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dhv(4) [bsd man page]

DHV(4)							     Kernel Interfaces Manual							    DHV(4)

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
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)

Check Out this Related Man Page

cxy(4)							     Kernel Interfaces Manual							    cxy(4)

       cxy - CXY08 communications interface

       device dhu0 at uba0 csr 0160440 flags 0x?? vector dhurint dhuxint

       A  CXY08 provides eight communication lines with modem control adequate for UNIX dialup use. The device behaves and looks just like a DHV11
       and is specified in the configuration line the same as a DHV11 device.  Each line attached to the CXY08 communications interface behaves as
       described in and can be set to run at any of 16 speeds. See for the encoding.

       Bit  i of flags can be specified for a device to say that a line is not properly connected and that the line should be treated as hardwired
       with carrier always present.  Thus, specifying flags 0x04 in the specification of would cause line tty02 to be treated in this way.

       The driver normally interrupts on each input character.	The and devices operate under the control of the driver.

       dhu%d: receive fifo overflow
       The character input fifo overflowed before it could be serviced.  This can happen if a hard error occurs when the CPU is running with  ele-
       vated  priority,  as the system then prints a message on the console with interrupts disabled.  This can cause a few input characters to be
       lost to users.  It is not serious.

       dhu%d:%d DMA ERROR
       A DMA transfer error has occurred.  The unit number and line number are printed.  This means that  the  channel	indicated  has	failed	to
       transfer  DMA data within 10.7 microseconds of the bus request being acknowledged or that there is a memory parity error.  This may cause a
       few output characters to be lost.

       dhu%d: DIAG. FAILURE
       This indicates that the internal diagnostics have detected an error.

       dhu%d: DHU HARDWARE ERROR.  TX.DMA.START failed
       The failed to clear the start bit.  Normally, this is cleared to signal that a DMA transfer has completed.


See Also
       tty(4), MAKEDEV(8)


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