ADC sample rate for STM32H725
Hello,
I am sampling two signals using ADC1 in master, and ADC2 as a slave.
For this i am using ADC1 Input3 and ADC2 Input 5, with DMA filling the 32bit buffer, with a buffer size of 2048.
Bellow are some setings how the master/slave is configured in a simplified manner
AdcHandle_master.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV4;//ADC_CLOCK_ASYNC_DIV4; // Asynchronous clock mode, input ADC clock divided by 4
AdcHandle_master.Init.Resolution = ADC_RESOLUTION_16B; // 16-bit
AdcHandle_master.Init.ScanConvMode = DISABLE; // Sequencer disabled (ADC conversion on only 1 channel: channel set on rank 1)
AdcHandle_master.Init.EOCSelection = ADC_EOC_SINGLE_CONV; // EOC flag picked-up to indicate conversion end
AdcHandle_master.Init.LowPowerAutoWait = DISABLE; // Auto-delayed conversion feature disabled
AdcHandle_master.Init.ContinuousConvMode = ENABLE; // Continuous mode to have maximum conversion speed (no delay between conversions)
AdcHandle_master.Init.NbrOfConversion = 1; // Parameter discarded because sequencer is disabled
AdcHandle_master.Init.DiscontinuousConvMode = DISABLE; // Parameter discarded because sequencer is disabled
AdcHandle_master.Init.NbrOfDiscConversion = 1; // Parameter discarded because sequencer is disabled
AdcHandle_master.Init.ExternalTrigConv = ADC_SOFTWARE_START; // Software start to trigger the 1st conversion manually, without external event
AdcHandle_master.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE; // Parameter discarded because trigger of conversion by software start (no external event)
AdcHandle_master.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DMA_CIRCULAR; // DMA circular mode selected
AdcHandle_master.Init.Overrun = ADC_OVR_DATA_OVERWRITTEN; // DR register is overwritten with the last conversion result in case of overrun
AdcHandle_master.Init.OversamplingMode = DISABLE; // No oversampling
// Configuration of ADC (slave) init structure: ADC parameters and regular group
AdcHandle_slave.Instance = ADCy;
AdcHandle_slave.Init = AdcHandle_master.Init;
AdcHandle_slave.Init.ContinuousConvMode = DISABLE;
AdcHandle_slave.Init.ExternalTrigConv = ADC_SOFTWARE_START;
sConfig.Rank = ADC_REGULAR_RANK_1; // Rank of sampled channel number ADCx_CHANNEL
sConfig.SamplingTime = SAMPLING_TIME;
sConfig.SingleDiff = ADC_SINGLE_ENDED; // Single-ended input channel
sConfig.OffsetNumber = ADC_OFFSET_NONE; // No offset subtraction
sConfig.Offset = 0; // Parameter discarded because offset correction is disabled
sConfig.Channel = ADCx_CHANNELa; // Sampled channel number
sConfig.Channel = ADCy_CHANNELa;
MultiModeInit.Mode = ADC_DUALMODE_REGSIMULT;
MultiModeInit.DualModeData = ADC_DUALMODEDATAFORMAT_32_10_BITS; // ADC and
DMA configured in resolution 32 bits to match with both ADC master and slave resolution
MultiModeInit.TwoSamplingDelay = ADC_TWOSAMPLINGDELAY_1CYCLE;
The clock for the ADC is comming from PLL2 at 88MHZ
Then this clock is divided by 4 via ADC_CLOCK_ASYNC_DIV4. So i would expect the adc clock to be at 22mhz
The ADC is configure to sample at 8.5 cycles ( +7.5 default ones) for a 16bit resolution.
So what would be the adc sample speed? 22mhz / ( 8.5+7.5 cycles) = 1.375Msps?
I ask this because i am not abble to capture a 1000hz sinewave signal.
The main goal here, is to obtain 2Msps with this settup
But if i use ADC_CLOCK_ASYNC_DIV2 then this yelds 2.75 Msps, and i am able to perfectly measure the sine signal.
But why is this? I am missing something? How should i estimate the sample rate for the ADC?