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@(#)dhu.4 6.1 (Berkeley) 07/25/85

C 6 dhu - DHU-11 communications multiplexer "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 behaves as described in tty (4). 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); see tty (4) for the encoding.

Bit i 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 ttyh2 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.

/dev/tty[hi][0-9a-f] tty(4) 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 rk07's) are present. It is not serious.

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 for example.

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.