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 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.

SEE ALSO

       led(4), timecounters(4), sysctl(8)

HISTORY

       The CPU_ELAN code first appeared in FreeBSD 4.7.

AUTHORS

       Poul-Henning Kamp <phk@FreeBSD.org>

Debian                                          November 23, 2003                                    CPU_ELAN(4)