Speed up start up after leaving system off

[Marelcom]

Hi

We use the nRF52832 for an NFC device. The device is 99.9 %  in the system off state to save power as much as possible. because the device is power by a button cell battery. The device has an e-paper and the display data are transfered over NFC. The user has the possible the change the displayed data with a external button.

uP = nRF52832
SDK = nRF Connect v2.6.1

In two case the device must wake up.
- User pushes the button
- Device receives new Data over NFC

At the moment the device is running well. But our customer wants the have the possibility to do a DFU over BLE. After adding the follwing modules to the "prj.conf" file the start up takes about 1 second, after leaving the system off mode. This is way to long. The usere wants to have a reaction from device after around 100ms when pushing the external button.

# Enable Bluetooth for FOTA (DFU)

CONFIG_BT=y

CONFIG_BT_PERIPHERAL=y

CONFIG_BT_DEVICE_NAME="TestDevice"

# Enable MCUboot and FOTA

CONFIG_BOOTLOADER_MCUBOOT=y

CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y

Is there a way to shorten the start up time from system off mode?
Like enabling the moduls for FOTA (DFU) only when the useres wants to start the DFU mode while pushing a button and save the maximum power in deep sleep mode.

thanks and best regards
Markus

[Einar Thorsrud]

Hi Markus,

I suspect that the main contributer to the increased startup time is from the bootloader validating the application image. You can disable that using CONFIG_BOOT_VALIDATE_SLOT0=n. If you do, the image will only be validated during DFU, but not for subsequent boots. Please note that this means that if for any reason the application region is corrupted or manipulated, the bootloader will boot it non the less, which you should be aware of from a security perspective.