untagged
         * transaction for this target this must be an untagged transaction.
         */
        shr     SINDEX, 4, SAVED_SCSIID;
        and     SAVED_LUN, MSG_IDENTIFY_LUNMASK, A;
        INDEX_DISC_LIST(SINDEX, SAVED_LUN);
        bmov    DINDEX, SINDEX, 2;
        bmov    SCBPTR, SINDIR, 2;
        cmp     SCBPTR[1], SCB_LIST_NULL je snoop_tag;
        test    SCB_CONTROL, TAG_ENB jnz snoop_tag;
        /* Untagged.  Setup the SCB. */
        bmov    REG1, SCB_TAG, 4;       /* Save SCB_TAG and SCB_NEXT */
        jmp dequeue_first_scb;

/*
 * Here we "snoop" the bus looking for a SIMPLE QUEUE TAG message.
 * If we get one, we use the tag returned to find the proper
 * SCB.  The disconnected list contains any outstanding tagged transactions
 * where SCB_TAG != SCB_NONPACKET_TAG or SCB_NONPACKET_TAG + 256.
 * After receiving the tag, look for the SCB at SCB locations tag and
 * tag + 256.  If those SCBs do not match, traverse the disconnected
 * list until we find the correct SCB.
 */
snoop_tag:
        if ((ahd->flags & AHD_SEQUENCER_DEBUG) != 0) {
                or      SEQ_FLAGS, 0x80;
        }
        mov     NONE, SCSIDAT;          /* ACK Identify MSG */
        call    phase_lock;
        if ((ahd->flags & AHD_SEQUENCER_DEBUG) != 0) {
                or      SEQ_FLAGS, 0x1;
        }
        cmp     LASTPHASE, P_MESGIN     jne not_found_ITloop;
        if ((ahd->flags & AHD_SEQUENCER_DEBUG) != 0) {
                or      SEQ_FLAGS, 0x2;
        }
        cmp     SCSIBUS, MSG_SIMPLE_Q_TAG jne not_found;
get_tag:
        /* Save diconnected list head. */
        bmov    REG0, SCBPTR, 2;
        clr     SCBPTR[1];
        mvi     SCBPTR  call inb_next;  /* tag value */
        mov     REG1, SCBPTR;
verify_scb:
        mov     A, REG1;
        cmp     SCB_NONPACKET_TAG, A jne verify_other_scb;
        mov     A, SAVED_SCSIID;
        cmp     SCB_SCSIID, A jne verify_other_scb;
        mov     A, SAVED_LUN;
        cmp     SCB_LUN, A je setup_SCB;
verify_other_scb:
        xor     SCBPTR[1], 1;
        test    SCBPTR[1], 0xFF jnz verify_scb;

search_disc_list:
        /* Restore disconnected list head. */
        bmov    SCBPTR, REG0, 2;
        mvi     REG0[1], SCB_LIST_NULL;
        mov     A, REG1;
search_disc_list_loop:
        cmp     SCB_NONPACKET_TAG, A je dequeue_scb;
        bmov    REG0, SCBPTR, 2;
        bmov    SCBPTR, SCB_NEXT, 2;
        cmp     SCBPTR[1], SCB_LIST_NULL jne search_disc_list_loop;
        jmp     not_found;

dequeue_scb:
        bmov    REG1, SCB_TAG, 4;       /* Save SCB_TAG and SCB_NEXT */
        cmp     REG0[1], SCB_LIST_NULL jne dequeue_intermediate_SCB;
dequeue_first_scb:
        shr     SINDEX, 4, SAVED_SCSIID;
        INDEX_DISC_LIST_SCB(SINDEX, SAVED_LUN);
        /* Update list head. */
        bmov    DINDIR, REG2, 2;
        jmp     dequeue_restore;
dequeue_intermediate_SCB:
        bmov    SCBPTR, REG0, 2;
        bmov    SCB_NEXT, REG2, 2;
dequeue_restore:
        bmov    SCBPTR, REG1, 2;

/*
 * Ensure that the SCB the tag points to is for
 * an SCB transaction to the reconnecting target.
 */
setup_SCB:
        if ((ahd->flags & AHD_SEQUENCER_DEBUG) != 0) {
                or      SEQ_FLAGS, 0x10;
        }
        test    SCB_CONTROL,DISCONNECTED jz not_found;
        and     SCB_CONTROL,~DISCONNECTED;
        clr     SEQ_FLAGS;      /* make note of IDENTIFY */
        test    SCB_SGPTR, SG_LIST_NULL jnz . + 2;
        call    allocate_fifo;
/*      mvi     SEQINTCODE, PRINT_RESIDUALS; */
        /* See if the host wants to send a message upon reconnection */
        test    SCB_CONTROL, MK_MESSAGE jz mesgin_done;
        mvi     HOST_MSG        call mk_mesg;
        jmp     mesgin_done;

not_found:
        mvi     SEQINTCODE, NO_MATCH;
        jmp     mesgin_done;

not_found_ITloop:
        mvi     SEQINTCODE, NO_MATCH;
        jmp     ITloop;

/*
 * We received a "command complete" message.  Put the SCB on the complete
 * queue and trigger a completion interrupt via the idle loop.  Before doing
 * so, check to see if there
 * is a residual or the status byte is something other than STATUS_GOOD (0).
 * In either of these conditions, we upload the SCB back to the host so it can
 * process this information.  In the case of a non zero status byte, we 
 * additionally interrupt the kernel driver synchronously, allowing it to
 * decide if sense should be retrieved.  If the kernel driver wishes to request
 * sense, it will fill the kernel SCB with a request sense command, requeue
 * it to the QINFIFO and tell us not to post to the QOUTFIFO by setting 
 * RETURN_1 to SEND_SENSE.
 */
mesgin_complete:

        /*
         * If ATN is raised, we still want to give the target a message.
         * Perhaps there was a parity error on this last message byte.
         * Either way, the target should take us to message out phase
         * and then attempt to complete the command again.  We should use a
         * critical section here to guard against a timeout triggering
         * for this command and setting ATN while we are still processing
         * the completion.
        test    SCSISIGI, ATNI jnz mesgin_done;
         */

        /*
         * If the target never sent an identify message but instead went
         * to mesgin to give an invalid message, let the host abort us.
         */
        test    SEQ_FLAGS, NOT_IDENTIFIED|NO_CDB_SENT   jz . + 3;
        mvi     SEQINTCODE, PROTO_VIOLATION;
        jmp     mesgin_done;

        /*
         * If the target never gave us status information, have
         * the host abort the command.
         */
        test    SCB_CONTROL, STATUS_RCVD jz . - 2;

        /*
         * See if we attempted to deliver a message but the target ingnored us.
         */
        test    SCB_CONTROL, MK_MESSAGE jz . + 2;
        mvi     SEQINTCODE, MKMSG_FAILED;
        call    queue_scb_completion;
        jmp     await_busfree;

freeze_queue:
        /* Cancel any pending select-out. */
        test    SSTAT0, SELDO jnz . + 2;
        and     SCSISEQ0, ~ENSELO;
        mov     ACCUM_SAVE, A;
        clr     A;
        add     QFREEZE_COUNT, 1;
        adc     QFREEZE_COUNT[1], A;
        or      SEQ_FLAGS2, SELECTOUT_QFROZEN;
        mov     A, ACCUM_SAVE ret;

queue_arg1_scb_completion:
        SET_MODE(M_SCSI, M_SCSI);
        bmov    SCBPTR, ARG_1, 2;
queue_scb_completion:
        test    SCB_SCSI_STATUS,0xff    jnz bad_status;
        /*
         * Check for residuals
         */
        test    SCB_SGPTR, SG_LIST_NULL jnz complete;   /* No xfer */
        test    SCB_SGPTR, SG_FULL_RESID jnz upload_scb;/* Never xfered */
        test    SCB_RESIDUAL_SGPTR, SG_LIST_NULL jz upload_scb;
complete:
        bmov    SCB_NEXT_COMPLETE, COMPLETE_SCB_HEAD, 2;
        bmov    COMPLETE_SCB_HEAD, SCBPTR, 2 ret;
bad_status:
        cmp     SCB_SCSI_STATUS, STATUS_PKT_SENSE je upload_scb;
        call    freeze_queue;
upload_scb:
        bmov    SCB_NEXT_COMPLETE, COMPLETE_DMA_SCB_HEAD, 2;
        bmov    COMPLETE_DMA_SCB_HEAD, SCBPTR, 2;
        or      SCB_SGPTR, SG_STATUS_VALID ret;

/*
 * Is it a disconnect message?  Set a flag in the SCB to remind us
 * and await the bus going free.  If this is an untagged transaction
 * store the SCB id for it in our untagged target table for lookup on
 * a reselction.
 */
mesgin_disconnect:
        /*
         * If ATN is raised, we still want to give the target a message.
         * Perhaps there was a parity error on this last message byte
         * or we want to abort this command.  Either way, the target
         * should take us to message out phase and then attempt to
         * disconnect again.
         * XXX - Wait for more testing.
        test    SCSISIGI, ATNI jnz mesgin_done;
         */
        test    SEQ_FLAGS, NOT_IDENTIFIED|NO_CDB_SENT   jz disconnect_allowed;
        mvi     SEQINTCODE, PROTO_VIOLATION;
        jmp     mesgin_done;
disconnect_allowed:
        or      SCB_CONTROL,DISCONNECTED;
        test    SCB_CONTROL, TAG_ENB jz queue_disc_scb;
        mov     A, SCB_NONPACKET_TAG;
        cmp     SCBPTR, A je await_busfree;
queue_disc_scb:
        bmov    REG0, SCBPTR, 2;
        shr     SINDEX, 4, SCB_SCSIID;
        INDEX_DISC_LIST(SINDEX, SCB_LUN);
        bmov    DINDEX, SINDEX, 2;
        bmov    REG1, SINDIR, 2;
        bmov    DINDIR, REG0, 2;
        bmov    SCBPTR, REG0, 2;
        bmov    SCB_NEXT, REG1, 2;
        /* FALLTHROUGH */
await_busfree:
        and     SIMODE1, ~ENBUSFREE;
        mov     NONE, SCSIDAT;          /* Ack the last byte */
        call    clear_target_state;
        test    MODE_PTR, ~(MK_MODE(M_DFF1, M_DFF1))
                jnz await_busfree_not_m_dff;
SET_SRC_MODE    M_DFF1;
SET_DST_MODE    M_DFF1;
await_busfree_clrchn:
        mvi     DFFSXFRCTL, CLRCHN;
await_busfree_not_m_dff:
        test    SSTAT1,REQINIT|BUSFREE  jz .;
        test    SSTAT1, BUSFREE jnz idle_loop;
        mvi     SEQINTCODE, MISSED_BUSFREE;


/*
 * Save data pointers message:
 * Copying RAM values back to SCB, for Save Data Pointers message, but
 * only if we've actually been into a data phase to change them.  This
 * protects against bogus data in scratch ram and the residual counts
 * since they are only initialized when we go into data_in or data_out.
 * Ack the message as soon as possible.  For chips without S/G pipelining,
 * we can only ack the message after SHADDR has been saved.  On these
 * chips, SHADDR increments with every bus transaction, even PIO.
 */
SET_SRC_MODE    M_DFF1;
SET_DST_MODE    M_DFF1;
mesgin_sdptrs:
        mov     NONE,SCSIDAT;           /*dummy read from latch to ACK*/
        test    SEQ_FLAGS, DPHASE       jz ITloop;
        call    save_pointers;
        jmp     ITloop;

save_pointers:
        /*
         * If we are asked to save our position at the end of the
         * transfer, just mark us at the end rather than perform a
         * full save.
         */
        test    SCB_RESIDUAL_SGPTR[0], SG_LIST_NULL jz save_pointers_full;
        or      SCB_SGPTR, SG_LIST_NULL ret;

save_pointers_full:
        /*
         * The SCB_DATAPTR becomes the current SHADDR.
         * All other information comes directly from our residual
         * state.
         */
        bmov    SCB_DATAPTR, SHADDR, 8;
        bmov    SCB_DATACNT, SCB_RESIDUAL_DATACNT, 8 ret;

/*
 * Restore pointers message?  Data pointers are recopied from the
 * SCB anytime we enter a data phase for the first time, so all
 * we need to do is clear the DPHASE flag and let the data phase
 * code do the rest.  We also reset/reallocate the FIFO to make
 * sure we have a clean start for the next data phase.
 */
mesgin_rdptrs:
        and     SEQ_FLAGS, ~DPHASE;
        test    MODE_PTR, ~(MK_MODE(M_DFF1, M_DFF1)) jnz msgin_rdptrs_get_fifo;
        mvi     DFFSXFRCTL, RSTCHN|CLRSHCNT;
msgin_rdptrs_get_fifo:
        call    allocate_fifo;
        jmp     mesgin_done;

clear_target_state:
        mvi     LASTPHASE, P_BUSFREE;
        /* clear target specific flags */
        mvi     SEQ_FLAGS, NOT_IDENTIFIED|NO_CDB_SENT ret;

phase_lock:     
        test    SCSIPHASE, 0xFF jz .;
phase_lock_latch_phase:
        and     LASTPHASE, PHASE_MASK, SCSISIGI ret;

/*
 * Functions to read data in Automatic PIO mode.
 *
 * An ACK is not sent on input from the target until SCSIDATL is read from.
 * So we wait until SCSIDATL is latched (the usual way), then read the data
 * byte directly off the bus using SCSIBUSL.  When we have pulled the ATN
 * line, or we just want to acknowledge the byte, then we do a dummy read
 * from SCISDATL.  The SCSI spec guarantees that the target will hold the
 * data byte on the bus until we send our ACK.
 *
 * The assumption here is that these are called in a particular sequence,
 * and that REQ is already set when inb_first is called.  inb_{first,next}
 * use the same calling convention as inb.
 */
inb_next:
        mov     NONE,SCSIDAT;           /*dummy read from latch to ACK*/
inb_next_wait:
        /*
         * If there is a parity error, wait for the kernel to
         * see the interrupt and prepare our message response
         * before continuing.
         */
        test    SCSIPHASE, 0xFF jz .;
inb_next_check_phase:
        and     LASTPHASE, PHASE_MASK, SCSISIGI;
        cmp     LASTPHASE, P_MESGIN jne mesgin_phasemis;
inb_first:
        clr     DINDEX[1];
        mov     DINDEX,SINDEX;
        mov     DINDIR,SCSIBUS  ret;            /*read byte directly from bus*/
inb_last:
        mov     NONE,SCSIDAT ret;               /*dummy read from latch to ACK*/

mk_mesg:
        mvi     SCSISIGO, ATNO;
        mov     MSG_OUT,SINDEX ret;

SET_SRC_MODE    M_DFF1;
SET_DST_MODE    M_DFF1;
disable_ccsgen:
        test    SG_STATE, FETCH_INPROG jz return;
        clr     SG_STATE;
disable_ccsgen_fetch_done:
        clr     CCSGCTL ret;

toggle_dff_mode:
        mvi     SEQINTCTL, INTVEC1DSL;
        xor     MODE_PTR, MK_MODE(M_DFF1, M_DFF1);
        clr     SEQINTCTL ret;

data_group_idle_loop:
        mov     SAVED_MODE, MODE_PTR;
        test    SG_STATE, LOADING_NEEDED jz . + 2;
        call    service_fifo;
        call    toggle_dff_mode;
        test    SG_STATE, LOADING_NEEDED jz . + 2;
        call    service_fifo;
        call    idle_loop_cchan;
        mov     SAVED_MODE jmp set_mode_work_around;

service_fifo:
        /*
         * Do we have any prefetch left???
         */
        test    SG_STATE, SEGS_AVAIL jnz idle_sg_avail;

        /*
         * Can this FIFO have access to the S/G cache yet?
         */
        test    CCSGCTL, SG_CACHE_AVAIL jz return;

        /* Did we just finish fetching segs? */
        cmp     CCSGCTL, CCSGEN|SG_CACHE_AVAIL|CCSGDONE
                je idle_sgfetch_complete;

        /* Are we actively fetching segments? */
        test    CCSGCTL, CCSGEN jnz return;

        /*
         * We fetch a "cacheline aligned" and sized amount of data
         * so we don't end up referencing a non-existant page.
         * Cacheline aligned is in quotes because the kernel will
         * set the prefetch amount to a reasonable level if the
         * cacheline size is unknown.
         */
        mvi     SGHCNT, SG_PREFETCH_CNT;
        and     SGHADDR[0], SG_PREFETCH_ALIGN_MASK, SCB_RESIDUAL_SGPTR;
        bmov    SGHADDR[1], SCB_RESIDUAL_SGPTR[1], 3;
        mvi     CCSGCTL, CCSGEN|SG_CACHE_AVAIL|CCSGRESET;
        or      SG_STATE, FETCH_INPROG ret;
idle_sgfetch_complete:
        /*
         * Guard against SG_CACHE_AVAIL activating during sg fetch
         * request in the other FIFO.
         */
        test    SG_STATE, FETCH_INPROG jz return;
        call    disable_ccsgen_fetch_done;
        and     CCSGADDR, SG_PREFETCH_ADDR_MASK, SCB_RESIDUAL_SGPTR;
        mvi     SG_STATE, SEGS_AVAIL|LOADING_NEEDED;
idle_sg_avail:
        /* Does the hardware have space for another SG entry? */
        test    DFSTATUS, PRELOAD_AVAIL jz return;
        if ((ahd->flags & AHD_64BIT_ADDRESSING) != 0) {
                bmov    HADDR, CCSGRAM, 8;
        } else {
                bmov    HADDR, CCSGRAM, 4;
        }
        bmov    HCNT, CCSGRAM, 3;
        test    HCNT[0], 0x1 jz . + 2;
        xor     DATA_COUNT_ODD, 0x1;
        bmov    SCB_RESIDUAL_DATACNT[3], CCSGRAM, 1;
        if ((ahd->flags & AHD_39BIT_ADDRESSING) != 0) {
                and     HADDR[4], SG_HIGH_ADDR_BITS, SCB_RESIDUAL_DATACNT[3];
        }
        if ((ahd->flags & AHD_64BIT_ADDRESSING) != 0) {
                /* Skip 4 bytes of pad. */
                add     CCSGADDR, 4;
        }
sg_advance:
        clr     A;                      /* add sizeof(struct scatter) */
        add     SCB_RESIDUAL_SGPTR[0],SG_SIZEOF;
        adc     SCB_RESIDUAL_SGPTR[1],A;
        adc     SCB_RESIDUAL_SGPTR[2],A;
        adc     SCB_RESIDUAL_SGPTR[3],A;
        mov     SINDEX, SCB_RESIDUAL_SGPTR[0];
        test    DATA_COUNT_ODD, 0x1 jz . + 2;
        or      SINDEX, ODD_SEG;
        test    SCB_RESIDUAL_DATACNT[3], SG_LAST_SEG jz . + 3;
        or      SINDEX, LAST_SEG;
        clr     SG_STATE;
        mov     SG_CACHE_PRE, SINDEX;
        /*
         * Load the segment.  Or in HDMAEN here too
         * just in case HDMAENACK has not come true
         * by the time this segment is loaded.  If
         * HDMAENACK is not true, this or will disable
         * HDMAEN mid-transfer.  We do not want to simply
         * mvi our original settings as SCSIEN automatically
         * de-asserts and we don't want to accidentally
         * re-enable it.
         */
        or      DFCNTRL, PRELOADEN|HDMAEN;
        /*
         * Do we have another segment in the cache?
         */
        add     NONE, SG_PREFETCH_CNT_LIMIT, CCSGADDR;
        jnc     return;
        and     SG_STATE, ~SEGS_AVAIL ret;

/*
 * Initialize the DMA address and counter from the SCB.
 */
load_first_seg:
        bmov    HADDR, SCB_DATAPTR, 11;
        and     DATA_COUNT_ODD, 0x1, SCB_DATACNT[0];
        and     REG0, ~SG_FULL_RESID, SCB_SGPTR[0];
        test    SCB_DATACNT[3], SG_LAST_SEG jz . + 2;
        or      REG0, LAST_SEG;
        test    DATA_COUNT_ODD, 0x1 jz . + 2;
        or      REG0, ODD_SEG;
        mov     SG_CACHE_PRE, REG0;
        mvi     DFCNTRL, (PRELOADEN|SCSIEN|HDMAEN);
        /*
         * Since we've are entering a data phase, we will
         * rely on the SCB_RESID* fields.  Initialize the
         * residual and clear the full residual flag.
         */
        and     SCB_SGPTR[0], ~SG_FULL_RESID;
        bmov    SCB_RESIDUAL_DATACNT[3], SCB_DATACNT[3], 5;
        /* If we need more S/G elements, tell the idle loop */
        test    SCB_RESIDUAL_DATACNT[3], SG_LAST_SEG jnz . + 2;
        mvi     SG_STATE, LOADING_NEEDED ret;
        clr     SG_STATE ret;

p_data:
        test    SEQ_FLAGS, NOT_IDENTIFIED|NO_CDB_SENT   jz p_data_allowed;
        mvi     SEQINTCODE, PROTO_VIOLATION;
p_data_allowed:
 
        test    SEQ_FLAGS, DPHASE       jz data_phase_initialize;

        /*
         * If we re-enter the data phase after going through another
         * phase, our transfer location has almost certainly been
         * corrupted by the interveining, non-data, transfers.  Ask
         * the host driver to fix us up based on the transfer residual
         * unless we already know that we should be bitbucketing.
         */
        test    SCB_RESIDUAL_SGPTR[0], SG_LIST_NULL jnz p_data_bitbucket;
        mvi     SEQINTCODE, PDATA_REINIT;

p_data_bitbucket:
        /*
         * Turn on `Bit Bucket' mode, wait until the target takes
         * us to another phase, and then notify the host.
         */
        test    MODE_PTR, ~(MK_MODE(M_DFF1, M_DFF1))
                jnz bitbucket_not_m_dff;
        /*
         * Ensure that any FIFO contents are cleared out and the
         * FIFO free'd prior to starting the BITBUCKET.  BITBUCKET
         * doesn't discard data already in the FIFO.
         */
        mvi     DFFSXFRCTL, RSTCHN|CLRSHCNT;
        SET_MODE(M_SCSI, M_SCSI);
bitbucket_not_m_dff:
        or      SXFRCTL1,BITBUCKET;
        test    SCSIPHASE, DATA_PHASE_MASK jnz .;
        and     SXFRCTL1, ~BITBUCKET;
        SET_MODE(M_DFF1, M_DFF1);
        mvi     SEQINTCODE, DATA_OVERRUN;
        jmp     ITloop;

data_phase_initialize:
        test    SCB_SGPTR[0], SG_LIST_NULL jnz p_data_bitbucket;
        call    load_first_seg;
data_phase_inbounds:
        /* We have seen a data phase at least once. */
        or      SEQ_FLAGS, DPHASE;
data_group_dma_loop:
        /*
         * The transfer is complete if either the last segment
         * completes or the target changes phase.  Both conditions
         * will clear SCSIEN.  We test SCSIEN twice during our
         * "idle loop" to avoid long delays before we notice the
         * SCSIEN transition.
         */
        call    data_group_idle_loop;
        test    DFCNTRL, SCSIEN jnz data_group_dma_loop;

data_group_dmafinish:
        /*
         * The transfer has terminated either due to a phase
         * change, and/or the completion of the last segment.
         * We have two goals here.  Do as much other work
         * as possible while the data fifo drains on a read
         * and respond as quickly as possible to the standard
         * messages (save data pointers/disconnect and command
         * complete) that usually follow a data phase.
         */
        call    calc_residual;

        /*
         * Go ahead and shut down the DMA engine now.
         */
        test    DFCNTRL, DIRECTION jnz data_phase_finish;
data_group_fifoflush:
        if ((ahd->bugs & AHD_AUTOFLUSH_BUG) != 0) {
                or      DFCNTRL, FIFOFLUSH;
        }
        /*
         * We have enabled the auto-ack feature.  This means
         * that the controller may have already transferred
         * some overrun bytes into the data FIFO and acked them
         * on the bus.  The only way to detect this situation is
         * to wait for LAST_SEG_DONE to come true on a completed
         * transfer and then test to see if the data FIFO is
         * non-empty.  We know there is more data yet to transfer
         * if SG_LIST_NULL is not yet set, thus there cannot be
         * an overrun.
         */
        test    SCB_RESIDUAL_SGPTR[0], SG_LIST_NULL jz data_phase_finish;
        test    SG_CACHE_SHADOW, LAST_SEG_DONE jz .;
        test    DFSTATUS, FIFOEMP jnz data_phase_finish;
        /* Overrun */
        jmp     p_data;
data_phase_finish:
        /*
         * If the target has left us in data phase, loop through
         * the dma code again.  We will only loop if there is a
         * data overrun.  
         */
        if ((ahd->flags & AHD_TARGETROLE) != 0) {
                test    SSTAT0, TARGET jnz data_phase_done;
        }
        if ((ahd->flags & AHD_INITIATORROLE) != 0) {
                test    SSTAT1, REQINIT jz .;
                test    SCSIPHASE, DATA_PHASE_MASK jnz p_data;
        }

data_phase_done:
        /* Kill off any pending prefetch */
        call    disable_ccsgen;

        if ((ahd->flags & AHD_TARGETROLE) != 0) {
                test    SEQ_FLAGS, DPHASE_PENDING jz ITloop;
                /*
                and     SEQ_FLAGS, ~DPHASE_PENDING;
                 * For data-in phases, wait for any pending acks from the
                 * initiator before changing phase.  We only need to
                 * send Ignore Wide Residue messages for data-in phases.
                test    DFCNTRL, DIRECTION jz target_ITloop;
                test    SSTAT1, REQINIT jnz .;
                test    DATA_COUNT_ODD, 0x1 jz target_ITloop;
                SET_MODE(M_SCSI, M_SCSI);
                test    NEGCONOPTS, WIDEXFER jz target_ITloop;
                 */
                /*
                 * Issue an Ignore Wide Residue Message.
                mvi     P_MESGIN|BSYO call change_phase;
                mvi     MSG_IGN_WIDE_RESIDUE call target_outb;
                mvi     1 call target_outb;
                jmp     target_ITloop;
                 */
        } else {
                jmp     ITloop;
        }

/*
 * We assume that, even though data may still be
 * transferring to the host, that the SCSI side of
 * the DMA engine is now in a static state.  This
 * allows us to update our notion of where we are
 * in this transfer.
 *
 * If, by chance, we stopped before being able
 * to fetch additional segments for this transfer,
 * yet the last S/G was completely exhausted,
 * call our idle loop until it is able to load
 * another segment.  This will allow us to immediately
 * pickup on the next segment on the next data phase.
 *
 * If we happened to stop on the last segment, then
 * our residual information is still correct from
 * the idle loop and there is no need to perform
 * any fixups.
 */
calc_residual:
        test    SG_CACHE_SHADOW, LAST_SEG jz residual_before_last_seg;
        /* Record if we've consumed all S/G entries */
        test    MDFFSTAT, SHVALID       jz . + 2;
        bmov    SCB_RESIDUAL_DATACNT, SHCNT, 3 ret;
        or      SCB_RESIDUAL_SGPTR[0], SG_LIST_NULL ret;
residual_before_last_seg:
        test    MDFFSTAT, SHVALID       jnz sgptr_fixup;
        /*
         * Can never happen from an interrupt as the packetized
         * hardware will only interrupt us once SHVALID or
         * LAST_SEG_DONE.
         */
        call    data_group_idle_loop;
        jmp     calc_residual;

sgptr_fixup:
        /*
         * Fixup the residual next S/G pointer.  The S/G preload
         * feature of the chip allows us to load two elements
         * in addition to the currently active element.  We
         * store the bottom byte of the next S/G pointer in
         * the SG_CACHE_PTR register so we can restore the
         * correct value when the DMA completes.  If the next
         * sg ptr value has advanced to the point where higher
         * bytes in the address have been affected, fix them
         * too.
         */
        test    SG_CACHE_SHADOW, 0x80 jz sgptr_fixup_done;
        test    SCB_RESIDUAL_SGPTR[0], 0x80 jnz sgptr_fixup_done;
        add     SCB_RESIDUAL_SGPTR[1], -1;
        adc     SCB_RESIDUAL_SGPTR[2], -1; 
        adc     SCB_RESIDUAL_SGPTR[3], -1;
sgptr_fixup_done:
        and     SCB_RESIDUAL_SGPTR[0], SG_ADDR_MASK, SG_CACHE_SHADOW;
        clr     DATA_COUNT_ODD;
        test    SG_CACHE_SHADOW, ODD_SEG jz . + 2;
        or      DATA_COUNT_ODD, 0x1;
        clr     SCB_RESIDUAL_DATACNT[3]; /* We are not the last seg */
        bmov    SCB_RESIDUAL_DATACNT, SHCNT, 3 ret;

export seq_isr:
        nop;    /* Jumps in the first ISR instruction fail on Rev A. */
        test    SEQINTSRC, SAVEPTRS     jnz saveptr_intr;
        test    SEQINTSRC, CFG4DATA     jnz cfg4data_intr;
        test    SEQINTSRC, CFG4ISTAT    jnz cfg4istat_intr;
        test    SEQINTSRC, CFG4ICMD     jnz cfg4icmd_intr;
        mvi     SEQINTCODE, INVALID_SEQINT;

/*
 * There are two types of save pointers interrupts:
 * The first is a snapshot save pointers where the current FIFO is not
 * active and contains a snapshot of the current poniter information.
 * This happens between packets in a stream for a single L_Q.  Since we
 * are not performing a pointer save, we can safely clear the channel
 * so it can be used for other transactions.
 *
 * The second case is a save pointers on an active FIFO which occurs
 * if the target changes to a new L_Q or busfrees/QAS' and the transfer
 * has a residual.  This should occur coincident with a ctxtdone.  We
 * disable the interrupt and allow our active routine to handle the
 * save.
 */
saveptr_intr:
        test    DFCNTRL, HDMAENACK jz snapshot_saveptr;
        and     SEQIMODE, ~ENSAVEPTRS;
        or      SEQINTCTL, IRET ret;
snapshot_saveptr:
        mvi     DFFSXFRCTL, CLRCHN;
        or      SEQINTCTL, IRET ret;

cfg4data_intr:
        test    SCB_SGPTR[0], SG_LIST_NULL jnz pkt_handle_overrun;
        call    load_first_seg;
        call    pkt_handle_xfer;
        or      SEQINTCTL, IRET ret;

cfg4istat_intr:
        call    freeze_queue;
        add     NONE, -13, SCB_CDB_LEN;
        jnc     cfg4istat_have_sense_addr;
        test    SCB_CDB_LEN, SCB_CDB_LEN_PTR jnz cfg4istat_have_sense_addr;
        /*
         * Host sets up address/count and enables transfer.
         */
        mvi     SEQINTCODE, CFG4ISTAT_INTR;
        jmp     cfg4istat_setup_handler;
cfg4istat_have_sense_addr:
        bmov    HADDR, SCB_SENSE_BUSADDR, 4;
        mvi     HCNT[1], (AHD_SENSE_BUFSIZE >> 8);
        mvi     SG_CACHE_PRE, LAST_SEG;
        mvi     DFCNTRL, PRELOADEN|SCSIEN|HDMAEN;
cfg4istat_setup_handler:
        /*
         * Status pkt is transferring to host.
         * Wait in idle loop for transfer to complete.
         */
        call    pkt_handle_status;
        or      SEQINTCTL, IRET ret;

/*
 * See if the target has gone on in this context creating an
 * overrun condition.  For the write case, the hardware cannot
 * ack bytes until data is provided.  So, if the target begins
 * another  packet without changing contexts, implying we are
 * not sitting on a packet boundary, we are in an overrun
 * situation.  For the read case, the hardware will continue to
 * ack bytes into the FIFO, and may even ack the last overrun packet
 * into the FIFO.   If the FIFO should become non-empty, we are in
 * a read overrun case.
 */
#define check_overrun                                                   \
        /* Not on a packet boundary. */                                 \
        test    MDFFSTAT, DLZERO jz pkt_handle_overrun;                 \
        test    DFSTATUS, FIFOEMP jz pkt_handle_overrun

pkt_handle_xfer:
        bmov    LONGJMP_SCB, SCBPTR, 2;
        test    SG_STATE, LOADING_NEEDED jz pkt_last_seg;
        call    setjmp;
        test    SEQINTSRC, SAVEPTRS jnz pkt_saveptrs;
        test    SCSIPHASE, ~DATA_PHASE_MASK jz . + 2;
        test    SCSISIGO, ATNO jnz . + 2;
        test    SSTAT2, NONPACKREQ jz pkt_service_fifo;
        /*
         * Defer handling of this NONPACKREQ until we
         * can be sure it pertains to this FIFO.  SAVEPTRS
         * will not be asserted if the NONPACKREQ is for us,
         * so we must simulate it if shaddow is valid.  If
         * shaddow is not valid, keep running this FIFO until we
         * have satisfied the transfer by loading segments and
         * waiting for either shaddow valid or last_seg_done.
         */
        test    MDFFSTAT, SHVALID jnz pkt_saveptrs;
pkt_service_fifo:
        test    SG_STATE, LOADING_NEEDED jnz service_fifo;
pkt_last_seg:
        call    setjmp;
        test    SEQINTSRC, SAVEPTRS jnz pkt_saveptrs;
        test    SG_CACHE_SHADOW, LAST_SEG_DONE jnz last_pkt_done;
        test    SCSIPHASE, ~DATA_PHASE_MASK jz . + 2;
        test    SCSISIGO, ATNO jnz . + 2;
        test    SSTAT2, NONPACKREQ jz return;
        test    MDFFSTAT, SHVALID jnz pkt_saveptrs;
        jmp     return;
last_pkt_done:
BEGIN_CRITICAL;
        if ((ahd->bugs & AHD_AUTOFLUSH_BUG) != 0) {
                or      DFCNTRL, FIFOFLUSH;
        }
        test    SCB_CONTROL, STATUS_RCVD jz wait_pkt_end;
        check_overrun;
        or      SCB_SGPTR, SG_LIST_NULL;
        /*
         * I think it is safe to skip the FIFO check.
         * in this case as LAST_SEG_DONE implies
         * the other FIFO, if ever active for this transfer,
         * has completed.
         */
last_pkt_queue_scb:
        or      LONGJMP_ADDR[1], INVALID_ADDR;
        bmov    ARG_1, SCBPTR, 2;
        mvi     DFFSXFRCTL, CLRCHN;
        jmp     queue_arg1_scb_completion;

last_pkt_complete:
        bmov    ARG_1, SCBPTR, 2;
        mvi     DFFSXFRCTL, CLRCHN;
check_other_fifo:
        clc;
        call    toggle_dff_mode;
        call    check_fifo;
        jnc     queue_arg1_scb_completion;
return:
        ret;

wait_pkt_end:
        call    setjmp;
END_CRITICAL;
wait_pkt_end_loop:
        test    SEQINTSRC, CTXTDONE jnz pkt_end;
        check_overrun;
        test    SSTAT2, NONPACKREQ jz return;
        test    SEQINTSRC, CTXTDONE jz unexpected_nonpkt_phase;
pkt_end:
BEGIN_CRITICAL;
        check_overrun;
        or      LONGJMP_ADDR[1], INVALID_ADDR;
        or      SCB_SGPTR, SG_LIST_NULL;
        test    SCB_CONTROL, STATUS_RCVD jnz last_pkt_complete;
        mvi     DFFSXFRCTL, CLRCHN ret;
END_CRITICAL;

/*
 * Either a SAVEPTRS interrupt condition is pending for this FIFO
 * or we have a pending nonpackreq for this FIFO.  We differentiate
 * between the two by capturing the state of the SAVEPTRS interrupt
 * prior to clearing and handling the common code of these two cases.
 */
pkt_saveptrs:
BEGIN_CRITICAL;
        if ((ahd->bugs & AHD_AUTOFLUSH_BUG) != 0) {
                or      DFCNTRL, FIFOFLUSH;
        }
        mov     REG0, SEQINTSRC;
        mvi     CLRSEQINTSRC, CLRSAVEPTRS;
        call    calc_residual;
        call    save_pointers;
        call    disable_ccsgen;
        or      SEQIMODE, ENSAVEPTRS;
        or      LONGJMP_ADDR[1], INVALID_ADDR;
pkt_saveptrs_check_status:
        test    REG0, SAVEPTRS jz unexpected_nonpkt_phase;
        test    SCB_CONTROL, STATUS_RCVD jz pkt_saveptrs_clrchn;
        jmp     last_pkt_complete;
pkt_saveptrs_clrchn:
        mvi     DFFSXFRCTL, CLRCHN ret;
END_CRITICAL;

check_status_overrun:
        test    SHCNT[2], 0xFF jz status_IU_done;
        mvi     SEQINTCODE, STATUS_OVERRUN;
        jmp     status_IU_done;
pkt_handle_status:
        call    setjmp_setscb;
        test    MDFFSTAT, LASTSDONE jnz check_status_overrun;
        test    SEQINTSRC, CTXTDONE jz return;
status_IU_done:
BEGIN_CRITICAL;
        if ((ahd->bugs & AHD_AUTOFLUSH_BUG) != 0) {
                or      DFCNTRL, FIFOFLUSH;
        }
        or      LONGJMP_ADDR[1], INVALID_ADDR;
        mvi     SCB_SCSI_STATUS, STATUS_PKT_SENSE;
        or      SCB_CONTROL, STATUS_RCVD;
        jmp     last_pkt_complete;
END_CRITICAL;

SET_SRC_MODE    M_DFF0;
SET_DST_MODE    M_DFF0;
BEGIN_CRITICAL;
check_fifo:
        test    LONGJMP_ADDR[1], INVALID_ADDR jnz return;
        mov     A, ARG_2;
        cmp     LONGJMP_SCB[1], A       jne return;
        mov     A, ARG_1;
        cmp     LONGJMP_SCB[0], A       jne return;
        stc     ret;
END_CRITICAL;

/*
 * Nonpackreq is a polled status.  It can come true in three situations:
 * we have received an L_Q, we have sent one or more L_Qs, or there is no
 * L_Q context associated with this REQ (REQ occurs immediately after a
 * (re)selection).  Routines that know that the context responsible for this
 * nonpackreq call directly into unexpected_nonpkt_phase.  In the case of the
 * top level idle loop, we exhaust all active contexts prior to determining that
 * we simply do not have the full I_T_L_Q for this phase.
 */
unexpected_nonpkt_phase_find_ctxt:
        /*
         * This nonpackreq is most likely associated with one of the tags
         * in a FIFO or an outgoing LQ.  Only treat it as an I_T only
         * nonpackreq if we've cleared out the FIFOs and handled any
         * pending SELDO.
         */
SET_SRC_MODE    M_SCSI;
SET_DST_MODE    M_SCSI;
        and     A, FIFO1FREE|FIFO0FREE, DFFSTAT;
        cmp     A, FIFO1FREE|FIFO0FREE jne return;
        test    SSTAT0, SELDO jnz return;
        mvi     SCBPTR[1], SCB_LIST_NULL;
unexpected_nonpkt_phase:
        test    MODE_PTR, ~(MK_MODE(M_DFF1, M_DFF1)) jnz . + 3;
SET_SRC_MODE    M_DFF0;
SET_DST_MODE    M_DFF0;
        or      LONGJMP_ADDR[1], INVALID_ADDR;
        mvi     DFFSXFRCTL, CLRCHN;
        mvi     CLRSINT2, CLRNONPACKREQ;
        test    SCSIPHASE, ~(MSG_IN_PHASE|MSG_OUT_PHASE) jnz illegal_phase;
        mvi     SEQINTCODE, ENTERING_NONPACK;
        jmp     ITloop;

illegal_phase:
        mvi     SEQINTCODE, ILLEGAL_PHASE;
        jmp     ITloop;

/*
 * We have entered an overrun situation.  If we have working
 * BITBUCKET, flip that on and let the hardware eat any overrun
 * data.  Otherwise use an overrun buffer in the host to simulate
 * BITBUCKET.
 */
pkt_handle_overrun:
        mvi     SEQINTCODE, CFG4OVERRUN;
        call    freeze_queue;
        if ((ahd->bugs & AHD_PKT_BITBUCKET_BUG) == 0) {
                SET_MODE(M_SCSI, M_SCSI);
                or      SXFRCTL1,BITBUCKET;
SET_SRC_MODE    M_DFF1;
SET_DST_MODE    M_DFF1;
        } else {
                call    load_overrun_buf;
                mvi     DFCNTRL, (HDMAEN|SCSIEN|PRELOADEN);
        }
        call    setjmp;
        if ((ahd->bugs & AHD_PKT_BITBUCKET_BUG) != 0) {
                test    DFSTATUS, PKT_PRELOAD_AVAIL jz overrun_load_done;
                call    load_overrun_buf;
                or      DFCNTRL, PRELOADEN;
overrun_load_done:
        }
        test    SEQINTSRC, CTXTDONE jnz pkt_overrun_end;
        test    SSTAT2, NONPACKREQ jz return;
pkt_overrun_end:
        or      SCB_RESIDUAL_SGPTR, SG_OVERRUN_RESID;
        test    SEQINTSRC, CTXTDONE jz unexpected_nonpkt_phase;
        test    SCB_CONTROL, STATUS_RCVD jnz last_pkt_queue_scb;
        mvi     DFFSXFRCTL, CLRCHN ret;

if ((ahd->bugs & AHD_PKT_BITBUCKET_BUG) != 0) {
load_overrun_buf:
        /*
         * Load a dummy segment if preload space is available.
         */
        mov     HADDR[0], SHARED_DATA_ADDR;
        add     HADDR[1], PKT_OVERRUN_BUFOFFSET, SHARED_DATA_ADDR[1];
        mov     ACCUM_SAVE, A;
        clr     A;
        adc     HADDR[2], A, SHARED_DATA_ADDR[2];
        adc     HADDR[3], A, SHARED_DATA_ADDR[3];
        mov     A, ACCUM_SAVE;
        bmov    HADDR[4], ALLZEROS, 4;
        /* PKT_OVERRUN_BUFSIZE is a multiple of 256 */
        clr     HCNT[0];
        mvi     HCNT[1], ((PKT_OVERRUN_BUFSIZE >> 8) & 0xFF);
        clr     HCNT[2];
}

cfg4icmd_intr: