Problem with example fpu_fft sdk13 nRF52832

[stefano.luna]

Hi, i'm using keil and i would like to run the fpu_fft example to perform a fft. The example works if I set 128 or 256 as number of input vector data as you can see in the picture below.

The example doesn't work with 512 or more, since I can't display the spectrum from the terminal.(picture below).

The code should work until a number of input vector element of 8192 in order to perform a 4096 bins fft

Any suggestion about this problem?

Thank you.

[bjorn-spockeli]

Hi Stephano, I am able to reproduce the behavior and I have asked the developer that made the example look into the issue. I will update my answer as soon as I hear back from him.

[bjorn-spockeli]

It is log issue. Our UARTE can send only 255 bytes of data. UART API is prepared to handle at most 256B (see nrf_drv_uart_tx). Log subsystem can handle more data, but there is lack of some assertion on uart backend (see serial_tx function in nrf_log_backend_serial, mixing uint32_t with uint8_t in nrf_drv_uart_tx).

The best solution to deal with huge amount of data on log output is use RTT to receive. You'll have to switch the NRF_LOG backend from UART to RTT, this is done by change the following values values in sdk_config:

NRF_LOG_BACKEND_SERIAL_USES_UART 0

NRF_LOG_BACKEND_SERIAL_USES_RTT 1

NRF_LOG_BACKEND_MAX_STRING_LENGTH 2048(or more if You want to draw more)

NRF_LOG_BACKEND_RTT_OUTPUT_BUFFER_SIZE 2048(or more if You want to draw more)

SEGGER_RTT_CONFIG_DEFAULT_MODE 2

And of course switch to RTT Viewer, which should automatically find RTT buffers.

[stefano.luna]

Thank you, very useful

[bjorn-spockeli]

Happy to help. If the answer solved your issue then I would appreciate if you caould mark the answer as correct/accepted by clicking the checkmark in the grey circle to the left of the answer.