| CPU_ELAN(4) | Device Drivers Manual (i386) | CPU_ELAN(4) |
CPU_ELAN — AMD
Elan 520 CPU support
options CPU_ELAN
options CPU_ELAN_PPS
options CPU_ELAN_XTAL
options CPU_SOEKRIS
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 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>
| November 23, 2003 | Debian |