KEA ADC FIFO

[MichaelBMiner]

Hello,

I am trying to add a new channel to my ADC polling. Adding this new channel to the FIFO breaks everything and I am unsure why. I am trying to measure the internal chip temperature if an I2C connected temperature sensor is not found. 

When initializing my ADC I set my FIFO depth to 5 then add the 5 channels to read.

	ADC_SetFifoDepth(ADC_FIFO_LEVEL5);
	ADC_SetChannel(ADC_CHANNEL_AD10);
	ADC_SetChannel(ADC_CHANNEL_AD13);
	ADC_SetChannel(ADC_CHANNEL_AD5);
	ADC_SetChannel(ADC_CHANNEL_AD14);
	ADC_SetChannel(ADC_CHANNEL_TEMPERATURE);

If I add the first 4, or the last 1 it all works as expected. The issue is when I add them all together. 

Before this step I check for the I2C temp sensor. If not found I read my Vbg to calculate Vdd as per AN3031. 

	if(!i2c_temp_sensor_found) {
		I2C0_Disable();
		ADC_EnablePCM_BG();
		ADC_SetFifoDepth(ADC_FIFO_LEVEL2);
		ADC_SetChannel(ADC_CHANNEL_BANDGAP);
		ADC_SetChannel(ADC_CHANNEL_BANDGAP);
		keazxx_temp_init();
		ADC_SetFifoDepth(ADC_FIFO_DISABLE);
	}

In keazxx_temp_init() I retrieve 2 samples from the FIFO. This should empty the FIFO. Periodically I set my FIFO channels to trigger a new conversion. My ADC IRQ runs as expected. Can anyone see any issues with my setup? Is my FIFO not being cleared correctly? Why when I add one more ADC point does everything go haywire? 

Edit 1: I can confirm that my FIFO is empty at the end of my IRQ routine. I am not only reading some of my data. I am reading it all. 

Edit 2: At the end of keazz_init_temp my FIFO is also empty. 

Edit 3: I have set my FIFO to AND all compare registers. ADC_SC4 -> ACFSEL = 1 This has no effect. 

Edit 4: I have confirmed that my FIFO is full when my ADC IRQ occurs and empty after I read the ADC->R register 5 times.

Edit 5: The issue has been resolved by setting the Long Sample Time Configuration. My only remaining question is how do I know which of the two slopes to use? When calculating the temp I am given two slops one for temps greater than 25 and one for temps less than 25. If I have not calculated the temp, how do I know which to use?

[PabloAvalos]

Hi, Michael

Hoping you are excellent.

I would like to know which AD channel are you using for the temperature sensor (ADC_CHANNEL_TEMPERATURE) ?

Also, please refer to this reference manual, in the section 3.8.1.4 page number 78-79 KEA128 Reference Manual.

Regarding your last question, about the slopes, you can read this thread, so it can be helpful: https://community.nxp.com/t5/Kinetis-Microcontrollers/On-chip-temperature-Calculations/m-p/465611

Please let me know if you have more questions.

Best Regards,

Pablo Avalos.