DH(4)

NAME
dh - DH-11/DM-11 serial multiplexer device interface

SYNOPSIS
dh0 at uba0 csr 0160020 vector dhrint dhxint [flags]
dm0 at uba0 csr 0170500 vector dmintr [flags]

DESCRIPTION
NOTE: This driver has not been ported from 4.4BSD yet.

A DH-11 provides 16 serial communication lines; DM-11s may optionally be paired with DH-11s to provide modem control for the lines.

An optional argument flags may be supplied with the device specification in the config(1) file indicating that the line corresponding to bit number i is not properly connected, and should be treated as hard-wired with carrier always present. Thus specifying ‘flags 0x0004’ for dh0 would cause line ttyh2 to be treated in this way.

Normal I/O control parameters for individual lines are managed by ioctl(2) calls. Line speeds may be initiated via getty(8) and stty(1) or may be communicated by other programs which use ioctl(2) such as ifconfig(8), see tty(4).

The dh driver monitors the rate of input on each board, and switches between the use of character-at-a-time interrupts and input silos. While the silo is enabled during periods of high-speed input, the driver polls for input 30 times per second.

FILES
/dev/tty[h-o][0-9a-f]
/dev/ttyd[0-9a-f]

DIAGNOSTICS

dh%d: NXM. 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 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. It is not serious.

SEE ALSO
tty(4)

HISTORY
A dh driver appeared in AT&T UNIX.