DHU(4) BSD/vax Kernel Interfaces Manual DHU(4)NAMEdhu — DHU-11 communications multiplexer
device dhu0 at uba0 csr 0160440 vector dhurint dhuxint
A DHU-11 provides 16 communication lines.
An optional argument flags may be supplied with the device specification
in the config file indicating that the line corresponding to bit number i
is not properly connected, and should be treated as hard-wired with car‐
rier always present. Thus specifying ‘flags 0x0004’ for dhu0 would cause
line ttyS2 to be treated in this way.
Normal I/O control parameters for individual lines are managed by
ioctl(2) calls. Individual DHU-11 lines may be configured to run at any
of 13 speeds (50, 200 and 38400 baud are not available); the speed may be
set via getty(8) or stty(1) or may be communicated by other programs
which utilize ioctl such as ifcongif(8), see tty(4).
The DHU-11 driver normally uses input silos and delays receiver inter‐
rupts by 20 milliseconds rather than taking an interrupt on each input
dhu(%d,%d): NXM fault. 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. It is not seri‐
dhu%d: silo overflow. 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 lines
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.
The dhu driver appeared in 4.3BSD.
4.3 Berkeley Distribution June 5, 1993 4.3 Berkeley Distribution