Issues with timer driven ADC which results in improper readings

[arjun.binu]

ADC conversion of 3 channels (where DMA requests are performed in continuous mode) is triggered by Timer 3 Trigger out event. Timer 3 is made to follow a PWM generated by Timer 17 by assigning Timer 17 CCR1 to Timer 3 ARR. To validate the ADC readings, we tried varying Timer 17 PWM from 100 to lower values like 20. While doing so, I noticed that ADC readings are not proper and it varies in opposite direction after crossing a certain duty cycle of 50.

I have configured the ADC and timers using CubeMX and later used HAL library.

Your help and support is greatly appreciated.

Relevant code:

ADC initialization

 hadc1.Instance = ADC1;

 hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;

 hadc1.Init.Resolution = ADC_RESOLUTION_12B;

 hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;

 hadc1.Init.ScanConvMode = ADC_SCAN_ENABLE;

 hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;

 hadc1.Init.LowPowerAutoWait = DISABLE;

 hadc1.Init.LowPowerAutoPowerOff = DISABLE;

 hadc1.Init.ContinuousConvMode = DISABLE;

 hadc1.Init.NbrOfConversion = 3;

 hadc1.Init.DiscontinuousConvMode = DISABLE;

 hadc1.Init.ExternalTrigConv = ADC_EXTERNALTRIG_T3_TRGO;

 hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;

 hadc1.Init.DMAContinuousRequests = ENABLE;

 hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;

 hadc1.Init.SamplingTimeCommon1 = ADC_SAMPLETIME_160CYCLES_5;

 hadc1.Init.SamplingTimeCommon2 = ADC_SAMPLETIME_1CYCLE_5;

 hadc1.Init.OversamplingMode = DISABLE;

 hadc1.Init.TriggerFrequencyMode = ADC_TRIGGER_FREQ_HIGH;

Timer 3 initialization

 htim3.Instance = TIM3;

 htim3.Init.Prescaler = 1600 - 1;

 htim3.Init.CounterMode = TIM_COUNTERMODE_UP;

 htim3.Init.Period = 1;

 htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;

 htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;

 if (HAL_TIM_Base_Init(&htim3) != HAL_OK)

 {

   Error_Handler();

 }

 sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;

 if (HAL_TIM_ConfigClockSource(&htim3, &sClockSourceConfig) != HAL_OK)

 {

   Error_Handler();

 }

 if (HAL_TIM_OnePulse_Init(&htim3, TIM_OPMODE_SINGLE) != HAL_OK)

 {

   Error_Handler();

 }

 sMasterConfig.MasterOutputTrigger = TIM_TRGO_UPDATE;

 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;

Timer 17 initialization

 htim17.Instance = TIM17;

 htim17.Init.Prescaler = 1600 - 1;

 htim17.Init.CounterMode = TIM_COUNTERMODE_UP;

 htim17.Init.Period = 100 - 1;

 htim17.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;

 htim17.Init.RepetitionCounter = 0;

 htim17.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;

 if (HAL_TIM_Base_Init(&htim17) != HAL_OK)

 {

   Error_Handler();

 }

 if (HAL_TIM_PWM_Init(&htim17) != HAL_OK)

 {

   Error_Handler();

 }

 sConfigOC.OCMode = TIM_OCMODE_PWM1;

 sConfigOC.Pulse = 0;

 sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;

 sConfigOC.OCNPolarity = TIM_OCNPOLARITY_HIGH;

 sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;

 sConfigOC.OCIdleState = TIM_OCIDLESTATE_RESET;

 sConfigOC.OCNIdleState = TIM_OCNIDLESTATE_RESET;

 if (HAL_TIM_PWM_ConfigChannel(&htim17, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)

 {

   Error_Handler();

 }

 sBreakDeadTimeConfig.OffStateRunMode = TIM_OSSR_DISABLE;

 sBreakDeadTimeConfig.OffStateIDLEMode = TIM_OSSI_DISABLE;

 sBreakDeadTimeConfig.LockLevel = TIM_LOCKLEVEL_OFF;

 sBreakDeadTimeConfig.DeadTime = 0;

 sBreakDeadTimeConfig.BreakState = TIM_BREAK_DISABLE;

 sBreakDeadTimeConfig.BreakPolarity = TIM_BREAKPOLARITY_HIGH;

 sBreakDeadTimeConfig.BreakFilter = 0;

 sBreakDeadTimeConfig.AutomaticOutput = TIM_AUTOMATICOUTPUT_DISABLE;

 if (HAL_TIMEx_ConfigBreakDeadTime(&htim17, &sBreakDeadTimeConfig) != HAL_OK)

 {

   Error_Handler();

 }

This was implemented in STM32G030F6P6.

[KiptonM]

I do not see what channels you are reading.

Change:

hadc1.Init.SamplingTimeCommon1 = ADC_SAMPLETIME_160CYCLES_5;

 hadc1.Init.SamplingTimeCommon2 = ADC_SAMPLETIME_1CYCLE_5;

To the maximum value and see if it makes a difference.

The sample time may be too short which would give the response you describe. This is just a guess.

[S.Ma]

When possible route these interconnect signals through gpio and jumper wires to viee and debug better.

[FBL]

Hello @arjun.binu​,

I can see that you set   hadc1.Init.NbrOfConversion = 3;

Could you explain why ? Actually, this parameter refers to the number of ranks that will be converted within the group sequencer.

[Piranha]

The topic's first sentence literally says that he is converting 3 channels...

[arjun.binu · Accepted solution]

ADC readings are now proper after configuring Timer 3 properly so as to trigger ADC readings. This was done by selecting the "PWM Generation No output" for Channel 1.

This article helped me to properly configure it.

https://community.st.com/s/article/using-timers-to-trigger-adc-conversions-periodically

Thanks everyone.