dhv(4) [bsd man page]

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)

Check Out this Related Man Page

cxa(4) Kernel Interfaces Manual cxa(4)

Name
cxa - CXA16 communications interface

Syntax
device dhu0 at uba0 csr 0160440 flags 0xffff vector dhurint dhuxint

Description
A CXA16 provides 16 data-leads-only communication lines with no modem control. The CXA16 conforms to RS423A. The device behaves and looks
just like a DHV11 (with the exception of modem control and number of lines) and is specified in the configuration line the same as a DHV11
device. Each line attached to the CXA16 communications multiplexer behaves as described in and can be set to run at any of 16 speeds; see
for the encoding.

A flags field of 0xffff must be used to specify that all lines are to operate as hardwired. This is done to prevent the line from being
treated as a modem control line.

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

Diagnostics
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.

Files
See Also
tty(4), MAKEDEV(8)

cxa(4)

Linux and UNIX Man Pages

dhv(4) [bsd man page]

Check Out this Related Man Page