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SoftDevice preventing low-power state

I'm working on a BLE design for nRF52832, with SoftDevice S132 v5.0.0. The project uses FreeRTOS with Tickless Idle enabled. When the user powers the device off (from a UI perspective, not actually cutting power to the uP) there should be almost nothing happening and the device should go into System-on low-power for an extended period of time (seconds, if not longer). What I'm seeing, however, is that FreeRTOS calls sd_app_evt_wait() but that function returns very quickly (within about 5us) and there is no power saving.

When entering the device-off state, we call sd_ble_gap_disconnect(), ble_advertising_start(&m_advertising, BLE_ADV_MODE_IDLE), and sd_ble_gap_adv_stop() which I think should be enough to ensure the SoftDevice is completely idle.

If I *also* call nrf_sdh_disable_request() to disable the SoftDevice, then FreeRTOS calls __WFE() and the device sees significant power savings.

I would really prefer not to have to disable the SoftDevice in order to achieve useful power savings. Is there something I can do to figure out why it's not actually sleeping when I think it should be?

Thanks,
--Russ

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  • In most SDK examples, the call to nrf_pwr_mgmt_run() inside the main for or while loop calls the sd_app_evt_wait() function & then afterwards calls the _WFE() function, which puts the CPU into a low power state. Take a look at the blinky central example inside the sdk/ble_central folder for example. You should not have to disable the softdevice in order to get power savings.

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  • In most SDK examples, the call to nrf_pwr_mgmt_run() inside the main for or while loop calls the sd_app_evt_wait() function & then afterwards calls the _WFE() function, which puts the CPU into a low power state. Take a look at the blinky central example inside the sdk/ble_central folder for example. You should not have to disable the softdevice in order to get power savings.

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