CPU_ELAN(4) BSD/i386 Kernel Interfaces Manual 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 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 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 sig-
nal. 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), 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
