Hi Rick the "noise issue on the USB OTG" in our case appears to be due to USB OTG device probing. We see the VBUS (+5V) line pulsing high for a short period once every 2 seconds or so.When a USB controller is set to OTG and it doesn't see 5V on its VBUS input (ie no host computer is connected) then as far as I am aware, it then powers the VBUS (+5V) line on once every 2 seconds so that it can power a peripheral; USB device to see if any are present. On the Beaglebone design (and our design) the USB's VBUS line is connected to the TPS65217's USB power in line. However the USB's VBUS is connected to the AM335x's USB0_VBUS line which should only be an input (it has the USB0_DRVVBUS which should be used to enable 5V power). So why the USB0_VBUS is pulsing I do not know (AM335x bug or is the Linux kernel commanding the TPS65217 to connect the USB input to SYS_5V ?).
So ideally you shoud set the USB controller to be fixed to peripheral mode instead of OTG mode rather than short this line. Another option might be to increase the value of the resistor connected in series with the USB0_VBUS CPU line if somehow the CPU is driving this line. I would have thought that the TPS65217 should prioritise AC input rather than USB, but the datasheet does not seem to mention this so maybe it just switches to the one that has a power up edge (TPS65217 issue ?) ? However when we have set the USB controller to peripheral mode it still pulses the VBUS line. Removing the USB drivers completely eliminates the issue. RobertCNelson thanks for the info, but we already have "dr_mode" set to "peripheral" in the systems DTB file. When the system first powers up there is no USB OTG probing (oscilloscope connected) but once we load the g_ether USB gadget driver the USB0 port begins OTG probing so I suspect some kernel issue in at least 3.12.10 as well as some AM335x issue. Will carry on digging into the kernel sources and try a very recent kernel. -- 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/d/optout.
