I am seeing a problem using the nRF52 SAADC with two analog channels enabled in scan mode. Essentially, channel 0 is measuring an analog signal with gain ~= 15 while channel 1 is measuring the same signal with gain = 1.
The ADC is sampled in scan mode at 4kHz into a buffer that holds 2048 samples for each channel. When I receive the interleaved buffer, I usually see that the channel 0 ADC data is at address offset 0, 4, 8, etc and the channel 1 data is at address offset 2, 6, 0xa, etc.
Unfortunately, sometimes these channels are swapped. (ie. the channel 0 data is at address offset 2, 6, 0xa,... and the channel 1 data is at address offsets 0, 4, 8, ....).
Is there anything I can do to ensure that channel 0 data starts at offset 0 and channel 1 data starts at offset 2?
Here is a printf from the code that shows the peak value of each channel as well as the buffer address:
As you can see, the first two captures have the higher gain signal in the 0 offset position as expected. However, the third capture has the lower gain signal in the 0 offset position.
Is there something I need to do to the EasyDMA module to reset between captures? Currently, I am just calling nrf_drv_saadc_buffer_convert() to start a new capture.
I am using SDK version 11.0.0 and S132 version 2.0.1