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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⟩