NAME
ioasic —
baseboard IO control ASIC for DEC
TURBOchannel systems
SYNOPSIS
ioasic0 at tc? slot ? offset ?
DESCRIPTION
Theioasic 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
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.