In S110 SoftDevice, NRF_POWER->SYSTEMOFF is written. Why?

[Yokoyama, Atsushi]

Hello.

I'm now writing a software based on nrf51_sdk_v6_1_0/nrf51822/Board/nrf6310/s110/ble_app_hrs. The SoftDevice I'm using is s110_nrf51822_7.1.0_softdevice.hex. Why I use the version is that the target device is IC revision 2. Exactly speaking, it is nRF51822 QFAAG20 (0x0057).

When I run the code, it is working for a while (just advertising without connection). However after a few minutes later, the software crashes by HardFault. When I checked the stack area, I noticed that the RAM Block 0 and 1 looked all filled with zero. I suspected that NRF_POWER->RAMON had a wrong value but it was 0x00000003. It looked fine. However, I also noticed that the memory area would be preserved when I reset the target. Finally I noticed that writing 1 to NRF_POWER->SYSTEMOFF caused a similar phenomenon.

So I had a watchpoint on the NRF_POWER->SYSTEMOFF (0x40000500) and reran the code. By the watchpoint, I found that a code in the SoftDevice was writing 1 to the SYSTEMOFF register. It is the following code.

0x00011328: ldr r1, [pc, #424]  ; 0x114d4
0x0001132a: movs r0, #1
0x0001132c: str r0, [r1, #0]

I also confirmed that the code was called in the IRQ #11 context (RTC0_IRQ).

I guess that there is an intention that SoftDevice triggers the SYSTEMOFF, but I don't imagine the reason.

FYI, I suspected that heap or stack area was flooded but it looked okay.

Could you please let me know when and why SoftDevice triggers the SYSTEMOFF? (Do we still have a way to access RAM even though SYSTEMOFF == 1?)

Best Regards,

Atsushi

[Ulrich Myhre]

The SYSTEMOFF will be triggered at that point in the SoftDevice if you call sd_power_system_off(). This happens at line 709 in the app you are using, in the on_ble_evt handler:

case BLE_GAP_EVT_TIMEOUT:
        if (p_ble_evt->evt.gap_evt.params.timeout.src == BLE_GAP_TIMEOUT_SRC_ADVERTISEMENT)
        {
            nrf_gpio_pin_clear(ADVERTISING_LED_PIN_NO);

            // Go to system-off mode (this function will not return; wakeup will cause a reset).
            err_code = sd_power_system_off();
            APP_ERROR_CHECK(err_code);
        }
        break;

Is this what you are seeing? The purpose for this example is to enable advertisements for some time after startup, then shut down and wait for a keypress if no connection is established within the time limits.

[Yokoyama, Atsushi]

Hi Ulrich,

Thank you for the prompt answer! I'm afraid I didn't notice the code and the comment. I was reading the "S110 nRF51822 SoftDevice Specification" document only... I should have gone through the code entirely prior to panic. (I didn't image that CPU would restart by any reason if it once went to the HardFault. I'm new to ARM Cortex-M.)

I will try the keypress tomorrow as you pointed out.

Thanks and Best Regards,

Atsushi