[nRF52832] How to start/stop SAADC the right way?

RE: [nRF52832] How to start/stop SAADC the right way?

Jørgen Holmefjord — Wed, 25 Jul 2018 09:31:22 GMT

Please have a look at this answer. You will be facing the same issue when the CPU is blocked from handling the event when you halt it using the debugger.

RE: [nRF52832] How to start/stop SAADC the right way?

Bud Ward — Tue, 24 Jul 2018 19:31:56 GMT

I am having a similar problem when debugging with JLink. I am reading 8 channels 16 times each and averaging the results for each channel. This works fine as long as I do not stop and start execution. When restarted all analog channels are shifted one position. Repeatedly starting and stopping does not cause a further shift; they stay in their one-off condition until reset. I have tried explicitly waiting for busy to clear and doing an abort before initiating the next buffer_convert - no effect.

Using SDK_15.0.0.

This thread is quite old. Has a solution been found?

Thanks, Bud

RE: [nRF52832] How to start/stop SAADC the right way?

Jørgen Holmefjord — Wed, 06 Sep 2017 14:24:32 GMT

Are you having problems with double buffering? Could you post code showing how you setup, disable and enable the SAADC?

RE: [nRF52832] How to start/stop SAADC the right way?

Hamid — Thu, 31 Aug 2017 20:18:47 GMT

Hi Jørgen, I have the exact same problem on Starting/Stopping SAADC. Would you please post the possible solution? Thanks.

RE: [nRF52832] How to start/stop SAADC the right way?

Michael — Sun, 02 Apr 2017 08:33:39 GMT

I am using SDK 12.1.0. I will upload the project to MyPage.

RE: [nRF52832] How to start/stop SAADC the right way?

Jørgen Holmefjord — Fri, 31 Mar 2017 12:54:52 GMT

Which SDK version are you using? Are you able to share your project so I can do some testing on this? If you don't want to share it in public you can create a case and upload it on MyPage.

RE: [nRF52832] How to start/stop SAADC the right way?

Michael — Thu, 30 Mar 2017 12:53:42 GMT

Yes, I only get callbacks to the last buffer.

RE: [nRF52832] How to start/stop SAADC the right way?

Jørgen Holmefjord — Thu, 30 Mar 2017 12:51:10 GMT

Your method of starting the SAADC again sounds correct. Are you checking return codes of the calls to nrf_drv_saadc_buffer_convert() to see if it accepts the second call? Are you only getting callbacks when one of the buffers is filled?

RE: [nRF52832] How to start/stop SAADC the right way?

Michael — Wed, 29 Mar 2017 13:46:44 GMT

Also, I did use nrf_drv_saadc_uninit() at first - exactly like you said - stopping first the timer, disabling the PPI and checking using nrf_drv_saadc_is_busy() before calling nrf_drv_saadc_uninit().

However, when trying to restart it, I repeated the whole ADC initialization process (including channel init) and lost double buffering.

So, what is the recommended way to RESTART the ADC?

RE: [nRF52832] How to start/stop SAADC the right way?

Michael — Wed, 29 Mar 2017 13:35:26 GMT

Thanks Jørgen.

I managed to alleviate the problem greatly by using only nrf_drv_timer_disable() without calling nrf_drv_saadc_abort() as I did before.

However, when I try to increase the sampling rate to 12.5 KSPS and even 10 KSPS, while still maintaining a decimation factor of 8, I can see the channel shifting in real time - even without start/stop (using a monitoring application on an android phone).

With 8 KSPS, using only the timer to start/stop/ I haven't seen this yet, but maybe the bug just needs more time to manifest itself...

RE: [nRF52832] How to start/stop SAADC the right way?

Jørgen Holmefjord — Wed, 29 Mar 2017 13:29:41 GMT

Do you only see the shifted buffer if you stop the stop and start the SAADC? Some other users have reported swapped/shifted buffers when doing BLE activity. I see that there is a similar problem described in this thread, but it does not provide a solution. I will see if I can look further into this.

In general, nrf_drv_saadc_uninit() should be used to stop the SAADC. You could also try first stopping the timer calling the sample task, wait for the SAADC to be done (check using nrf_drv_saadc_is_busy() and then call nrf_drv_saadc_uninit().