---
name: "CPU_ELAN"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/CPU_ELAN"
---

# CPU\_ELAN(4)

AMD Elan 520 CPU support

## NAME

**CPU\_ELAN** – AMD Elan 520 CPU support

## SYNOPSIS

**options CPU\_ELAN** **options CPU\_ELAN\_PPS** **options CPU\_ELAN\_XTAL**

-

  *machdep.elan\_gpio\_config*

-

  *machdep.elan\_freq*

**options CPU\_SOEKRIS**

## DESCRIPTION

The **options CPU\_ELAN** enables support for the AMD Elan 520 CPU.

A device */dev/elan-mmcr* exports the MMCR register bank to userland using [mmap(2)](/mmap/2.md).

The i8254 timer will be adjusted to the slightly unorthodox frequency 1189161 Hz (32768 \* 45 \* 25 / 31) employed by the Elan.

A timecounter named “ELAN” is implemented using the general purpose timer 2, but it will not be usable unless HZ is configured at 150 or higher. This timecounter is much better than the “i8254” timecounter and should be used at all times.

The *machdep.elan\_gpio\_config* [sysctl(8)](/sysctl/8.md) variable enables configuration of the GPIO pins of the CPU. The string must be exactly 32 characters long. A ‘-’ means the GPIO is unavailable. A ‘l’ (lower-case ell) configures a [led(4)](/led/4.md) device (active low). A ‘L’ configures a [led(4)](/led/4.md) device (active high). A ‘.’ means no configuration for this GPIO. These [led(4)](/led/4.md) devices will be named */dev/led/gpio%d*. For meaning of ‘P’, ‘e’ and ‘E’, see under **options CPU\_ELAN\_PPS**.

The **options CPU\_ELAN\_XTAL** and the *machdep.elan\_freq* [sysctl(8)](/sysctl/8.md) variable can be used to set the CPU clock crystal frequency in Hz. The default is 33333333 Hz.

The **options CPU\_ELAN\_PPS** enables precision timestamping using the RFC2783 PPS-API via the */dev/elan-mmcr* device. The resolution will be approximately 125 nsec and the precision ± 125 nsec. (For 125 nsec read “4 / CPU clock crystal frequency”.)

The input signal must be connected to the TMR1IN pin and a GPIO pin. The GPIO pin must be configured with a ‘P’ in *machdep.elan\_gpio\_config*.

In addition, one GPIO pin can be configured with either ‘e’ (active low) or ‘E’ (active high) to become a “echo” output of the input signal. Please notice that this signal is not suitable for calibration.

If the **options CPU\_SOEKRIS** is given, the support will additionally be tailored to the Soekris Engineering 45xx series of embedded computers. The “error” led will be configured (as */dev/led/error*) and the GPIO pins which are not available will be disabled.

## SEE ALSO

[led(4)](/led/4.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **CPU\_ELAN** code first appeared in FreeBSD 4.7.

## AUTHORS

Poul-Henning Kamp ⟨phk@FreeBSD.org⟩