dhv.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)dhv.4	2.1	3/10/87
.TH dhv 4
.SH Name
dhv \- DHV11 communications interface
.SH Syntax
.B "device dhu0 at uba0 csr 0160440 flags 0x?? vector dhurint dhuxint"
.SH Description
.NXR "DHV11 communications interface"
.NXS "dhv keyword" "DHV11 communications interface"
.NXS "dhu interface" "DHV11 communications interface"
A DHV11 provides eight communication lines with partial modem control,
adequate for UNIX dialup use.
Each line attached to the DHV11 communications interface
behaves as described in
.MS tty 4
and can be set to run at any of 16 speeds.  See
.MS tty 4
for the encoding.
.PP
Bit
.I i
of flags may be specified for a DHV 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 dhu0
would cause line tty02 to be treated in this way.
.PP
The 
.PN dhv
driver normally interrupts on each input character.
.NT
The 
.PN cxa ,
.PN cxb ,
.PN cxy ,
.PN dhv ,
and
.PN dhq
devices operate under the control of the 
.PN dhu
driver.
.NE
.SH Diagnostics
.B "dhu%d: receive fifo overflow"  
.br
The character input fifo overflowed
before it could be serviced.  This can happen if a hard error occurs
when the CPU is running with elevated priority, as the system will
then print a message on the console with interrupts disabled.
This can cause a few input characters to be lost to users.
It is not serious.
.PP
.B "dhu%d:%d DMA ERROR"
.br
A DMA transfer error has occurred.
The
.PN dhv
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.
.PP
.B "dhu%d: DIAG. FAILURE"
.br
This indicates that the
.PN dhv
internal diagnostics have detected an error.
.PP
.B "dhu%d: DHU HARDWARE ERROR.  TX.DMA.START failed"
.br
The 
.PN dhv 
failed to clear the start bit.  Normally,
this is cleared to signal 
that a DMA transfer has completed.
.SH Files
.TP 15
.PN /dev/tty??

.TP
.PN /dev/ttyd?
Dialups
.SH See Also
tty(4), MAKEDEV(8)