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IOASIC(4)		 BSD Kernel Interfaces Manual		     IOASIC(4)

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 con‐
     figured as children of the ioasic device.

     The ioasic provides hardware DMA channels and interrupt support for sev‐
     eral baseboard devices, including one asc SCSI device with a scat‐
     ter/gather DMA channel, an mc146818-compatible mcclock, an Am7930 audio
     device bba, one or two scc 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 copy‐
     ing.  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), scc(4), tc(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.

BSD			      September 12, 1996			   BSD

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