[gen4] prebootloader: fix STOP/ULP sleep with disabled rtos, get correct wake-up reason

[avtolstoy]

Problem

IPC communications are currently broken with KM0 after 1 STOP/ULP sleep cycle when WiFi interface is not initialized and thus KM0 RTOS and WiFi firmware are not initialized.

Solution

taskENTER_CRITICAL() and taskEXIT_CRITICAL() should only be used if RTOS has been started.

This PR also improves RTC wake-up reason detection.

Steps to Test

Run the test app below with both WiFi.on() in setup() and without it. Wake-up reason should be correct, sleep time should be correct too in both cases through multiple sleep cycles.

Example App

#include "application.h"

SerialLogHandler dbg1(LOG_LEVEL_ALL);
SYSTEM_THREAD(ENABLED);
SYSTEM_MODE(SEMI_AUTOMATIC);

void setup() {
    // IMPORTANT: Run with WiFi.on() below and without it, should work in either case correctly.
    // WiFi.on();
    delay(1000);
}

SystemSleepResult result;
system_tick_t start = 0, end = 0;

void loop() {
    waitUntil(Serial.isConnected);
    delay(1000);
    Log.info("Start sleep test slept=%u result=%d", end - start, (int)result.wakeupReason());

    SystemSleepConfiguration config;

    config.mode(SystemSleepMode::ULTRA_LOW_POWER)
        .gpio(A7, FALLING)
        .duration(30s);

    Log.info("going to ULP");
    delay(10);

    start = millis();
    result = System.sleep(config);
    end = millis();
}

References

N/A

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[XuGuohui]

Just wondering why this matters. Is it the root cause of the sleep duration being incorrect?

[avtolstoy]

In non-RTOS mode (when WiFi firmware is not initialized) this will disable interrupts and we'll no longer wake up KM0 on IPC interrupts. So 5 second 'sleep' was actually just a 5 second timeout waiting to get an IPC response.