1DHV(4)                     Kernel Interfaces Manual                     DHV(4)
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NAME

6       dhv - DHV-11 communications multiplexer
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SYNOPSIS

9       /sys/conf/SYSTEM:
10            NDHV dhv_units # DHV11
11
12       /etc/dtab:
13            #Name Unit# Addr   Vector Br Handler(s)      # Comments
14            dhv   ?     160440 310    5  dhvrint dhvxint # dhv terminal mux
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16       major device number(s):
17            raw: 24
18       minor device encoding:
19            bits 0007 specify line on DHV unit
20            bits 0070 specify DHV unit
21            bit  0100 specifies RTS/CTS (``hardware'') flowcontrol
22            bit  0200 specifies non-blocking open (``CD always on'')
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DESCRIPTION

25       A DHV-11 provides 8 communication lines.
26
27       Each  line attached to the DHV-11 communications multiplexer behaves as
28       described in tty(4).  Input and output for each line may  independently
29       be  set to run at any of 13 speeds (50 and 200 baud are not available).
30       While 38400 is available the underlying hardware is not fast enough  to
31       handle it and there will be pauses/gaps between characters.
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33       Bit  0200  of  the  minor device number for DHV lines may be set to say
34       that a line is not properly connected, and  that  the  line  should  be
35       treated  as  hard-wired with carrier always present.  Thus creating the
36       special character device node "4, 130" via mknod  /dev/ttyS2  c  4  130
37       would  cause line ttyS2 to be treated in this way.  Turning on bit 6 in
38       the minor device number via mknod  /dev/ttyS2  c  4  194  would  enable
39       RTS/CTS flow control.
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41       The  DHV-11  has  an  input  silo  but  does  not have the programmable
42       receiver delay that the DHU (and DHQ) have.  Thus system services  more
43       interrupts (i.e. gets fewer characters per interrupt on average) with a
44       DHV-11 than with a DHQ (in DHU mode).
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FILES

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

50       tty(4)
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DIAGNOSTICS

53       dhv%d,%d NXM.  No response from QBUS on a DMA transfer within a timeout
54       period.  This error has never been observed on a PDP-11 and is a carry‐
55       over from the VAX driver when that was ported to 2BSD.
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57       dhv%d diag %o.  Diagnostic information from the DHV11.  This has  never
58       been  observed.   The DHV-11 hardware manual will be required to decode
59       the value printed out.
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61       dhv%d: %d overruns.  The character  input  silo  overflowed  before  it
62       could  be  serviced.   This  message  is  printed only when the line is
63       closed.  By only printing this when the line  is  closed  further  silo
64       overruns  are  avoided  (kernel  printf  statements  are  not interrupt
65       driven).
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NOTES

68       The DHV lacks the receiver delay that the DHU (and DHQ) have.  Thus  it
69       is extremely easy (indeed it's almost certain at higher data rates) for
70       a DHV-11 to enter an interrupt per character mode and use 70-80% of the
71       cpu.
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753rd Berkeley Distribution        May 31, 1997                           DHV(4)