.\"
.\" Copyright (c) 1996, 1997 Jonathan Stone.
.\" All rights reserved.
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.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"      This product includes software developed by Jonathan Stone.
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.\"    derived from this software without specific prior written permission
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.\"	$NetBSD: ioasic.4,v 1.4 1997/10/31 02:26:09 jonathan Exp $
.\"	$OpenBSD: ioasic.4,v 1.6 1999/07/09 13:35:40 aaron Exp $
.\"
.Dd August 6, 1996
.Dt IOASIC 4 pmax
.Os
.Sh NAME
.Nm ioasic
.Nd
baseboard IO control ASIC for DEC TurboChannel systems
.Sh SYNOPSIS
.Cd "ioasic0 at tc?"
.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 ioasic .
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,
one or two
.Nm scc
two-port serial devices, and a am9770 LANCE
.Nm le
Ethernet interface.
.Pp
The
.Nm
is also used for those
floppy-disc drive and audio/ISDN hardware
on the Personal DECstation and audio-equipted TC Alphas, where the
.Nm
hardware provides a
scatter-gather DMA channel between he 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 intro 4 ,
.Xr le 4 ,
.Xr mcclock 4 ,
.Xr scc 4 ,
.Xr tc 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
.Nm ioasic
chip, but for consistency it must be configured as if it
did.