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



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


      device uart
      device puc
      device uart
      device scc
      device uart


      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
      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.
      At the heart of the uart driver is the core component.  It contains the
      bus attachments and the low-level interrupt handler.
      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 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.
      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‐


      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


      /dev/ttyu?       for callin ports
      /dev/ttyu?.lock  corresponding callin initial-state and lock-state
      /dev/cuau?       for callout ports
      /dev/cuau?.lock  corresponding callout initial-state and lock-state
      puc(4), scc(4)


      The uart device driver first appeared in FreeBSD 5.2.


      The uart device driver and this manual page were written by Marcel
      Moolenaar 〈〉.


Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.