From: Lee Azzarello <lee@ro...> - 2007-12-02 01:59:34
I have an original audiostix and a connex 400. I'm running buildroot
1161 due to the 4 megs of flash on this board. I need to detect a
voltage change from a switch which will act as a low RPM (400-1000)
tachometer. It's really just a hacked bicycle speed sensor. After
reading about GPIO lines I decided this was the right way to get some
voltage changes into the gumstix. The audiostix has 10 exposed GPIO
pins. I touched a multimeter to the pins and found that some output
3.3v and other output 0v. I tried to read the UCB1400 documentation
to figure out how the pins correspond to the devices in /proc/gpio
but I could not find a translation table.
Then I found the gpio-event driver. I loaded the binary built for my
kernel and enabled monitoring on GPIO devices 0-9 in /proc/gpio. The
logic being that since there's no documentation of how the devices in
userland correspond to the pins on the audiostix, maybe it's a
I'm monitor the first pin and use the 7th as the ground (as
documented). The multimeter reads 3.3v. The moment that I run the
gpio-event monitoring program, the multimeter drops to 0v. Now I
cannot get it to output 3.3v again regardless of reboots.
It appears that I broke something and I'm not sure what. I can't get
the voltages from these pins back to their original state. How would
I get pin 1 once again to output 3.3v to my sensor and detect when it
drops to 0v as the switch opens?
I have concluded I don't know how GPIO works but I haven't found any
information on the mailing list or wiki about this subject beyond
changing GPIO settings via /proc and running gpio-event. Both of
which have done little for me except leave the system in an unknown
Thanks for your help,
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