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