2 .\" Copyright (c) 2003 Marcel Moolenaar
3 .\" All rights reserved.
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34 .Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices
45 .Bd -ragged offset -compact
47 .Pa /boot/device.hints :
48 .Cd hint.uart.0.disabled="1"
49 .Cd hint.uart.0.baud="38400"
50 .Cd hint.uart.0.port="0x3f8"
51 .Cd hint.uart.0.flags="0x10"
57 .Bl -tag -compact -width 0x000000
59 device is potential system console
61 use this port for remote kernel debugging
63 set RX FIFO trigger level to ``low'' (NS8250 only)
65 set RX FIFO trigger level to ``medium low'' (NS8250 only)
67 set RX FIFO trigger level to ``medium high'' (default, NS8250 only)
69 set RX FIFO trigger level to ``high'' (NS8250 only)
75 device driver provides support for various classes of UARTs implementing the
76 EIA RS-232C (CCITT V.24) serial communications interface.
77 Each such interface is controlled by a separate and independent instance of
81 The primary support for devices that contain multiple serial interfaces or
82 that contain other functionality besides one or more serial interfaces is
88 However, the serial interfaces of those devices that are managed by the
92 driver are each independently controlled by the
99 driver provides umbrella functionality for the
101 driver and hides the complexities that are inherent when elementary components
102 are packaged together.
106 driver has a modular design to allow it to be used on differing hardware and
107 for various purposes.
108 In the following sections the components are discussed in detail.
109 Options are described in the section that covers the component to which each
115 driver is the core component.
116 It contains the bus attachments and the low-level interrupt handler.
119 The core component and the kernel interfaces talk to the hardware through the
121 This interface serves as an abstraction of the hardware and allows varying
122 UARTs to be used for serial communications.
125 System devices are UARTs that have a special purpose by way of hardware
126 design or software setup.
127 For example, Sun UltraSparc machines use UARTs as their keyboard interface.
128 Such an UART cannot be used for general purpose communications.
129 Likewise, when the kernel is configured for a serial console, the
130 corresponding UART will in turn be a system device so that the kernel can
131 output boot messages early on in the boot process.
133 .Ss KERNEL INTERFACES
134 The last but not least of the components is the kernel interface.
135 This component ultimately determines how the UART is made visible to the
136 kernel in particular and to users in general.
137 The default kernel interface is the TTY interface.
138 This allows the UART to be used for terminals, modems and serial line IP
140 System devices, with the notable exception of serial consoles, generally
141 have specialized kernel interfaces.
146 driver supports the following classes of UARTs:
150 NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or
153 SCC: serial communications controllers supported by the
159 .Bl -tag -width ".Pa /dev/ttyu?.init" -compact
162 .It Pa /dev/ttyu?.init
163 .It Pa /dev/ttyu?.lock
164 corresponding callin initial-state and lock-state devices
168 .It Pa /dev/cuau?.init
169 .It Pa /dev/cuau?.lock
170 corresponding callout initial-state and lock-state devices
179 device driver first appeared in
184 device driver and this manual page were written by
185 .An Marcel Moolenaar Aq marcel@xcllnt.net .