2.11BSD#431 - /usr/man/cat4/dhu.0

DHU(4)		    UNIX Programmer's Manual		   DHU(4)


NAME
     dhu - DHU-11 communications multiplexer

SYNOPSIS
     /sys/conf/SYSTEM:
	  NDHU dhu_units # DHU11

     /etc/dtab:
	  #Name Unit# Addr   Vector Br Handler(s)      # Comments
	  du	?     160020 310    5  dhurint dhuxint # dhu11 terminal mux

     major device number(s):
	  raw: 4
     minor device encoding:
	  bits 0017 specify line on DHU unit
	  bits 0060 specify DHU unit
	  bit  0100 specify RTS/CTS flow control
	  bit  0200 specifies non-blocking open (``CD always on'')

DESCRIPTION
     A DHU-11 provides 16 communication lines.

     Each line attached to the DHU-11 communications multiplexer
     behaves as described in tty(4).  Input and output for each
     line may independently be set to run at any of 13 speeds
     (50, 200 and 38400 baud are not available); see tty(4) for
     the encoding.

     Bit 0200 of the minor device number for DHU lines may be set
     to say that a line is not properly connected, and that the
     line should be treated as hard-wired with carrier always
     present.  Thus creating the special character device node
     "4, 130" via mknod /dev/ttyS2 c 4 130 would cause line ttyS2
     to be treated in this way.  Turning on bit 6 (adding 64) to
     the minor device number via mknod /dev/ttyS2 c 4 194 enables
     RTS/CTS flow control.

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

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

SEE ALSO
     tty(4)

DIAGNOSTICS
     dhu(%d,%d) NXM.  No response from UNIBUS on a DMA transfer
     within a timeout period.  This has never been observed on a
     PDP-11 and is believed to be a carryover from the VAX driver
     when it was ported.  It is not serious.


Printed 11/26/99	  May 31, 1997				1


DHU(4)		    UNIX Programmer's Manual		   DHU(4)


     dhu%d %d overruns.  The character input silo overflowed
     before it could be serviced.  This message is printed only
     at line close time rather than on each overrun error.  Ker-
     nel printf's are not interrupt driven and caused more over-
     runs by blocking interrupts for lengthy periods of time.

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.

     The 4 40-way cables are a pain.


Printed 11/26/99	  May 31, 1997				2