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Jakub Konieczny
Jakub Konieczny
Associate
May 9, 2018 10:54 AM UTC
Question

STM32F3 simultaneous ADC conversions

Posted on May 09, 2018 at 12:54

Hi.

I want to do do ADC conversions on all 3 ADCs simultaneous: they should be done in the same time. How should I achieve that?

1. With DMA? I can do multichannel conversions, but they are not simultaneous. When I start `HAL_ADC_Start_DMA(&hadc1, adcData[0], 5);` 3 times, it looks like it does conversions for each ADC synchronous. MultiMode is only for 2 DMA channels and I need to do 3 measurements simultaneous.

2. With IRQ: start conversions with interrupts and catch them all, and then when I get all 3 start them again?

3. Mix them?

#stm32f3 #dma #adc
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8 replies

S.Ma
S.Ma
Principal
May 9, 2018 12:14 PM UTC
Posted on May 09, 2018 at 14:14

Normally the result of an ADC conversion is pushed onto a register. This value is available until the ADC took the time to finish converting the next conversion and overwrite the register.

To synchronize all 3 ADC only require to share the same start of conversion. Reading the 3 registers don't have to be done at the same CPU cycle speed. Thoughts?

Tesla DeLorean
Tesla DeLorean
Guru
May 9, 2018 12:16 PM UTC
Posted on May 09, 2018 at 14:16

Seem to think you can have ADC1&2 and ADC3&4 share a common TIM trigger, thus effecting paced and simultaneous acquisitions.

Likely will need to use two DMA, so two separate arrays. I know I built a 4-UP ADC with the F3+SPL

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Jakub Konieczny
Jakub KoniecznyAuthor
Associate
May 9, 2018 2:57 PM UTC
Posted on May 09, 2018 at 14:57

I have only one free DMA for this.

This CPU has 3 SDADC (forgot to mention it's Sigma Delta, if that matters). So just start all 3 with interrupts in continous mode and read results in interrupt handler? Is it ensured that the measurements will not dissynchronize? I mean if I start 3 SDADCs in the same time (+- few CPU cycles, doesn't matter), time difference between each next measurements will be constant? After 5 seconds, every SDADC will do same amount of measurements?

S.Ma
S.Ma
Principal
May 9, 2018 7:05 PM UTC
Posted on May 09, 2018 at 19:05

Check out the core speed SYSCLK in MHz and each ADC Sampling frequency. Are all ADC sharing the same sampling frequency?

kader ben
kader ben
Associate
May 13, 2018 7:46 PM UTC
Posted on May 13, 2018 at 21:46

hello please, I have a robotics project where I'm forced to use a stm32f3, but I do not know about stm32, I need a basic code to perform the digital analog conversion a continuous signal through pin PA0 ( first adc_in), to understand this part. thank you in advance.

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