My email address is on the front page of the System Reference Manual. Gerald
On Wed, Feb 19, 2014 at 7:45 AM, v++ <[email protected]> wrote: > How do I ask the designer? > > > On Wednesday, February 19, 2014 8:43:05 AM UTC-5, Gerald wrote: > >> Did you ask the designer? >> >> Gerald >> >> >> >> On Wed, Feb 19, 2014 at 7:33 AM, <[email protected]> wrote: >> >>> I was having flaky USB behavior on multiple BBB boards and so >>> investigated the USB Power control circuitry. Her is what I found. >>> >>> The Pull-Up resistor on the USB1_OCn signal has an invalid voltage >>> reading. The pull up should set the signal at 3.3V as the resistor is >>> attached to a 3.3V supply. (this was verified through measurement). The >>> value of the pull up is 10K as shown. >>> Essentially what I see is that during certain USB activity the main >>> processor will disable the USB1_DRVVBUS signal which turns off USB power. >>> My theory is that the voltage level on the USB1_OCn signal is close to the >>> value which would indicate an Over Current condition. >>> The processor then removes power and disable the USB bus. (this is my >>> theory but I am not positive on this) >>> >>> What is a fact is that the voltage on the USB1_OCn signal is at an >>> improper logic value for a 3.3 Volt IO signal. The processor will at times >>> remove the USB1_DRVVBUS signal hence removing USB power. >>> >>> I have watched the USB1_OCn signal while the processor removes the >>> USB1_DRVVBUS signal. It does not change value to 0 volts as would be >>> expected when a true over current condition occurs. I also forced the Over >>> Current condition by grounding the USB1_OCn signal to verify that the >>> processor will remove the USB_DRVVBUS signal when a truen OC event occurs. >>> It did remove the USB_DRVVBUS signal as expected. >>> >>> To investigate why the USB1_OCn signal was being held in an improper >>> state, I lifted Pin 5 of U8 removing the open drain driver. The voltage >>> remained at the incorrect logic level showing that the culprit is not U8. >>> >>> I tried to come up with a work around by lifting pin 4 of U8 and pulling >>> it high such that the processor could not remove the power from the USB >>> port. In this case the kernal will not recognize the USB port. During >>> boot, the USB_DRVVBUS signal never goes to a high state. I monitored this >>> signal even though it was not attached to U8. I believe the USB Bus >>> voltage is present at the main processor before the main processor wanted >>> it be there and during boot gets upset and does not enable the port. >>> >>> So.... >>> >>> Can anyone from Beagle explain why the voltage on R52 is sitting at 2.4 >>> volts? >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >> >> -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/groups/opt_out. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
