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STM32H743 ADC DMA performance calculations

Question asked by Baker Ngan on Mar 9, 2018
Latest reply on Mar 9, 2018 by Darius B

So I am working with an STM32H743 MCU. I have it setup so I am using ADC1 to do a continuous sample of channel 3 and 10 over DMA. All works fine and I get a dma interrupt for conversion complete every ~10 usec. However when I use ADC3 now and sample channel 5 and 18 over DMA as well, my conversion time for ADC1 has increased to almost twice the amount, up to ~20 usec. I have tried using ADC2 as well and ADC1 and ADC2 in simultaneous mode, however I get a similar result. If I use 2 ADCs, shouldn't those 2 conversions happen in parallel? I have seperated out ADC1 and ADC3 to different DMA controllers as well ( one using DMA1 channel 0 and one using DMA2 channel3). Results of the conversion look fine so, I am sure it is configured correctly, however I don't understand why adding a separate ADC would increase the time of the other ADC.