2 .\" Copyright (c) 2003 Marcel Moolenaar
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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"
54 .Bl -tag -compact -width 0x000000
56 device is potential system console
58 use this port for remote kernel debugging
60 set RX FIFO trigger level to ``low'' (NS8250 only)
62 set RX FIFO trigger level to ``medium low'' (NS8250 only)
64 set RX FIFO trigger level to ``medium high'' (default, NS8250 only)
66 set RX FIFO trigger level to ``high'' (NS8250 only)
72 device driver provides support for various classes of UARTs implementing the
73 EIA RS-232C (CCITT V.24) serial communications interface.
74 Each such interface is controlled by a separate and independent instance of
78 The primary support for devices that contain multiple serial interfaces or
79 that contain other functionality besides one or more serial interfaces is
85 However, the serial interfaces of those devices that are managed by the
89 driver are each independently controlled by the
96 driver provides umbrella functionality for the
98 driver and hides the complexities that are inherent when elementary components
99 are packaged together.
103 driver has a modular design to allow it to be used on differing hardware and
104 for various purposes.
105 In the following sections the components are discussed in detail.
106 Options are described in the section that covers the component to which each
112 driver is the core component.
113 It contains the bus attachments and the low-level interrupt handler.
116 The core component and the kernel interfaces talk to the hardware through the
118 This interface serves as an abstraction of the hardware and allows varying
119 UARTs to be used for serial communications.
122 System devices are UARTs that have a special purpose by way of hardware
123 design or software setup.
124 For example, Sun UltraSparc machines use UARTs as their keyboard interface.
125 Such an UART cannot be used for general purpose communications.
126 Likewise, when the kernel is configured for a serial console, the
127 corresponding UART will in turn be a system device so that the kernel can
128 output boot messages early on in the boot process.
130 .Ss KERNEL INTERFACES
131 The last but not least of the components is the kernel interface.
132 This component ultimately determines how the UART is made visible to the
133 kernel in particular and to users in general.
134 The default kernel interface is the TTY interface.
135 This allows the UART to be used for terminals, modems and serial line IP
137 System devices, with the notable exception of serial consoles, generally
138 have specialized kernel interfaces.
143 driver supports the following classes of UARTs:
147 NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or
150 SCC: serial communications controllers supported by the
156 .Bl -tag -width ".Pa /dev/ttyu?.init" -compact
159 .It Pa /dev/ttyu?.init
160 .It Pa /dev/ttyu?.lock
161 corresponding callin initial-state and lock-state devices
165 .It Pa /dev/cuau?.init
166 .It Pa /dev/cuau?.lock
167 corresponding callout initial-state and lock-state devices
176 device driver first appeared in
181 device driver and this manual page were written by
182 .An Marcel Moolenaar Aq marcel@xcllnt.net .