adc1 and dma reliability issue

Posted on May 17, 2011 at 12:40

Hi Andy.

Can you post here the revelant parts of your code?

Thanks,

Steve.

Posted on May 17, 2011 at 12:40

After a few million scans my set of scan data shifts (circularly) one channel. It stays shifted until I reset the processor.

This is an unlivable bug, and I can't reliably detect if the shift has occurred just be looking at the data.

I am using DMA to store the conversions. Since the data shifts circularly (DMA only writes to the correct addresses) it seems that the adc sequencer must be at fault.

I trigger the scan via the software start bit, called from a 1kHz periodic timer routine (the system timer tick). I use bitband access for the start scan bit (cr2 bit 22).

I set the settling time to the maximum (to minimize one channel's value from affecting another's).

I process the scanned values in the DMA ISR.

When I stop the processor after the fault all of the ADC configuration values are unchanged from my initialization.

Since a single software conversion is actually a scan of 1 channel I have no confidence that asking for conversions one at a time is going to solve the problem.

Am I alone in my using the adc in this way?

Am I alone in needing the hardware to work correctly more than 30 million times in a row?

----

The only truly weird thing I do is to use structs for access to the adc controller registers. Using a struct requires that the controller register support single byte accesses, and the manual doesn't state which registers require 16 or 32 bit access. Some peripherals don't work with 8 bit accesses but I can't imagine that being intermittent, and after configuration is completed I use bit-band access so the use of a struct should be moot.

Posted on May 17, 2011 at 12:40

my bad,

I was running the ADC at 16MHz, its max frequency is 14MHz.

I finally noticed a comment in my code:

//todo: set the adc prescaler.

Posted on May 17, 2011 at 12:40

Andy,

Are you setting the continuous bit (Bit 1 - CONT) in ADC_CR2?

If so then you shouldn't keep hitting the ADC with a SWSTART every 1ms. Just once will do. I'll assume there is no issue with the structs you're using (since you've checked the register contents with a debugger)

Have the DMA automatically reload its counter and use continuous conversions for the ADC and then it's pretty much hands off after that.

I'm scanning with dual-convertors (8 channels total) and using the DMA to store 4 sets of conversions for each channel and it has never gone out of sync.

Ryan