[Gumstix-users] PWMs, GPIO output, muxing

[zachlac <zlacelle@gm...>]

I see 6 pwm's listed on the Gumstix sheet for the 40-pin Tobi header, but
only 3 seem to be active--8, 9, and 11.  10, 0, and 1 do not seem to work. 
How can I debug this, and what would cause this problem?

Also, using the /sys/class interface, I can only control GPIO output on 1
GPIO; the 1-wire serial, GPIO170.  I can also control the PWM's this way,
but none of the other GPIO's.  I'm looking at pin muxing, and it seems that
all you can control is IEN (input enable) and not output.

Basically, any help with how to actually control GPIO, and troubleshoot
these lower-level problems, is welcome.  I've looked around the forum for
quite a while, and I didn't find anything to specifically address these
issues.

-Zach
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Re: [Gumstix-users] PWMs, GPIO output, muxing

[ekoshimo <ed.t.koshimoto@na...>]

Hi Zach,

I'm learning about GPIOs myself, and I haven't gotten too far with actual
success yet.  However, I believe I'm on my way.  I've read this article at
jumpnow.com titled "Overo GPIO" which gave me a good starting point. 
Basically I've looked in my overo's /sys/class/gpio directory to see which
GPIOs are active.  Then I looked at the schematic for the expansion board
I'm using (SUMMIT) to see what the 40-pin header assignments are.  Then I
looked at the OMAP3530 Technical Reference Manual Table 7-5 to see what the
GPIO definitions and possible mux values are.

I see gumstix wiki articles on GPIO and GPIO event which seem like more
relevant information.  I'm not sure how much control there is configuring
the GPIO pins at bootup; it appears there is a way with u-boot scripts and
dev2mem, but I haven't uncovered any definite information as of yet.  I'm
also looking at what userspace functions are available - it looks like you
can write a program to perform GPIO operations.

I know this doesn't immediately answer your question, but I myself am trying
to get results as soon as possible and this appears to be the best path for
me right now.

As for my goals, I'm trying to use an Overo water with the summit expansion
board to basically acquire DAC signals from another board, performing
calculations on those DAC signals, and then outputting the results on
another serial line.

Thanks,
ed

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