Hi Scott,

I already set the timers in capture mode from userspace with:
echo 0x103 > /sys/kernel/debug/omap_mux/gpmc_ncs6

Then to check the changes I did
cat /sys/kernel/debug/omap_mux/gpmc_ncs6

Which gave me the output:

name: gpmc_ncs6.gpt11_pwm_evt (0x480020ba/0x08a = 0x0103), b p8, t NA


signals: gpmc_ncs6 | sys_ndmareq3 | mcbsp4_dx | gpt11_pwm_evt | gpio_57 | NA | NA | safe_mode

Now I want to now how to access the signal GPT8_EVENT_CAPTURE so I can get the length of a pulse very accurately.

Do you have any suggestion for this?

P.S. Markus I got it working with GPIO events using poll() but it was not enough accurate for my application. But thank you for your help.



2014-03-18 15:23 GMT-06:00 Scott Ellis <scott@jumpnowtek.com>:
I think you still have to write a custom kernel driver to use
the timers  GPT8-GPT11 in capture mode. You can mux the
timer pads out pins 27-30 on the 40 pin expansion headers.

I did it before for a customer a few years ago. It wasn't too
difficult. We could count pulses at 1 kHz pretty accurately
I can see from my notes. That's the highest frequency the
the customer was interested in. I don't know offhand the
upper limit.

If you want take a look at this pwm driver to get some rough
ideas on how to get started.


A capture driver has a different purpose, so the interface will
change. I used ioctls for everything. It's the same timers though,
just configured in PWM vs CAPTURE mode.

The reference was the TRM section 16.

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Roque Lora
Graduate Research Assistant of Electrical Engineering
AggieAir Flying Circus (http://aggieair.usu.edu/)
Utah State University
Logan, UT, USA