IOASIC(4)             OpenBSD Programmer's Manual (PMAX)             IOASIC(4)

NAME
     ioasic - baseboard IO control ASIC for DEC TurboChannel systems

SYNOPSIS
     ioasic0 at tc?

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 ma-
     chines (including the 5000/200), all baseboard devices should be config-
     ured as children of the ioasic. 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, one or two scc two-port serial devices, and a am9770 LANCE le
     Ethernet interface.

     The ioasic is also used for those floppy-disc drive and audio/ISDN hard-
     ware on the Personal DECstation and audio-equipted TC Alphas, where the
     ioasic hardware provides a scatter-gather DMA channel between he 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), 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.


OpenBSD 2.9                     August 6, 1996                               1
