dhu man page on 4.4BSD

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DHU(4)		       BSD/vax Kernel Interfaces Manual			DHU(4)

NAME
     dhu — DHU-11 communications multiplexer

SYNOPSIS
     device dhu0 at uba0 csr 0160440 vector dhurint dhuxint

DESCRIPTION
     A DHU-11 provides 16 communication lines.

     An optional argument flags may be supplied with the device specification
     in the config file indicating that the line corresponding to bit number i
     is not properly connected, and should be treated as hard-wired with car‐
     rier always present.  Thus specifying ‘flags 0x0004’ for dhu0 would cause
     line ttyS2 to be treated in this way.

     Normal I/O control parameters for individual lines are managed by
     ioctl(2) calls.  Individual DHU-11 lines may be configured to run at any
     of 13 speeds (50, 200 and 38400 baud are not available); the speed may be
     set via getty(8) or stty(1) or may be communicated by other programs
     which utilize ioctl such as ifcongif(8), see tty(4).

     The DHU-11 driver normally uses input silos and delays receiver inter‐
     rupts by 20 milliseconds rather than taking an interrupt on each input
     character.

FILES
     /dev/tty[S-Z][0-9a-f]

DIAGNOSTICS
     dhu(%d,%d): NXM fault.  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 seri‐
     ous.

     dhu%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 running with elevated priority, as the system may then print a message
     on the console with interrupts disabled.

NOTES
     The driver currently does not make full use of the hardware capabilities
     of the DHU-11, for dealing with XON/XOFF flow-control or hard-wired lines
     for example.

     Although the devices are not the same, a DHU-11 can convince the DH-11
     autoconfiguration code that it is a DH-11.

     The 4 40-way cables are a pain.

SEE ALSO
     tty(4)

HISTORY
     The dhu driver appeared in 4.3BSD.

4.3 Berkeley Distribution	 June 5, 1993	     4.3 Berkeley Distribution
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