Provided by: freebsd-manpages_8.2-1_all
CPU_ELAN -- AMD Elan 520 CPU support
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
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) 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) device (active low). A 'L' configures a led(4) device (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
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.
The CPU_ELAN code first appeared in FreeBSD 4.7.
Poul-Henning Kamp <phk@FreeBSD.org>