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BSD 2.11 - man page for dhv (bsd section 4)

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DHV(4)											   DHV(4)

       dhv - DHV-11 communications multiplexer

	    NDHV dhv_units # DHV11

	    #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'')

       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 independently be set  to  run  at  any  of  13
       speeds (50 and 200 baud are not available).  While 38400 is available the underlying hard-
       ware 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).



       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

       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)
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