IOASIC(4) | Device Drivers 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 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

asc(4), bba(4), intro(4), le(4), mcclock(4), tc(4), zs(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.

September 12, 2007 | NetBSD 9.3