need to read BOOT0 pin on STM32H725

[JCase.1]

I have designed a set of boards for a client with one USB interface to the main controller.  We can bootload it by the usual methods, and bootload the CPUs on the other boards by pass-thru from the main controller.  I send coded messages to the main controller which properly toggles BOOT0 and nRESET on the downstream boards and then goes into pure passthru. 

So far, we have always toggled the BOOT0 pin to the main controller to signal when to exit pass-thru mode.  Always worked, no problem.

We have a new version using an STM32H725.   I now find that it has a dedicated BOOT0 pin.   Prior CPUs always had the BOOT0 pin mapped to a GPIO pin, so that we could read it to exit pass-thru, but I can't do that now.

I have dug around hoping to find something in a SYSCFG register to read the BOOT0 pin, but no luck.

Am I totally shot here, or is there any trick to read a dedicated BOOT0 pin that isn't mapped to GPIO?   If I can't do this, it will have to get messy (embedded escape codes in the data stream...yuk.)

Thanks in advance and happy new year!

Jeff Casey  /  Rockfield Research Inc.

[TDK]

Sorry, no way to read the current value of the BOOT0 pin. You could tie it to an unused GPIO and read it that way. I don't even see a way to determine what the value was on boot, like you can do on other chips.

The BOOT0 pin has a different internal structure than other I/O pins. Way lower leakage current, higher max input voltage. It would make sense for the designers not to allow hook up the general purpose input functionality in favor of lower power usage.