cpu_elan(4)

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).

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 gener

al 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) variable enables con

figuration 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) device (active low). A `L' configures a led(4) de

vice (active
high). A `.' means no configuration for this GPIO. These

led(4) 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) 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 us

ing 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 in

put signal.
Please notice that this signal is not suitable for calibra

tion.

If the options CPU_SOEKRIS is given, the support will addi

tionally 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), sysctl(8)

HISTORY

The CPU_ELAN code first appeared in FreeBSD 4.7.

AUTHORS

Poul-Henning Kamp <phk@FreeBSD.org>

BSD November 23, 2003

BSD