PocketBeagle… power supply dimensioning and power-off detection

Hi all,

I'm slowly getting a small board together using the PocketBeagle for
logic analysis and stimulus.

For now, my experiments have revolved around powering the device off a
USB host, however I'd like to eventually have the board self-powered via
a 4-cell lithium battery pack, stepping that down to +5V for Vin.

To power USB VBus, I have a Maxim MAX1607 wired up. Currently, I have
hooked its nEN pin to 0V, since as far as I know, the V_EN pin on the
PocketBeagle is active-high, and my USB chip requires active-low.

This is hooked up according to the diagram at

with one difference, since I initially followed the advice on the FAQ, I
have USB1 V_Bus (pin 5) and USB1 V_In (pin 7) bridged.

This worked, but I still get some issues with the USB dropping out
momentarily, which can be seen on the console.

shows the messages that can be seen on the console.

I suspect that moving to an external 5V DC supply on the Vin pin of the
PocketBeagle will improve this.

I don't expect to be driving anything high-current off the GPIO pins, as
I know they won't handle it. LEDs would be about as high as I'd expect.

Based on this, what current capacity do people recommend for these? I
have a stack of Rohm BP5293-50s which are 3-pin switchmode devices good
for 500mA: http://www.rohm.com/web/global/products/-/product/BP5293-50

Is 500mA sufficient, or should I aim higher? Other recommendations?

The other problem I have is knowing when to kill the power. Is there a
pin I can monitor on the PocketBeagle's GPIOs that could tell me when
the device has halted? I could configure a GPIO as a "LED" and set it
to heartbeat, but that's a messy way to find out if something is down.

If there was a pin that went high, or low, when the CPU halted, that'd
be ideal, as then I could use that to kill the power.