xref: /freebsd/share/man/man4/uart.4 (revision 27d5dc189c8e2eaf1cbe7e47078bf065854ba210)

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.\" Copyright (c) 2003 Marcel Moolenaar
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.\" $FreeBSD$
.\"
.Dd August 25, 2003
.Dt UART 4
.Os
.\"
.Sh NAME
.Nm uart
.Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices
.\"
.Sh SYNOPSIS
.Cd "device uart"
.Pp
.Cd "device puc"
.Cd "device uart"
.Pp
.\"
.Sh DESCRIPTION
The
.Nm
device driver provides support for various classes of UARTs implementing the
EIA RS-232C (CCITT V.24) serial communications interface.
Each such interface is controlled by a seperate and independent instance of
the
.Nm
driver.
The primary support for devices that contain multiple serial interfaces or
that contain other functionality besides one or more serial interfaces is
provided by the
.Xr puc 4
device driver.
However, the serial interfaces of those devices that are managed by the
.Xr puc 4
driver are controlled by the
.Nm
driver.
As such, the
.Xr puc 4
driver provides umbrella functionality for the
.Nm
driver and hides the complexities that are inherent when elementary components
are packaged together.
.Pp
The
.Nm
driver has a modular design to allow it to be used on differing hardware and
for various purposes.
In the following sections the components are discussed in detail.
Options are described in the section that covers the component to which each
option applies.
.\"
.Ss CORE COMPONENT
At the heart of the
.Nm
driver is the core component. It contains the bus attachments and the low-level
interrupt handler.
.\"
.Ss HARDWARE DRIVERS
The core component and the kernel interfaces talk to the hardware through the
hardware interface.
This interface serves as an abstraction of the hardware and allows varying
UARTs to be used for serial communications.
.\"
.Ss SYSTEM DEVICES
System devices are UARTs that have a special purpose by way of hardware
design or software setup.
For example, Sun UltraSparc machines use UARTs as their keyboard interface.
Such an UART cannot be used for general purpose communications.
Likewise, when the kernel is configured for a serial console, the
corresponding UART will in turn be a system device so that the kernel can
output boot messages early on in the boot process.
.\"
.Ss KERNEL INTERFACES
The last but not least of the components is the kernel interface.
This component ultimately determines how the UART is made visible to the
kernel in particular and to users in general.
The default kernel interface is the TTY interface.
This allows the UART to be used for terminals, modems and serial line IP
applications.
System devices, with the notable exception of serial consoles, generally
have specialized kernel interfaces.
.\"
.Sh SEE ALSO
.Xr puc 4
.\"
.Sh HISTORY
The
.Nm
device driver first appeared in
.Fx 5.2 .