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 August 10, 2015 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.Pp 50With 51.Ar flags 52encoded as: 53.Bl -tag -compact -width 0x000000 54.It 0x00010 55device is potential system console 56.It 0x00080 57use this port for remote kernel debugging 58.It 0x00100 59set RX FIFO trigger level to ``low'' (NS8250 only) 60.It 0x00200 61set RX FIFO trigger level to ``medium low'' (NS8250 only) 62.It 0x00400 63set RX FIFO trigger level to ``medium high'' (default, NS8250 only) 64.It 0x00800 65set RX FIFO trigger level to ``high'' (NS8250 only) 66.El 67.\" 68.Sh DESCRIPTION 69The 70.Nm 71device driver provides support for various classes of UARTs implementing the 72EIA RS-232C (CCITT V.24) serial communications interface. 73Each such interface is controlled by a separate and independent instance of 74the 75.Nm 76driver. 77The primary support for devices that contain multiple serial interfaces or 78that contain other functionality besides one or more serial interfaces is 79provided by the 80.Xr puc 4 , 81or 82.Xr scc 4 83device drivers. 84However, the serial interfaces of those devices that are managed by the 85.Xr puc 4 , 86or 87.Xr scc 4 88driver are each independently controlled by the 89.Nm 90driver. 91As such, the 92.Xr puc 4 , 93or 94.Xr scc 4 95driver provides umbrella functionality for the 96.Nm 97driver and hides the complexities that are inherent when elementary components 98are packaged together. 99.Pp 100The 101.Nm 102driver has a modular design to allow it to be used on differing hardware and 103for various purposes. 104In the following sections the components are discussed in detail. 105Options are described in the section that covers the component to which each 106option applies. 107.\" 108.Ss CORE COMPONENT 109At the heart of the 110.Nm 111driver is the core component. 112It contains the bus attachments and the low-level interrupt handler. 113.\" 114.Ss HARDWARE DRIVERS 115The core component and the kernel interfaces talk to the hardware through the 116hardware interface. 117This interface serves as an abstraction of the hardware and allows varying 118UARTs to be used for serial communications. 119.\" 120.Ss SYSTEM DEVICES 121System devices are UARTs that have a special purpose by way of hardware 122design or software setup. 123For example, Sun UltraSparc machines use UARTs as their keyboard interface. 124Such an UART cannot be used for general purpose communications. 125Likewise, when the kernel is configured for a serial console, the 126corresponding UART will in turn be a system device so that the kernel can 127output boot messages early on in the boot process. 128.\" 129.Ss KERNEL INTERFACES 130The last but not least of the components is the kernel interface. 131This component ultimately determines how the UART is made visible to the 132kernel in particular and to users in general. 133The default kernel interface is the TTY interface. 134This allows the UART to be used for terminals, modems and serial line IP 135applications. 136System devices, with the notable exception of serial consoles, generally 137have specialized kernel interfaces. 138.\" 139.Sh HARDWARE 140The 141.Nm 142driver supports the following classes of UARTs: 143.Pp 144.Bl -bullet -compact 145.It 146NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or 147the 16950 UARTs. 148.It 149SCC: serial communications controllers supported by the 150.Xr scc 4 151device driver. 152.El 153.\" 154.Sh Pulse Per Second (PPS) Timing Interface 155The 156.Nm 157driver can capture PPS timing information as defined in RFC 2783. 158The API, accessed via 159.Xr ioctl 8 , 160is available on the tty device. 161To use the PPS capture feature with 162.Xr ntpd 8 , 163symlink the tty device to 164.Va /dev/pps0. 165.Pp 166The 167.Va hw.uart.pps_mode 168tunable configures the PPS capture mode for all uart devices; 169it can be set in 170.Xr loader.conf 5 . 171The 172.Va dev.uart.0.pps_mode 173sysctl configures the PPS capture mode for a specific uart device; 174it can be set in 175.Xr loader.conf 5 176or 177.Xr sysctl.conf 5 . 178The following capture modes are available: 179.Bl -tag -compact -offset "mmmm" -width "mmmm" 180.It 0 181Capture disabled. 182.It 1 183Capture pulses on the CTS line. 184.It 2 185Capture pulses on the DCD line (default). 186.El 187.Sh FILES 188.Bl -tag -width ".Pa /dev/ttyu?.init" -compact 189.It Pa /dev/ttyu? 190for callin ports 191.It Pa /dev/ttyu?.init 192.It Pa /dev/ttyu?.lock 193corresponding callin initial-state and lock-state devices 194.Pp 195.It Pa /dev/cuau? 196for callout ports 197.It Pa /dev/cuau?.init 198.It Pa /dev/cuau?.lock 199corresponding callout initial-state and lock-state devices 200.El 201.Sh SEE ALSO 202.Xr puc 4 , 203.Xr scc 4 204.\" 205.Sh HISTORY 206The 207.Nm 208device driver first appeared in 209.Fx 5.2 . 210.Sh AUTHORS 211The 212.Nm 213device driver and this manual page were written by 214.An Marcel Moolenaar Aq Mt marcel@xcllnt.net . 215