2 .\" Copyright (c) 2003 Marcel Moolenaar
3 .\" All rights reserved.
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33 .Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices
44 .Pa /boot/device.hints :
45 .Cd hint.uart.0.disabled="1"
46 .Cd hint.uart.0.baud="38400"
47 .Cd hint.uart.0.port="0x3f8"
48 .Cd hint.uart.0.flags="0x10"
53 .Bl -tag -compact -width 0x000000
55 device is potential system console
57 use this port for remote kernel debugging
59 set RX FIFO trigger level to ``low'' (NS8250 only)
61 set RX FIFO trigger level to ``medium low'' (NS8250 only)
63 set RX FIFO trigger level to ``medium high'' (default, NS8250 only)
65 set RX FIFO trigger level to ``high'' (NS8250 only)
71 device driver provides support for various classes of UARTs implementing the
72 EIA RS-232C (CCITT V.24) serial communications interface.
73 Each such interface is controlled by a separate and independent instance of
77 The primary support for devices that contain multiple serial interfaces or
78 that contain other functionality besides one or more serial interfaces is
84 However, the serial interfaces of those devices that are managed by the
88 driver are each independently controlled by the
95 driver provides umbrella functionality for the
97 driver and hides the complexities that are inherent when elementary components
98 are packaged together.
102 driver has a modular design to allow it to be used on differing hardware and
103 for various purposes.
104 In the following sections the components are discussed in detail.
105 Options are described in the section that covers the component to which each
111 driver is the core component.
112 It contains the bus attachments and the low-level interrupt handler.
115 The core component and the kernel interfaces talk to the hardware through the
117 This interface serves as an abstraction of the hardware and allows varying
118 UARTs to be used for serial communications.
121 System devices are UARTs that have a special purpose by way of hardware
122 design or software setup.
123 For example, Sun UltraSparc machines use UARTs as their keyboard interface.
124 Such an UART cannot be used for general purpose communications.
125 Likewise, when the kernel is configured for a serial console, the
126 corresponding UART will in turn be a system device so that the kernel can
127 output boot messages early on in the boot process.
129 .Ss KERNEL INTERFACES
130 The last but not least of the components is the kernel interface.
131 This component ultimately determines how the UART is made visible to the
132 kernel in particular and to users in general.
133 The default kernel interface is the TTY interface.
134 This allows the UART to be used for terminals, modems and serial line IP
136 System devices, with the notable exception of serial consoles, generally
137 have specialized kernel interfaces.
142 driver supports the following classes of UARTs:
146 NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or
149 SCC: serial communications controllers supported by the
155 .Bl -tag -width ".Pa /dev/ttyu?.init" -compact
158 .It Pa /dev/ttyu?.init
159 .It Pa /dev/ttyu?.lock
160 corresponding callin initial-state and lock-state devices
164 .It Pa /dev/cuau?.init
165 .It Pa /dev/cuau?.lock
166 corresponding callout initial-state and lock-state devices
175 device driver first appeared in
180 device driver and this manual page were written by
181 .An Marcel Moolenaar Aq marcel@xcllnt.net .