ASB Code Execution w/ Arduino Serial Monitor Left Open

[oclyke]

Subject of the issue

Code uploaded using the ASB (Ambiq Secure Bootloader) does not execute if the Arduino Serial Monitor was left open (not "connected," but just "visible and greyed out") during upload. It won't even begin after a manual reset is applied to the board

Your workbench

• RedBoard Artemis ATP
• Arduino 1.8.12
• Bootloader: Ambiq Secure Bootloader

Steps to reproduce

• Upload any sketch w/ the monitor closed
• Observe working sketch (say, Blink)
• Open the Arduino serial monitor
• Upload the same sketch again w/o any modification (leaving monitor open)
• Arduino will grey out the monitor, thus allowing the ASB to connect on that port
• The upload will complete successfully
• The code will not execute....
• Resetting the board will not start program execution...

Expected behaviour

The state of the serial monitor should not affect firmware uploads (port conflicts disregarded)

Actual behaviour

See "Steps to reproduce"