DH(4)                  OpenBSD Programmer's Manual (VAX)                 DH(4)

NAME
     dh - DH-11/ DM-11 multiplexer device interface

SYNOPSIS
     device dh0 at uba0 csr 0160020 vector dhrint dhxint [flags]
     device dm0 at uba0 csr 0170500 vector dmintr [flags]

DESCRIPTION
     A DH-11 provides 16 serial communication lines; DM-11s may optionally be
     paired with DH-11s to provide modem control for the lines.

     An optional argument flags may be supplied with the device specification
     in the config(8) file indicating that the line corresponding to bit num-
     ber i is not properly connected, and should be treated as hard-wired with
     carrier always present.  Thus specifying `flags 0x0004' for dh0 would
     cause line ttyh2 to be treated in this way.

     Normal I/O control parameters for individual lines are managed by
     ioctl(2) calls.  Line speeds may be initiated via getty(8) and stty(1) or
     may be communicated by other programs which utilize ioctl(2) such as
     ifconfig(8), see tty(4).

     The dh driver monitors the rate of input on each board, and switches be-
     tween the use of character-at-a-time interrupts and input silos.  While
     the silo is enabled during periods of high-speed input, the driver polls
     for input 30 times per second.

FILES
     /dev/tty[h-o][0-9a-f]
     /dev/ttyd[0-9a-f]

DIAGNOSTICS
     dh%d: NXM.  No response from UNIBUS on a dma transfer within a timeout
     period.  This is often followed by a UNIBUS adapter error.  This occurs
     most frequently when the UNIBUS is heavily loaded and when devices which
     hog the bus (such as RK07s) are present. It is not serious.

     dh%d: silo overflow.  The character input silo overflowed before it could
     be serviced.  This can happen if a hard error occurs when the CPU is run-
     ning with elevated priority, as the system will then print a message on
     the console with interrupts disabled.  It is not serious.

SEE ALSO
     tty(4)

HISTORY
     A dh driver appeared in Version 6 AT&T UNIX.

OpenBSD 3.0                     March 27, 1991                               1
