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.
