DHU man page on 4.4BSD

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

     dhu — DHU-11 communications multiplexer

     device dhu0 at uba0 csr 0160440 vector dhurint dhuxint

     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


     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‐

     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.

     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.


     The dhu driver appeared in 4.3BSD.

4.3 Berkeley Distribution	 June 5, 1993	     4.3 Berkeley Distribution

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