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 29, 2006 29.Dt UART 4 30.Os 31.\" 32.Sh NAME 33.Nm uart 34.Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices 35.\" 36.Sh SYNOPSIS 37.Cd "device uart" 38.Pp 39.Cd "device puc" 40.Cd "device uart" 41.Pp 42.Cd "device scc" 43.Cd "device uart" 44.\" 45.Sh DESCRIPTION 46The 47.Nm 48device driver provides support for various classes of UARTs implementing the 49EIA RS-232C (CCITT V.24) serial communications interface. 50Each such interface is controlled by a separate and independent instance of 51the 52.Nm 53driver. 54The primary support for devices that contain multiple serial interfaces or 55that contain other functionality besides one or more serial interfaces is 56provided by the 57.Xr puc 4 , 58or 59.Xr scc 4 60device drivers. 61However, the serial interfaces of those devices that are managed by the 62.Xr puc 4 , 63or 64.Xr scc 4 65driver are each independently controlled by the 66.Nm 67driver. 68As such, the 69.Xr puc 4 , 70or 71.Xr scc 4 72driver provides umbrella functionality for the 73.Nm 74driver and hides the complexities that are inherent when elementary components 75are packaged together. 76.Pp 77The 78.Nm 79driver has a modular design to allow it to be used on differing hardware and 80for various purposes. 81In the following sections the components are discussed in detail. 82Options are described in the section that covers the component to which each 83option applies. 84.\" 85.Ss CORE COMPONENT 86At the heart of the 87.Nm 88driver is the core component. 89It contains the bus attachments and the low-level interrupt handler. 90.\" 91.Ss HARDWARE DRIVERS 92The core component and the kernel interfaces talk to the hardware through the 93hardware interface. 94This interface serves as an abstraction of the hardware and allows varying 95UARTs to be used for serial communications. 96.\" 97.Ss SYSTEM DEVICES 98System devices are UARTs that have a special purpose by way of hardware 99design or software setup. 100For example, Sun UltraSparc machines use UARTs as their keyboard interface. 101Such an UART cannot be used for general purpose communications. 102Likewise, when the kernel is configured for a serial console, the 103corresponding UART will in turn be a system device so that the kernel can 104output boot messages early on in the boot process. 105.\" 106.Ss KERNEL INTERFACES 107The last but not least of the components is the kernel interface. 108This component ultimately determines how the UART is made visible to the 109kernel in particular and to users in general. 110The default kernel interface is the TTY interface. 111This allows the UART to be used for terminals, modems and serial line IP 112applications. 113System devices, with the notable exception of serial consoles, generally 114have specialized kernel interfaces. 115.\" 116.Sh HARDWARE 117The 118.Nm 119driver supports the following classes of UARTs: 120.Pp 121.Bl -bullet -compact 122.It 123NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or 124the 16950 UARTs. 125.It 126SCC: serial communications controllers supported by the 127.Xr scc 4 128device driver. 129.El 130.\" 131.Sh FILES 132.Bl -tag -width ".Pa /dev/ttyu?.init" -compact 133.It Pa /dev/ttyu? 134for callin ports 135.It Pa /dev/ttyu?.init 136.It Pa /dev/ttyu?.lock 137corresponding callin initial-state and lock-state devices 138.Pp 139.It Pa /dev/cuau? 140for callout ports 141.It Pa /dev/cuau?.init 142.It Pa /dev/cuau?.lock 143corresponding callout initial-state and lock-state devices 144.El 145.Sh SEE ALSO 146.Xr puc 4 , 147.Xr scc 4 148.\" 149.Sh HISTORY 150The 151.Nm 152device driver first appeared in 153.Fx 5.2 . 154.Sh AUTHORS 155The 156.Nm 157device driver and this manual page were written by 158.An Marcel Moolenaar Aq marcel@xcllnt.net . 159