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UART(4)		       FreeBSD Kernel Interfaces Manual		       UART(4)

NAME
     uart -- driver for	Universal Asynchronous Receiver/Transmitter (UART)
     devices

SYNOPSIS
     device uart

     device puc
     device uart

     device scc
     device uart

     In	/boot/device.hints:
     hint.uart.0.disabled="1"
     hint.uart.0.baud="38400"
     hint.uart.0.port="0x3f8"
     hint.uart.0.flags="0x10"

     With flags	encoded	as:
     0x00010   device is potential system console
     0x00080   use this	port for remote	kernel debugging
     0x00100   set RX FIFO trigger level to ``low'' (NS8250 only)
     0x00200   set RX FIFO trigger level to ``medium low'' (NS8250 only)
     0x00400   set RX FIFO trigger level to ``medium high'' (default, NS8250
	       only)
     0x00800   set RX FIFO trigger level to ``high'' (NS8250 only)

DESCRIPTION
     The uart device driver provides support for various classes of UARTs
     implementing the EIA RS-232C (CCITT V.24) serial communications inter-
     face.  Each such interface	is controlled by a separate and	independent
     instance of the uart driver.  The primary support for devices that	con-
     tain multiple serial interfaces or	that contain other functionality
     besides one or more serial	interfaces is provided by the puc(4), or
     scc(4) device drivers.  However, the serial interfaces of those devices
     that are managed by the puc(4), or	scc(4) driver are each independently
     controlled	by the uart driver.  As	such, the puc(4), or scc(4) driver
     provides umbrella functionality for the uart driver and hides the com-
     plexities 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 sections the compo-
     nents 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 abstraction of the
     hardware and allows varying UARTs to be used for serial communications.

   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.

   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 ker-
     nel 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 inter-
     faces.

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	 SCC: serial communications controllers	supported by the scc(4)	device
	 driver.

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), scc(4)

HISTORY
     The uart device driver first appeared in FreeBSD 5.2.

AUTHORS
     The uart device driver and	this manual page were written by Marcel
     Moolenaar <marcel@xcllnt.net>.

FreeBSD	10.1			March 12, 2008			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | HARDWARE | FILES | SEE ALSO | HISTORY | AUTHORS

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