NAME
ioasic —
baseboard IO control ASIC for
DEC TURBOchannel systems
SYNOPSIS
ioasic0 at tc? slot ? offset ?
DESCRIPTION
The
ioasic driver provides support for the DEC proprietary
IOCTL ASIC found on all DEC TURBOchannel machines with MIPS (DECstation 5000
series, excluding the 5000/200) and Alpha (3000-series) processors. On these
machines (including the 5000/200), all baseboard devices should be configured
as children of the
ioasic device.
The
ioasic provides hardware DMA channels and interrupt
support for several baseboard devices, including one
asc
SCSI device with a scatter/gather DMA channel, an mc146818-compatible
mcclock, an Am7930 audio device
bba, one
or two
zs two-port serial devices, and a AMD 7990 LANCE
le Ethernet interface.
The
ioasic is also used for the floppy-disc drive and
audio/ISDN hardware on the Personal DECstation and audio-equipped TURBOchannel
Alphas, where the
ioasic hardware provides a scatter-gather
DMA channel between the 16-bit device and the 32-bit
tc DMA
address space.
Support for scatter-gather DMA eliminates the need for additional copying. A
baseboard
asc SCSI adaptor attached to an
ioasic will give slightly better performance than its
tc counterpart.
SEE ALSO
asc(4),
bba(4),
intro(4),
le(4),
mcclock(4),
tc(4),
zs(4)
HISTORY
The
ioasic driver first appeared in
NetBSD
1.1, derived from DECstation boot-time configuration code in
4.4BSD.
BUGS
The DECstation 5000/200 does not actually have an IOASIC chip, but for
consistency it must be configured as if it did.