---
name: "uturn"
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/uturn"
---

# uturn(4)

U2/Uturn, Runway to GSC Bus bridge & IOA

## NAME

**uturn** – U2/Uturn, Runway to GSC Bus bridge & IOA

## SYNOPSIS

**uturn\* at mainbus?** **astro\* at uturn?** **dino\* at uturn?** **lasi\* at uturn?** **gecko\* at uturn?** **sti\* at uturn?**

## DESCRIPTION

**uturn** provides the functionality of IOA (not currently supported) as a bridge from the Runway bus (see [runway(4)](/runway/4.md) for more information) to GSC. Modern systems, based on the PA-8000 and later 64-bit CPUs, use the **U-Turn** version, whilst earlier systems, based on the PA-7200 CPU, used a different version of the chip called **U2**.

## SEE ALSO

[astro(4)](/astro/4.md), [cpu(4)](/cpu/4.md), [dino(4)](/dino/4.md), [gecko(4)](/gecko/4.md), [gsc(4)](/gsc/4.md), [intro(4)](/intro/4.md), [pci(4)](/pci/4.md), [runway(4)](/runway/4.md), [sti(4)](/sti/4.md)

## HISTORY

The **uturn** driver appeared in OpenBSD 3.7.