On Wednesday, 29 April 2015 17:30:14 UTC+2, Matthijs van Duin wrote: > > Your original question is actually very easy to answer >
I posted a bit too hastily since I missed the second half of your original post. If external hardware unconditionally drives or pulls up to 3V3EXP (in case of BBW) or 3V3B (in case of BBB) then at shutdown they are indeed applying power to IOs while the corresponding power domain has already been shut down, which is not allowed. The BBB SRM (but not the BBW SRM) warns that "no pins are to be driven until after the sys_reset line goes high" but this statement isn't quite right since it only addresses boot and not shutdown (it should say "unless the sys_reset line is high") and pull-ups can also cause problems. Powering processor IO banks and attached hardware using separate supply lines is tricky to get right, all versions of beaglebones get it wrong, and it was wrong to dump responsibility for these issues onto CAPE developers by putting a statement like that in the SRM. The mandate given in the SRM is actually also violated by on-board peripherals of the BBB, for example by the UART level shifter. I think the best solution would have been to have the regulator controlled by the PMIC_PGOOD output which also controls the power-on-reset input of the AM335x, but this too would need to be carefully analyzed to verify it doesn't cause issues. -- 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.
