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.Dd September 12, 2007
.Dt IOASIC 4
.Os
.Sh NAME
.Nm ioasic
.Nd
baseboard IO control ASIC for DEC TURBOchannel systems
.Sh SYNOPSIS
.Cd "ioasic0 at tc? slot ? offset ?"
.Sh DESCRIPTION
The
.Nm
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
.Nm
device.
.Pp
The
.Nm
provides hardware DMA channels and interrupt support for several
baseboard devices, including one
.Nm asc
SCSI device with a scatter/gather DMA channel, an mc146818-compatible
.Nm mcclock ,
an Am7930 audio device
.Nm bba ,
one or two
.Nm zs
two-port serial devices, and a AMD 7990 LANCE
.Nm le
Ethernet interface.
.Pp
The
.Nm
is also used for the floppy-disc drive and audio/ISDN hardware on
the Personal DECstation and audio-equipped TURBOchannel Alphas,
where the
.Nm
hardware provides a scatter-gather DMA channel between the 16-bit
device and the 32-bit
.Nm tc
DMA address space.
.Pp
Support for scatter-gather DMA eliminates the need for additional copying.
A baseboard
.Nm asc
SCSI adaptor attached to an
.Nm ioasic
will give slightly better performance than its
.Nm tc
counterpart.
.Sh SEE ALSO
.Xr asc 4 ,
.Xr bba 4 ,
.Xr intro 4 ,
.Xr le 4 ,
.Xr mcclock 4 ,
.Xr tc 4 ,
.Xr zs 4
.Sh HISTORY
The
.Nm
driver
first appeared in
.Nx 1.1 ,
derived from DECstation boot-time configuration code in
.Bx 4.4  .
.Sh BUGS
The DECstation 5000/200 does not actually have an IOASIC
chip, but for consistency it must be configured as if it did.