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STM32H7 ADC dual mode simultanious mode problem



I am working with STM32H743, using ADC1 and 2 in dual simultanious mode, using DMA to store data from ADC_CDR (2 16 bit values) to memory, some hundred values in a stream in continuous mode. This works fine in general but I frequently see a missynchronisation between the two ADCs so that at the output of DMA I have in one 32bit word the lower half word from one ADC1 conversion of one point in time and in the upper half word the ADC2 conversion from the preceeding or succeeding point in time (I didn't check which of the two, but it is only one of them).

I read RM0433 ADC section up and down and could not find anything about that. It seems to be more related to hardware, that sometimes triggering DMA does not properly wait for both ADCs to be ready and have their data transfered to ACD_CDR. But it is not occuring or not from sample to sample but it is there for one complete data stream or not, so it seems to be set or not with every setting of ADSTART.

Here is my ADC init code:

#define SetBitMask(Var,BitMask) (Var|=(BitMask))

  SetBitMask (ADC1->CFGR, ADC_CFGR_RES_0);  // 14 bit
  SetBitMask (ADC2->CFGR, ADC_CFGR_RES_0);  // 14 bit
  ADC1->OFR1 = 0x8000 | (3 << ADC_OFR1_OFFSET1_CH_Pos); // offset for 16 bit signed values
  ADC2->OFR1 = 0x8000 | (4 << ADC_OFR1_OFFSET1_CH_Pos); // offset for 16 bit signed values
  ADC1->SQR1 = (3 << ADC_SQR1_SQ1_Pos) | (1-1); 
  ADC1->PCSEL = 1 << 3;
  ADC1->SMPR1 = 0; // 1.5 clk cycles sampling time
  ADC2->SQR1 = (4 << ADC_SQR1_SQ1_Pos) | (1-1);
  ADC2->PCSEL = 1 << 4;
  ADC2->SMPR1 = 0; // 1.5 clk cycles sampling time
  // the above settings result in:
  // for the two differential channels 3 and 4: 14 bit res, formatted as signed values -8192..8191, input res = 0.4mV diff / count
  // for the other = single ended channels: 14 bit res, formatted as unsigned values 0.. 16383, input res = 0.2mV / count
  // in continuous conversion mode (selected below) we get 1.5 + 7.5 = 9 clock cycles conversion time = 9 * 1/34,56 MHz = 260,417nsec corresp. to 3840 kSps
  // injected channels :
  // put them in the sequence so that ADC1 is in JDR1, ADC2 is in JDR2, ADC3 is in JDR3, where ADC1 = PA1, ADC2 = PA2, ADC3 = PA3
  ADC1->JSQR = (17 << ADC_JSQR_JSQ1_Pos) | (14 << ADC_JSQR_JSQ2_Pos) | (15 << ADC_JSQR_JSQ3_Pos) | (3-1);
  ADC1->PCSEL |= (1 << 14) | (1 << 15) | (1 << 17);
  ADC1->SMPR2 = (4 << ADC_SMPR2_SMP14_Pos) | (4 << ADC_SMPR2_SMP15_Pos) | (4 << ADC_SMPR2_SMP17_Pos); // 4 = 32.5 clk cycles, slow channels: max 1Msps
  SetBitMask (ADC12_COMMON->CCR, ADC_CCR_DUAL_0 | ADC_CCR_DAMDF_1); // dual mode with output to ADC_CDR
  SetBitMask (ADC1->CFGR, ADC_CFGR_CONT | ADC_CFGR_DMNGT_0  | ADC_CFGR_DMNGT_1); // ADC in continuous mode and in DMA circular mode

Is there any information about that?

Anybody experienced the same? - and solved it 😉

Thanks a lot


Mikhail Z
Senior II

Did you use ver. Y or V of the chip?

Hi Mikhail,
I have rev V, sorry, I forgot to mention.
Mikhail Z
Senior II


Associate II

I have the same problem. the DMA transfer seems to be triggered by the master EOC.

When I select the same sample time for master and slave the DMA reads the previous slave sample. When the slave sample time is shorter than the master sample time it works correctly. When the sample time of the slave is larger than the master sample time the DMA transfer is triggered at the master EOC, so way before the slave is finished.

I'm using rev V too. and am using the ChibiOS HAL. Only regular simultaneous mode, happens when either sampling 1 or more channels. Figure 202 of RM0433 (page 996) very clearly shows that the DMA request should only be sent after both master and slave EOC.

It is a bit unclear from the reference manual when the 32 bit format on CDR2 is used and when the 16 bit format on CDR. Maybe it has to do something with that?

I didn't try the Cube HAL yet, do people get correct results with that? Or is there an error in the silicon?

Do you use 1 or 2 DMA channels?

1 DMA channel, getting data from ADC12_CDR,

DMNGT = 11: DMA Circular Mode selected

DAMDF = 10: Data formatting mode for 32 down to 10-bit resolution,

DUAL = 00110: Regular simultaneous mode only

I don't remember having any problems when used with 2 DMA channels, so you can try that.

Using 2 DMA channels is an option, using no DMA at all is also viable in my case.

However since the ChibiOS HAL uses one DMA channel (and that seems the most efficient) it would be the easiest to get that working.

If it doesn't work as stated it would be nice to update the reference manual that the ADC1 (master) sample time should be more than the ADC2 (slave) sample time. (which makes single DMA channel mode kinda useless)

The manual says that "In regular simultaneous mode, one must convert sequences with the same length and

inside a sequence, the N-th conversion in master ans slave must be configured with the

same sampling time."