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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), sysctl(8)

HISTORY

     The CPU_ELAN code first appeared in FreeBSD 4.7.

AUTHORS

     Poul-Henning Kamp <phk@FreeBSD.org>