uart(4)

NAME

uart - driver for Universal Asynchronous Receiver/Transmit

ter (UART)
devices

SYNOPSIS

device uart
device puc
device uart

DESCRIPTION

The uart device driver provides support for various classes

of UARTs
implementing the EIA RS-232C (CCITT V.24) serial communica

tions interface. Each such interface is controlled by a separate and

independent
instance of the uart driver. The primary support for de

vices that contain multiple serial interfaces or that contain other func

tionality
besides one or more serial interfaces is provided by the

puc(4) device
driver. However, the serial interfaces of those devices

that are managed
by the puc(4) driver are controlled by the uart driver. As

such, the
puc(4) driver provides umbrella functionality for the uart

driver and
hides the complexities that are inherent when elementary

components are
packaged together.

The uart driver has a modular design to allow it to be used

on differing
hardware and for various purposes. In the following sec

tions the components are discussed in detail. Options are described in the

section that
covers the component to which each option applies.

CORE COMPONENT

At the heart of the uart driver is the core component. It

contains the
bus attachments and the low-level interrupt handler.

HARDWARE DRIVERS

The core component and the kernel interfaces talk to the

hardware through
the hardware interface. This interface serves as an ab

straction of the
hardware and allows varying UARTs to be used for serial com

munications.

SYSTEM DEVICES

System devices are UARTs that have a special purpose by way

of hardware
design or software setup. For example, Sun UltraSparc ma

chines use UARTs
as their keyboard interface. Such an UART cannot be used

for general
purpose communications. Likewise, when the kernel is con

figured 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.

KERNEL INTERFACES

The last but not least of the components is the kernel in

terface. This
component ultimately determines how the UART is made visible

to the kernel in particular and to users in general. The default ker

nel 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.

HARDWARE

The uart driver supports the following classes of UARTs:

+o NS8250: standard hardware based on the 8250, 16450,

16550, 16650,

16750 or the 16950 UARTs

+o SAB82532: Siemens SAB 82532 based serial communications

controllers

in asynchronuous mode.

+o Z8530: Zilog 8530 based serial communications con

trollers in asyn

chronuous mode.

FILES

/dev/ttyu? for callin ports
/dev/ttyu?.init
/dev/ttyu?.lock corresponding callin initial-state and

lock-state

devices

/dev/cuau? for callout ports
/dev/cuau?.init
/dev/cuau?.lock corresponding callout initial-state and

lock-state

devices

SEE ALSO

puc(4)

HISTORY

The uart device driver first appeared in FreeBSD 5.2.

AUTHORS

This manual page was written by Marcel Moolenaar <mar

cel@xcllnt.net>.

BSD August 25, 2003

BSD