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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