Empty report with Nordic Distance Toolbox and high precision calculation

[phemid]

Hi

I use the nRF connect SDK v2.0 installed with the toolchain manager and tried the distance measurement which works fine but doesn't use the high precision mode. I changed in the file 'dm.c' the function call from:

nrf_dm_calc(&report);

to:

float distance = nrf_dm_high_precision_calc(&report);
report.distance_estimates.mcpd.ifft = distance;

It works after I set some linker flags but the report is empty (all values are 0) so I currently use the ifft variable as you can see to print out the distance in the callback function. Is it normal that the report is empty or is it fixed in a newer version?

[Michal]

Hello,

Yes, that's normal. The nrf_dm_high_precision_calc() does not fill out all the data like nrf_dm_calc(), it just returns a float directly.

The current example is made around nrf_dm_calc(), which is why it may be a bit confusing when trying to use the high precision function.

Best regards,
Michal

[phemid]

Hello,

thank you for the clarification, i modified the printk() call. One last question: should the config parameters (CONFIG_DM_INITIATOR_RANGING_WINDOW_US, CONFIG_DM_REFLECTOR_RANGING_WINDOW_US, ...) be increased because nrf_dm_high_precision_calc() need more calculation time and what values should then be used?

[Michal]

Hello,

Yes, you should increase CONFIG_DM_MIN_TIME_BETWEEN_TIMESLOTS_US.

As for the values, I have contacted the developers and got the execution time graphs. Both test were done on nRF52833, so it should be similar for nRF52840.
Just be wary that they were made in a static environment. In a dynamic, wireless environment the values may differ, so just treat them as estimates.

Here is one for nrf_dm_calc():

And one for nrf_dm_high_precision_calc():

So maybe something like 100000+ µs would be a good value to start with.

Looks like there is also some work on including the high precision calculation into the NCS sample, but I don't have any status or estimates on that other than this pull request.

Best regards,

Michal