---
name: "ioasic"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/ioasic"
---

# ioasic(4)

baseboard IO control ASIC for DEC TURBOchannel systems

## 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 DEC 3000 TURBOchannel machines.

The **ioasic** provides hardware DMA channels and interrupt support for several baseboard devices, including one [asc(4)](/asc/4.md) SCSI device with a scatter/gather DMA channel, an mc146818-compatible **mcclock**, an Am7930 audio device [bba(4)](/bba/4.md), two [zs(4)](/zs/4.md) dual-port serial devices, and an AMD 7990 LANCE [le(4)](/le/4.md) Ethernet interface.

The **ioasic** is also used for the audio/ISDN hardware on 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.

## SEE ALSO

[asc(4)](/asc/4.md), [bba(4)](/bba/4.md), [intro(4)](/intro/4.md), [le(4)](/le/4.md), [zs(4)](/zs/4.md)

## HISTORY

The **ioasic** driver first appeared in NetBSD 1.1, derived from DECstation boot-time configuration code in 4.4BSD.