STM32L0 Freeze on setting NVIC/GPIO - arm

Question

I'm working with an STM32L073RZ CPU running MbedOS 5.11.2. Eventually I aim to get this working in a very low-power mode (STOP mode) that will be awoken with either an RTC interrupt or an interrupt from a peripheral device on pin PA_0 (WAKEUP_PIN_1). At the moment I am simply attempting to setup PA_0 as an interrupt using the STM32 HAL API. Please see my code below:
#include "mbed.h"
#define LOG(...) pc.printf(__VA_ARGS__); pc.printf("\r\n");
DigitalOut led(LED1);
Serial pc(USBTX, USBRX);
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) {
led = !led;
}
int main()
{
pc.baud(9600);
led = 1;
// GPIO SETUP
LOG("Enabling GPIO port A clock");
__HAL_RCC_GPIOA_CLK_ENABLE();
GPIO_InitTypeDef GPIO_InitStruct;
GPIO_InitStruct.Pin = GPIO_PIN_0;
GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING;
GPIO_InitStruct.Pull = GPIO_NOPULL;
LOG("Initialising PA_0");
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
// NVIC SETUP
LOG("Setting IRQ Priority");
HAL_NVIC_SetPriority(EXTI0_1_IRQn, 0, 1); // Priorities can be 0, 1, 2, 3 with lowest being highest prio
LOG("Enabling IRQ");
HAL_NVIC_EnableIRQ(EXTI0_1_IRQn);
LOG("Going into STOP mode");
HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFE);
}
As you can see, the code is broken into two sections: GPIO setup and NVIC setup. My issue is as follows:
If I perform GPIO setup before NVIC setup then the program seems to hang on HAL_NVIC_SetPriority(), however, if I perform NVIC setup before GPIO setup then the code seems to hang on HAL_NVIC_EnableIRQ().
I am completely stumped as to what is causing this. Any insight is greatly appreciated.

Answer 1

You don't need to do this manually. As long as you run Mbed OS in tickless mode (set MBED_TICKLESS=1 macro in your mbed_app.json) the MCU will automatically enter stop mode whenever all threads are idle. If you want to wake up you can either use an InterruptIn on the pin or use a LowPowerTicker.
If you're looking for the absolute lowest power modes, you can use the standby feature (without RAM retention) for which there's a library here: stm32-standby-rtc-wakeup.