bsd man page for dhu

DHU(4)							     Kernel Interfaces 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 indepen-
       dently 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.

       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.  Kernel printf's are not interrupt driven and caused more overruns 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.

3rd Berkeley Distribution					   May 31, 1997 							    DHU(4)