BLE cannot restart advertising when it is asleep.

[XuGuohui]

Problem

BLE cannot restart advertising when disconnected by peer device if sleep mode is enabled

Steps to Test

1. Build and flash the below example application.
2. Connect to device using mobile App, e.g. LightBlue.
3. Disconnect from device using mobile App.
4. Device should restart advertising automatically.

Example App

#include "Particle.h"

SYSTEM_MODE(MANUAL);

void setup() {
    BLE.advertise();
}

void loop() {
    delay(1000);
    System.sleep(SystemSleepConfiguration().mode(SystemSleepMode::STOP).gpio(D0, RISING).ble());
}

---

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)

[avtolstoy]

I assume this is here only for going through this function more easily with a debugger. Let's remove it.

[avtolstoy]

Let's reword this, I had to read it multiple times and ask additional questions to understand how this works:

Wake-up on BLE events relies mainly on SD_EVT_IRQn interrupt, which will be disabled through NVIC (not masked) when entering sd_nvic_critical_region_enter(). Normally on BLE activity we would be woken up by other high-priority SoftDevice interrupts (e.g. timers, radio events etc), however SD_EVT_IRQn would be set as pending only after we unmask high-priority SoftDevice interrupts (__enable_irq()) and after the appropriate SoftDevice interrupt handlers finish executing. We would then immediately go back to sleep and wouldn't notice this change in SD_EVT_IRQn state. As a workaround, for the duration of the sleep, we'll be bumping the priority of SD_EVT_IRQn, so that it can wake us up from stop mode (WFI) as well.

[avtolstoy]

Alternatively, I think it might be viable to simply move pending IRQ checks under __enable_irq().