I need to access the SYNC_IN pin of the AD9364 embedded on a FMCOMMS4, with ZedBoard as carrier. I'm using the latest ADI Linux image (boot_2016_r2_2017_06_29).
According to the user manual, SYNC_IN is connected to the H23 pin of the FMC connector. Yet I found in the constraints file that H23 is named gpio_sync. Then gpio_sync is routed to GPIO 45 as far as I understand the system_top.
Going on Linux, in /sys/class/gpio, I found gpiochip906 which indicates that the GPIO offset is 906.
906 + 45 = 951, then:
echo 951 > export
echo high > direction
But nothing is written to the pin.
I also tried with 906 + 45 + 54 = 1005, but export fails (Device or resource busy).
It seems that other users had the same issue, but I couldn't find a way to solve it.