uart man page on FreeBSD

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UART(4)			 BSD 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:

     ·	 NS8250: standard hardware based on the 8250, 16450, 16550, 16650,
	 16750 or the 16950 UARTs.
     ·	 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⟩.

BSD				March 12, 2008				   BSD
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