DHV(4)							     Kernel Interfaces Manual							    DHV(4)

NAME

       dhv - DHV-11 communications multiplexer

SYNOPSIS

       /sys/conf/SYSTEM:
	    NDHV dhv_units # DHV11

       /etc/dtab:
	    #Name Unit# Addr   Vector Br Handler(s)	 # Comments
	    dhv   ?	160440 310    5  dhvrint dhvxint # dhv terminal mux

       major device number(s):
	    raw: 24
       minor device encoding:
	    bits 0007 specify line on DHV unit
	    bits 0070 specify DHV unit
	    bit  0100 specifies RTS/CTS (``hardware'') flowcontrol
	    bit  0200 specifies non-blocking open (``CD always on'')

DESCRIPTION

       A DHV-11 provides 8 communication lines.

       Each  line  attached  to the DHV-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 and 200 baud are not available).  While 38400 is available the underlying hardware is not fast
       enough to handle it and there will be pauses/gaps between characters.

       Bit  0200  of  the  minor  device number for DHV 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 in the minor device number via mknod /dev/ttyS2 c 4 194 would enable
       RTS/CTS flow control.

       The DHV-11 has an input silo but does not have the programmable receiver delay that the DHU (and DHQ)  have.   Thus  system  services  more
       interrupts (i.e. gets fewer characters per interrupt on average) with a DHV-11 than with a DHQ (in DHU mode).

FILES

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

SEE ALSO

       tty(4)

DIAGNOSTICS

       dhv%d,%d  NXM.	No  response from QBUS on a DMA transfer within a timeout period.  This error has never been observed on a PDP-11 and is a
       carryover from the VAX driver when that was ported to 2BSD.

       dhv%d diag %o.  Diagnostic information from the DHV11.  This has never been observed.  The DHV-11  hardware  manual  will  be  required	to
       decode the value printed out.

       dhv%d:  %d  overruns.   The  character  input  silo  overflowed before it could be serviced.  This message is printed only when the line is
       closed.	By only printing this when the line is closed further silo overruns are  avoided  (kernel  printf  statements  are  not  interrupt
       driven).

NOTES

       The  DHV lacks the receiver delay that the DHU (and DHQ) have.  Thus it is extremely easy (indeed it's almost certain at higher data rates)
       for a DHV-11 to enter an interrupt per character mode and use 70-80% of the cpu.

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