ADC and DMA on STM32F303

[DetlefS]

Hi,

I run ADC1 with DMA on my STM32F303RE with 72MHz clock. 

I take the number of samples flowing into the circular buffer per timeunit.  I calculate a sample freq. of 1.305 Megasamples per second Ms/s.

When I look at the sampled known signal I calculate a sample frequency of 1.518Ms/s.

I'm losing samples somewhere !? 

Where? Is it due to ADC or DMA? 

ADC setup: Independent mode,Synchronous clock mode divided by 4, 12Bit, scan disable, continuous enable, enable regular conversions enable, 

DMA setup: ADC1 DMA1 CHANNEL1, circular buffer 15*1024*uint16_t, increment address memory, half word

THX

Cheers

Detlef

[Simon V.]

Hello,

If ADC frequency is 72MHz/4 and sampling duration is 1.5 cycles and conversion duration 12.5 for 12bits then STM32F3 sampling rate is (72/4) / (1.5+12.5) = 1.28e6 samples per seconds while you are calculating 1.305 => can you please share your formula ?

How do you proceed to calculate the ADC sampling rate ? Are you using a sinus or a square waveform ?

Thanks in advance,

Regards,

Simon

[DetlefS]

Hi Simon,

I lost track how I ended up with 1.305 Ms/s. 

>>How do you proceed to calculate the ADC sampling rate ? Are you using a sinus or a square waveform ?

I sampled DCF77, which is 77.5kHz with better than 1e-8 accuracy. I got the sample freq. from my PLL.

I solved it by using a timer to kick the ADC. This setup is good enough to calculate the uC clock to be off by 144Hz ;)).

Big fun.

Cheers

Detlef