nrf_fstorage_write takes long time to write

[min-ching]

Hi,

    I did some benchmark on internal flash access and found it takes more than 2 seconds for the device to write 16kB data. I timed by "nrf_fstorage_is_busy". Is this normal to have such long time to write 16kB(0x4000)? Is there better way to write a big chunk of data at once? 

Thank you,

Min-Ching

[Håkon Alseth]

Hi,

 

Continuous 16k write to flash would take approx. 165 ms on nRF52840 (typ. 41 us per word), and up to 1.4 sec on nRF52832 (67.5 us to 338 us per word)

Are you using the SoftDevice? What would happen then is that the flash operation(s) will be queued in between softdevice events, so the overall time for performing the operation would depend on any other activity.

If you checkout the two different ways of storing to flash in nrf_fstorage_nvmc.c::write() and nrf_fstorage_sd.c::write(), you can see how the two are handled differently.

 

Cheers,

Håkon

[min-ching]

Hi Håkon,

     I'm using SoftDevice. I don't expect to see a 165ms operation became 2000ms. Did I do something wrong? We do have a HRS code running along with to do the benchmark. Is it possible to tweak this?

Thank you,

Min-Ching

[Håkon Alseth]

Hi Min-Ching,

 

When running with the SoftDevice, it is expected that flash operations take longer time, as the application only queues the flash-operation, and it is executed by the SoftDevice in between your connection intervals. This is explained more in detail here:

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.sds/dita/softdevices/s130/multilink_scheduling/flash_api_timing.html?cp=2_3_1_0_14_7

You could try writing in smaller chunks, or do the flash operation when the softdevice is disabled (ie: use direct access to the NVMC peripheral)

Best regards,

Håkon