Hibernation

You inherited firmware for a battery-powered sensor node that sleeps between readings to conserve power. A wakeup pin on PA0 should bring the MCU out of sleep mode so it can take a measurement and report over UART.

The previous developer set up the EXTI edge detection and the ISR, but the node never wakes up. When you force-run it with the sleep call removed, the UART works fine, so the problem is somewhere in the sleep/wakeup path.

Expected behavior: the firmware prints "READY", enters sleep (WFI), wakes on a rising edge on PA0, prints "AWAKE 1", sleeps again, wakes again, prints "AWAKE 2", and so on. For example, with one wakeup event:

READY AWAKE 1

Find and fix all the bugs so the node sleeps and wakes correctly. The node must use plain sleep, not deep sleep: the grader reads SCB SCR after the run and both SLEEPDEEP (bit 2) and SLEEPONEXIT (bit 1) must be clear.