.\" Copyright (c) 1985 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)dhu.4 6.2 (Berkeley) 4/27/86
.TH DHU 4 "April 27, 1986"
dhu \- DHU-11 communications multiplexer
.B "device dhu0 at uba0 csr 0160440 vector dhurint dhuxint"
A DHU-11 provides 16 communication lines.
Each line attached to the DHU-11 communications multiplexer
Input and output for each line may independently
be set to run at any of 13 speeds (50, 200 and 38400 baud are not available);
of flags may be specified for a DHU-11 to say that a line is not properly
connected, and that the line should be treated as hard-wired with carrier
always present. Thus specifying ``flags 0x0004'' in the specification of dhu0
would cause line ttyS2 to be treated in this way.
The DHU-11 driver normally uses input silos
and delays receiver interrupts by 20 milliseconds
rather than taking an interrupt on each input character.
\fBdhu(%d,%d): NXM fault\fR. No response from UNIBUS on a DMA transfer
within a timeout period. This is often followed by a UNIBUS adapter
error. This occurs most frequently when the UNIBUS is heavily loaded
and when devices which hog the bus (such as RK07s) are present.
\fBdhu%d: silo overflow\fR. The character input silo 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 may
then print a message on the console with interrupts disabled.
The driver currently does not make full use of the hardware
capabilities of the DHU-11, for dealing with XON/XOFF flow-control or hard-wired
Although the devices are not the same, a DHU-11 can convince the
DH-11 autoconfiguration code that it is a DH-11.
The 4 40-way cables are a pain.