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