AST(4) - Device Drivers Manual #
AST(4) - Device Drivers Manual
NAME #
ast - multiplexing serial communications interface
SYNOPSIS #
ast0 at isa? port 0x1a0 irq 5 ast1 at isa? port 0x2a0 irq 6 com* at ast?
DESCRIPTION #
The
ast
driver provides support for boards that multiplex together up to four
EIA
RS-232C
(CCITT
V.28
)
communications interfaces.
Apparently the original master of hardware using this multiplexing protocol
was AST.
Each
ast
device is the master device for up to four
com
devices.
The kernel configuration specifies these
com
devices as slave devices of the
ast
device, as shown in
SYNOPSIS.
The slave ID given for each
com
device determines which bit in the interrupt multiplexing register is
tested to find interrupts for that device.
The
port
specification for the
ast
device is used to compute the base addresses for the
com
subdevices and the port for the interrupt multiplexing register.
On a real AST card, the jumpers are as follows:
SW1-1
Turn ON for irq 2. Default is OFF.
SW1-2
Turn ON for irq 3. Default is OFF.
SW1-3
Turn ON for irq 4. Default is OFF.
SW2-1
Turn ON for irq 5. This is ON for the first card, OFF otherwise.
SW2-2
Turn ON for irq 6. This is ON for the second card, OFF otherwise.
SW2-3
Turn ON for irq 7. Default is OFF.
SW3-1
“Compatible mode”. The ast driver needs extended mode, so leave this OFF.
SW3-2
I/O Address. In extended mode, this should be OFF for the first card at 0x1a0-0x1a7 and ON for the second card at 0x2a0-0x2a7.
SW3-3
Interrupt sharing. Default is OFF.
SW3-4
Reserved, must be OFF.
FILES #
/dev/tty0?
SEE ALSO #
HISTORY #
The ast driver was written by Roland McGrath and placed into the public domain.
OpenBSD 7.5 - May 21, 2008