2 * Copyright (c) 1998 Robert Nordier
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
18 /* Memory Locations */
19 .set MEM_REL,0x700 # Relocation address
20 .set MEM_ARG,0x900 # Arguments
21 .set MEM_ORG,0x7c00 # Origin
22 .set MEM_BUF,0x8000 # Load area
23 .set MEM_BTX,0x9000 # BTX start
24 .set MEM_JMP,0x9010 # BTX entry point
25 .set MEM_USR,0xa000 # Client start
26 .set BDA_BOOT,0x472 # Boot howto flag
28 /* Partition Constants */
29 .set PRT_OFF,0x1be # Partition offset
30 .set PRT_NUM,0x4 # Partitions
31 .set PRT_BSD,0xa5 # Partition type
34 .set FL_PACKET,0x80 # Packet mode
37 .set SIZ_PAG,0x1000 # Page size
38 .set SIZ_SEC,0x200 # Sector size
45 start: jmp main # Start recognizably
48 * This is the start of a standard BIOS Parameter Block (BPB). Most bootable
49 * FAT disks have this at the start of their MBR. While normal BIOS's will
50 * work fine without this section, IBM's El Torito emulation "fixes" up the
51 * BPB by writing into the memory copy of the MBR. Rather than have data
52 * written into our xread routine, we'll define a BPB to work around it.
53 * The data marked with (T) indicates a field required for a ThinkPad to
54 * recognize the disk and (W) indicates fields written from IBM BIOS code.
55 * The use of the BPB is based on what OpenBSD and NetBSD implemented in
56 * their boot code but the required fields were determined by trial and error.
58 * Note: If additional space is needed in boot1, one solution would be to
59 * move the "prompt" message data (below) to replace the OEM ID.
62 oemid: .space 0x08, 0x00 # OEM ID
65 bpb: .word 512 # sector size (T)
66 .byte 0 # sectors/clustor
67 .word 0 # reserved sectors
68 .byte 0 # number of FATs
69 .word 0 # root entries
70 .word 0 # small sectors
71 .byte 0 # media type (W)
73 .word 18 # sectors per track (T)
74 .word 2 # number of heads (T)
75 .long 0 # hidden sectors (W)
76 .long 0 # large sectors
79 ebpb: .byte 0 # BIOS physical drive number (W)
83 * Trampoline used by boot2 to call read to read data from the disk via
84 * the BIOS. Call with:
86 * %ecx:%eax - long - LBA to read in
87 * %es:(%bx) - caddr_t - buffer to read data into
88 * %dl - byte - drive to read from
89 * %dh - byte - num sectors to read
92 xread: push %ss # Address
95 * Setup an EDD disk packet and pass it to read
97 xread.1: pushl %ecx # Starting absolute block
98 pushl %eax # block number
100 push %bx # transfer buffer
101 xor %ax,%ax # Number of
102 movb %dh,%al # blocks to
104 push $0x10 # Size of packet
105 mov %sp,%bp # Packet pointer
106 callw read # Read from disk
107 lea 0x10(%bp),%sp # Clear stack
110 * Load the rest of boot2 and BTX up, copy the parts to the right locations,
111 * and start it all up.
115 * Setup the segment registers to flat addressing (segment 0) and setup the
116 * stack to end just below the start of our code.
118 main: cld # String ops inc
120 mov %cx,%es # Address
123 mov $start,%sp # stack
125 * Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
129 mov $MEM_REL,%di # Destination
130 incb %ch # Word count
134 * If we are on a hard drive, then load the MBR and look for the first
135 * FreeBSD slice. We use the fake partition entry below that points to
136 * the MBR when we call nread. The first pass looks for the first active
137 * FreeBSD slice. The second pass looks for the first non-active FreeBSD
138 * slice if the first one fails.
140 mov $part4,%si # Partition
141 cmpb $0x80,%dl # Hard drive?
143 movb $0x1,%dh # Block count
144 callw nread # Read MBR
145 mov $0x1,%cx # Two passes
146 main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table
147 movb $0x1,%dh # Partition
148 main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type?
150 jcxz main.5 # If second pass
151 testb $0x80,(%si) # Active?
153 main.3: add $0x10,%si # Next entry
155 cmpb $0x1+PRT_NUM,%dh # In table?
160 * If we get here, we didn't find any FreeBSD slices at all, so print an
161 * error message and die.
163 mov $msg_part,%si # Message
166 * Floppies use partition 0 of drive 0.
168 main.4: xor %dx,%dx # Partition:drive
171 * Ok, we have a slice and drive in %dx now, so use that to locate and
172 * load boot2. %si references the start of the slice we are looking
173 * for, so go ahead and load up the 64 sectors starting at sector 1024
174 * (i.e. after the two vdev labels). We don't have do anything fancy
175 * here to allow for an extra copy of boot1 and a partition table
176 * (compare to this section of the UFS bootstrap) so we just load it
177 * all at 0x8000. The first part of boot2 is BTX, which wants to run
178 * at 0x9000. The boot2.bin binary starts right after the end of BTX,
179 * so we have to figure out where the start of it is and then move the
180 * binary to 0xc000. After we have moved the client, we relocate BTX
181 * itself to 0x9000 - doing it in this order means that none of the
182 * memcpy regions overlap which would corrupt the copy. Normally, BTX
183 * clients start at MEM_USR, or 0xa000, but when we use btxld to
184 * create boot2, we use an entry point of 0x2000. That entry point is
185 * relative to MEM_USR; thus boot2.bin starts at 0xc000.
187 * The load area and the target area for the client overlap so we have
188 * to use a decrementing string move. We also play segment register
189 * games with the destination address for the move so that the client
190 * can be larger than 16k (which would overflow the zero segment since
191 * the client starts at 0xc000). Relocating BTX is easy since the load
192 * area and target area do not overlap.
194 main.5: mov %dx,MEM_ARG # Save args
195 movb $NSECT,%dh # Sector count
196 movl $1024,%eax # Offset to boot2
197 callw nread.1 # Read disk
198 main.6: mov $MEM_BUF,%si # BTX (before reloc)
199 mov 0xa(%si),%bx # Get BTX length and set
200 mov $NSECT*SIZ_SEC-1,%di # Size of load area (less one)
201 mov %di,%si # End of load
202 add $MEM_BUF,%si # area
203 sub %bx,%di # End of client, 0xc000 rel
204 mov %di,%cx # Size of
206 mov $(MEM_USR+2*SIZ_PAG)>>4,%dx # Segment
207 mov %dx,%es # addressing 0xc000
208 std # Move with decrement
211 mov %ds,%dx # Back to
212 mov %dx,%es # zero segment
213 mov $MEM_BUF,%si # BTX (before reloc)
214 mov $MEM_BTX,%di # BTX
215 mov %bx,%cx # Get BTX length
216 cld # Increment this time
221 * Enable A20 so we can access memory above 1 meg.
222 * Use the zero-valued %cx as a timeout for embedded hardware which do not
223 * have a keyboard controller.
225 seta20: cli # Disable interrupts
226 seta20.1: dec %cx # Timeout?
228 inb $0x64,%al # Get status
229 testb $0x2,%al # Busy?
231 movb $0xd1,%al # Command: Write
232 outb %al,$0x64 # output port
233 seta20.2: inb $0x64,%al # Get status
234 testb $0x2,%al # Busy?
236 movb $0xdf,%al # Enable
238 seta20.3: sti # Enable interrupts
240 jmp start+MEM_JMP-MEM_ORG # Start BTX
244 * Trampoline used to call read from within boot1.
246 nread: xor %eax,%eax # Sector offset in partition
247 nread.1: mov $MEM_BUF,%bx # Transfer buffer
249 addl 0x8(%si),%eax # LBA
253 jnc return # If success, return
254 mov $msg_read,%si # Otherwise, set the error
255 # message and fall through to
258 * Print out the error message pointed to by %ds:(%si) followed
259 * by a prompt, wait for a keypress, and then reboot the machine.
261 error: callw putstr # Display message
262 mov $prompt,%si # Display
263 callw putstr # prompt
264 xorb %ah,%ah # BIOS: Get
266 movw $0x1234, BDA_BOOT # Do a warm boot
267 ljmp $0xffff,$0x0 # reboot the machine
269 * Display a null-terminated string using the BIOS output.
271 putstr.0: mov $0x7,%bx # Page:attribute
272 movb $0xe,%ah # BIOS: Display
273 int $0x10 # character
274 putstr: lodsb # Get char
275 testb %al,%al # End of string?
279 * Overused return code. ereturn is used to return an error from the
280 * read function. Since we assume putstr succeeds, we (ab)use the
281 * same code when we return from putstr.
283 ereturn: movb $0x1,%ah # Invalid
285 return: retw # To caller
287 * Reads sectors from the disk. If EDD is enabled, then check if it is
288 * installed and use it if it is. If it is not installed or not enabled, then
289 * fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
290 * fetch the drive parameters from the BIOS and divide it out ourselves.
293 * %dl - byte - drive number
294 * stack - 10 bytes - EDD Packet
296 read: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
297 jz read.1 # No, use CHS
298 cmpb $0x80,%dl # Hard drive?
299 jb read.1 # No, use CHS
300 mov $0x55aa,%bx # Magic
302 movb $0x41,%ah # BIOS: Check
303 int $0x13 # extensions present
305 jc read.1 # If error, use CHS
306 cmp $0xaa55,%bx # Magic?
307 jne read.1 # No, so use CHS
308 testb $0x1,%cl # Packet interface?
309 jz read.1 # No, so use CHS
310 mov %bp,%si # Disk packet
311 movb $0x42,%ah # BIOS: Extended
315 read.1: push %dx # Save
316 movb $0x8,%ah # BIOS: Get drive
317 int $0x13 # parameters
318 movb %dh,%ch # Max head number
321 andb $0x3f,%cl # Sectors per track
323 cli # Disable interrupts
324 mov 0x8(%bp),%eax # Get LBA
326 movzbl %cl,%ebx # Divide by
327 xor %edx,%edx # sectors
329 movb %ch,%bl # Max head number
330 movb %dl,%ch # Sector number
332 xorb %dl,%dl # number
334 movb %dl,%bh # Head number
336 cmpl $0x3ff,%eax # Cylinder number supportable?
337 sti # Enable interrupts
338 ja ereturn # No, return an error
339 xchgb %al,%ah # Set up cylinder
340 rorb $0x2,%al # number
343 xchg %ax,%cx # number
344 movb %bh,%dh # Head number
345 subb %ah,%al # Sectors this track
346 mov 0x2(%bp),%ah # Blocks to read
347 cmpb %ah,%al # To read
349 #ifdef TRACK_AT_A_TIME
352 movb $1,%al # one sector
354 read.2: mov $0x5,%di # Try count
355 read.3: les 0x4(%bp),%bx # Transfer buffer
357 movb $0x2,%ah # BIOS: Read
358 int $0x13 # from disk
360 jnc read.4 # If success
363 xorb %ah,%ah # BIOS: Reset
364 int $0x13 # disk system
365 xchg %bx,%ax # Block count
366 jmp read.3 # Continue
367 read.4: movzbw %bl,%ax # Sectors read
368 add %ax,0x8(%bp) # Adjust
370 incw 0xa(%bp) # transfer
371 read.5: shlb %bl # buffer
372 add %bl,0x5(%bp) # pointer,
373 sub %al,0x2(%bp) # block count
374 ja read.1 # If not done
375 read.6: retw # To caller
377 read.1: mov $msg_chs,%si
379 msg_chs: .asciz "CHS not supported"
384 msg_read: .asciz "Read"
385 msg_part: .asciz "Boot"
387 prompt: .asciz " error\r\n"
389 flags: .byte FLAGS # Flags
393 /* Partition table */
396 part4: .byte 0x80, 0x00, 0x01, 0x00
397 .byte 0xa5, 0xfe, 0xff, 0xff
398 .byte 0x00, 0x00, 0x00, 0x00
399 .byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
401 .word 0xaa55 # Magic number