dh(4) Unsupported dh(4)Namedh - DH-11/DM-11 communications multiplexer
device dh0 at uba? csr 0160020 flags 0x???? vector dhrint dhxint
device dm0 at uba? csr 0170500 flags 0x???? vector dmintr
A DH-11 provides 16 communication lines; DM-11's may be optionally
paired with DH-11's to provide modem control for the lines.
Each line attached to the DH-11 communications multiplexer behaves as
described in Input and output for each line may independently be set to
run at any of 16 speeds; see for the encoding.
Bit i of flags may be specified for a to say that a line is not prop‐
erly connected, and that the line should be treated as hard-wired with
carrier always present. Thus specifying ``flags 0x0004'' in the speci‐
fication of dh0 would cause line ttyh2 to be treated in this way.
The driver normally uses input silos and polls for input at each clock
tick (10 milliseconds) rather than taking an interrupt on each input
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 rk07's) are present. It is not serious.
dh%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 will then print a message on the console with
interrupts disabled. If the Berknet is running on a line at high speed
(for example, 9600 baud), there is only 1/15th of a second of buffering
capacity in the silo, and overrun is possible. This may cause a few
input characters to be lost to users and a network packet is likely to
be corrupted, but the network will recover. It is not serious.