---
name: "schsio"
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/schsio"
---

# schsio(4)

SMSC SCH311x LPC Super I/O

## NAME

**schsio** – SMSC SCH311x LPC Super I/O

## SYNOPSIS

**schsio\* at isa? port 0x2e   flags 0x0000** **schsio\* at isa? port 0x4e   flags 0x0000** **schsio\* at isa? port 0x162e flags 0x0000** **schsio\* at isa? port 0x164e flags 0x0000**

## DESCRIPTION

The **schsio** driver provides support for the SMSC SCH3112, SCH3114, and SCH3116 ICs. Among other things, the devices contain environment sensors, a watchdog timer, and fan control. The **schsio** driver supports the environment sensors and the watchdog timer.

The hardware provides the following sensors:

| | | |
| --- | --- | --- |
| **Sensor** | **Units** | **Typical use** |
| Internal diode | uK | IC internal thermal diode |
| Remote diode 1 | uK | External thermal diode |
| Remove diode 2 | uK | External thermal diode |
| FAN1 | RPM | Fan tachometer |
| FAN2 | RPM | Fan tachometer |
| FAN3 | RPM | Fan tachometer |
| +2.5V | uV | Voltage |
| +1.5V (Vccp) | uV | Voltage |
| +3.3V (VCC) | uV | Voltage |
| +5V | uV | Voltage |
| +12V | uV | Voltage |
| +3.3V (VTR) | uV | Voltage |
| +3V (Vbat) | uV | Voltage |

**schsio** provides the standard [watchdog(4)](/watchdog/4.md) interface and may be used with [watchdogd(8)](/watchdogd/8.md). The watchdog timer may be configured to a value from 1 second to 255 minutes. The watchdog timer has a resolution of 1 second in the timeout interval 1 to 255 seconds. Outside this interval, the resolution is 1 minute.

Note that the pin used for signalling the timer expiration is configurable and may on some boards be intended for other uses than this. Because of this, the chip may not by default be configured to use the pin for watchdog operation. To force the **schsio** device to use the pin for watchdog operation, the driver may be configured with an autoconf(9) *flags* setting of 0x0001.

## SEE ALSO

[intro(4)](/intro/4.md), [isa(4)](/isa/4.md), [watchdog(4)](/watchdog/4.md), [sensorsd(8)](/sensorsd/8.md), [sysctl(8)](/sysctl/8.md), [watchdogd(8)](/watchdogd/8.md), autoconf(9)

## HISTORY

The **schsio** driver first appeared in OpenBSD 4.5.

## AUTHORS

The **schsio** driver was written by Michael Knudsen ⟨*mk@openbsd.org*⟩.