edison.md: add some SPI limitations

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

diff --git a/docs/edison.md b/docs/edison.md
index e4cc6d0..7199373 100644 (file)
--- a/docs/edison.md
+++ b/docs/edison.md
@@ -20,6 +20,9 @@ in libmraa:
 - i2c is exposed on i2c-6, therfore you must use bus 6 and not bus 0
 - PWM avaible on default swizzler postions. (3,5,6,9)
 - SPI exposed is also used for the ADC. Try not to use your own CS.
+- Max SPI speed is 25Mhz/4 ~6.25Mhz
+- SPI PM can sometimes do weird things you can disable it with:
+  echo on > /sys/devices/pci0000\:00/0000\:00\:07.1/power/control
 - ADC kernel module will return 12bit number but the ADC itself only has an
   accuracy of 10bits. This ADC is only included on the arduino board.
 - AIO pins are treated as 0-5 in mraa_aio_init() but as 14-19 for everything