From: Frank A. <ft...@ya...> - 2013-04-11 23:56:24
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On 4/11/2013 3:15 PM, Michael Lindemuth wrote: > Have an Overo Fire FE running the following kernel built with Yocto: > Linux <hostname> 3.5.0 #1 PREEMPT Tue Dec 18 02:25:50 EST 2012 armv7l > GNU/Linux > > For some reason the ADC channel 3 is returning a strange value: > # cat /sys/class/hwmon/hwmon0/device/in3_input > 26 > > This is supposed to be the mV value read on pin 3 of ADC. We have checked > the value of the Tobi headers for this channel and it is around 2000 mV. > Any ideas on why we are reading such a low value? > > Let me know if you need any more information to help diagnose this issue. Do you have anything connected to the USB otg port when you read the ADC? If no, then plug something into that port and then re-read your ADC. If you now get the expected value, then your problem is as follows: If nothing is connected to the USB OTG port, the phy suspension code is called. In the chain of calls that follows, the vusb3v1 regulator is disabled. However, according to the OMAP power management manual, vusb3v1 is used "to bias the analog multiplexers on the four MCPC pins between the carkit and the MADC". I've seen if there is no bias on this mux, the MADC driver returns incorrect counts on these 4 pins that should be in A/D mode. If I plug something into the USB OTG port, the MADC driver returns the expected counts. I also created a debug version of the twl4030-usb driver, with the disabling of the vusb3v1 commented out and the MADC returns the correct counts regardless of the state of the USB OTG port. Since the vusb3v1 regulator is required for the proper operation of the mux and by extension the MADC and carkit mode, I believe that the vusb3v1 regulator should never be disabled. frank agius > > Thank You! > Michael > > > > -- > View this message in context: http://gumstix.8.x6.nabble.com/twl4030-madc-read-errors-tp4967139.html > Sent from the Gumstix mailing list archive at Nabble.com. > > ------------------------------------------------------------------------------ > Precog is a next-generation analytics platform capable of advanced > analytics on semi-structured data. The platform includes APIs for building > apps and a phenomenal toolset for data science. Developers can use > our toolset for easy data analysis & visualization. Get a free account! > http://www2.precog.com/precogplatform/slashdotnewsletter > |