xref: /freebsd/share/man/man4/uart.4 (revision 6fd05b64b5b65dd4ba9b86482a0634a5f0b96c29)
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 25, 2003
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.\"
42.Sh DESCRIPTION
43The
44.Nm
45device driver provides support for various classes of UARTs implementing the
46EIA RS-232C (CCITT V.24) serial communications interface.
47Each such interface is controlled by a separate and independent instance of
48the
49.Nm
50driver.
51The primary support for devices that contain multiple serial interfaces or
52that contain other functionality besides one or more serial interfaces is
53provided by the
54.Xr puc 4
55device driver.
56However, the serial interfaces of those devices that are managed by the
57.Xr puc 4
58driver are controlled by the
59.Nm
60driver.
61As such, the
62.Xr puc 4
63driver provides umbrella functionality for the
64.Nm
65driver and hides the complexities that are inherent when elementary components
66are packaged together.
67.Pp
68The
69.Nm
70driver has a modular design to allow it to be used on differing hardware and
71for various purposes.
72In the following sections the components are discussed in detail.
73Options are described in the section that covers the component to which each
74option applies.
75.\"
76.Ss CORE COMPONENT
77At the heart of the
78.Nm
79driver is the core component.
80It contains the bus attachments and the low-level interrupt handler.
81.\"
82.Ss HARDWARE DRIVERS
83The core component and the kernel interfaces talk to the hardware through the
84hardware interface.
85This interface serves as an abstraction of the hardware and allows varying
86UARTs to be used for serial communications.
87.\"
88.Ss SYSTEM DEVICES
89System devices are UARTs that have a special purpose by way of hardware
90design or software setup.
91For example, Sun UltraSparc machines use UARTs as their keyboard interface.
92Such an UART cannot be used for general purpose communications.
93Likewise, when the kernel is configured for a serial console, the
94corresponding UART will in turn be a system device so that the kernel can
95output boot messages early on in the boot process.
96.\"
97.Ss KERNEL INTERFACES
98The last but not least of the components is the kernel interface.
99This component ultimately determines how the UART is made visible to the
100kernel in particular and to users in general.
101The default kernel interface is the TTY interface.
102This allows the UART to be used for terminals, modems and serial line IP
103applications.
104System devices, with the notable exception of serial consoles, generally
105have specialized kernel interfaces.
106.\"
107.Sh SEE ALSO
108.Xr puc 4
109.\"
110.Sh HISTORY
111The
112.Nm
113device driver first appeared in
114.Fx 5.2 .
115.Sh AUTHORS
116This manual page was written by
117.An Marcel Moolenaar Aq marcel@xcllnt.net .
118