CPU_ELAN(4) | FreeBSD Kernel Interfaces Manual (i386) | CPU_ELAN(4) |
NAME
CPU_ELAN — AMD Elan 520 CPU supportSYNOPSIS
options CPU_ELANoptions 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.
HISTORY
The CPU_ELAN code first appeared in FreeBSD 4.7.AUTHORS
<phk@FreeBSD.org>November 23, 2003 | FreeBSD |