BBB Not booting with with P8.43, P8.45, P8.46 connected to a device

Hi guys,
I need to use P8.43, P8,45 and P8.46 pins, and my circuit - in true is an ESC to control motors, connected to this pins, beagle is not booting - the leds are always off. Without anything connected the beagle boots.
There is a way do disable this behavior ?


These pins are INPUT by default… sounds to me like you, at some point, change the mode to either PWM or PRU EGP or some other OUTPUT mode.

debian@bbb42:~$ config-pin -q P8-43
P8_43 Mode: default Direction: in Value: 0
debian@bbb42:~$ config-pin -q P8-45
P8_45 Mode: default Direction: in Value: 0
debian@bbb42:~$ config-pin -q P8-46
P8_46 Mode: default Direction: in Value: 0

the board may be detects (somehow) that there is a voltage on an INPUT pin before the board (PMIC) is ready, and rather than trash the board, refuses to boot.

since you haven’t provided any detail on your ESC, the best I can do is speculate, just sayin



Hi @gomer

in true, the leds - user leds even turn on - the esc is a regular esc and I believe - read somewhere once there are signals/voltage in certain pins, the BBB/uboot look for boot in other places than sd/mmc - modify the device tree I don’t believe will solve this once because is something related to uboot or something like that. If i remove the esc from the pins and turn on the beagle and after the leds turn on I connect the esc, everything work fine.

Those pins are read by the chip when it powers up. Check the schematic for the BBB, page 6. You will see that they have either pull ups or pull downs of 100k to set the boot mode.

P8-43  - lcd-data2 - pulled high
P8-45  - lcd-data0 - pulled down
P8-46  - lcd-data1 - pulled high

If the ESC you are fitting has a stronger pull up/down then you are going to change the boot mode. Nothing you can do in software, this happens before anything runs. You have 2 choices, use a different pin/pins for whatever is causing the problem, or remove the offending pull up/down resistor on the ESC.

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hi @benedict.hewson