1.\" 2.\" Copyright (c) 2003 Marcel Moolenaar 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd March 12, 2008 29.Dt UART 4 30.Os 31.Sh NAME 32.Nm uart 33.Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices 34.Sh SYNOPSIS 35.Cd "device uart" 36.Pp 37.Cd "device puc" 38.Cd "device uart" 39.Pp 40.Cd "device scc" 41.Cd "device uart" 42.Pp 43In 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" 49.Ed 50.Pp 51With 52.Ar flags 53encoded as: 54.Bl -tag -compact -width 0x000000 55.It 0x00010 56device is potential system console 57.It 0x00080 58use this port for remote kernel debugging 59.It 0x00100 60set RX FIFO trigger level to ``low'' (NS8250 only) 61.It 0x00200 62set RX FIFO trigger level to ``medium low'' (NS8250 only) 63.It 0x00400 64set RX FIFO trigger level to ``medium high'' (default, NS8250 only) 65.It 0x00800 66set RX FIFO trigger level to ``high'' (NS8250 only) 67.El 68.\" 69.Sh DESCRIPTION 70The 71.Nm 72device driver provides support for various classes of UARTs implementing the 73EIA RS-232C (CCITT V.24) serial communications interface. 74Each such interface is controlled by a separate and independent instance of 75the 76.Nm 77driver. 78The primary support for devices that contain multiple serial interfaces or 79that contain other functionality besides one or more serial interfaces is 80provided by the 81.Xr puc 4 , 82or 83.Xr scc 4 84device drivers. 85However, the serial interfaces of those devices that are managed by the 86.Xr puc 4 , 87or 88.Xr scc 4 89driver are each independently controlled by the 90.Nm 91driver. 92As such, the 93.Xr puc 4 , 94or 95.Xr scc 4 96driver provides umbrella functionality for the 97.Nm 98driver and hides the complexities that are inherent when elementary components 99are packaged together. 100.Pp 101The 102.Nm 103driver has a modular design to allow it to be used on differing hardware and 104for various purposes. 105In the following sections the components are discussed in detail. 106Options are described in the section that covers the component to which each 107option applies. 108.\" 109.Ss CORE COMPONENT 110At the heart of the 111.Nm 112driver is the core component. 113It contains the bus attachments and the low-level interrupt handler. 114.\" 115.Ss HARDWARE DRIVERS 116The core component and the kernel interfaces talk to the hardware through the 117hardware interface. 118This interface serves as an abstraction of the hardware and allows varying 119UARTs to be used for serial communications. 120.\" 121.Ss SYSTEM DEVICES 122System devices are UARTs that have a special purpose by way of hardware 123design or software setup. 124For example, Sun UltraSparc machines use UARTs as their keyboard interface. 125Such an UART cannot be used for general purpose communications. 126Likewise, when the kernel is configured for a serial console, the 127corresponding UART will in turn be a system device so that the kernel can 128output boot messages early on in the boot process. 129.\" 130.Ss KERNEL INTERFACES 131The last but not least of the components is the kernel interface. 132This component ultimately determines how the UART is made visible to the 133kernel in particular and to users in general. 134The default kernel interface is the TTY interface. 135This allows the UART to be used for terminals, modems and serial line IP 136applications. 137System devices, with the notable exception of serial consoles, generally 138have specialized kernel interfaces. 139.\" 140.Sh HARDWARE 141The 142.Nm 143driver supports the following classes of UARTs: 144.Pp 145.Bl -bullet -compact 146.It 147NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or 148the 16950 UARTs. 149.It 150SCC: serial communications controllers supported by the 151.Xr scc 4 152device driver. 153.El 154.\" 155.Sh FILES 156.Bl -tag -width ".Pa /dev/ttyu?.init" -compact 157.It Pa /dev/ttyu? 158for callin ports 159.It Pa /dev/ttyu?.init 160.It Pa /dev/ttyu?.lock 161corresponding callin initial-state and lock-state devices 162.Pp 163.It Pa /dev/cuau? 164for callout ports 165.It Pa /dev/cuau?.init 166.It Pa /dev/cuau?.lock 167corresponding callout initial-state and lock-state devices 168.El 169.Sh SEE ALSO 170.Xr puc 4 , 171.Xr scc 4 172.\" 173.Sh HISTORY 174The 175.Nm 176device driver first appeared in 177.Fx 5.2 . 178.Sh AUTHORS 179The 180.Nm 181device driver and this manual page were written by 182.An Marcel Moolenaar Aq marcel@xcllnt.net . 183