ADC samples get corrupted at end of sampling series

Posted on August 04, 2013 at 13:51

MCU: Cortex M3, STM32F103VC

I am using a DDS to generate a constant sinusoidal wave. I am sampling this wave and the last 160 samples are almost all garbage. No matter if I sample 7000 samples or 360, the last 160 is way off. I have ruled out that DDS is the problem by sampling the MCU 3V3 pin and it still gives error on the last 160 samples. I was wondering if anyone else have had similar problem or see any error in my code? (code shown below are a simplified/shortcut version of whatI am using, but is working and gives the same corrupted data) Here are some sample images:

http://imgur.com/CeMv0H4

http://imgur.com/kCOLbXG

http://imgur.com/8kiTWTD

EDITstart: I expanded the

ADCdata

array to be initialized as

ADCdata

[7200+160] instead of

ADCdata

[7200]when sampling 7200 and I did not get corrupted data. This might mean the the ADC is not the one corrupting the data but something else? Don't see what it can be though...

http://imgur.com/nDStvBD

EDITfinished. Here are relevant code:

void ADC_Initialization(void) 
{ 
GPIO_InitTypeDef GPIO_InitStructure; 
ADC_InitTypeDef ADC_InitStructure; 
//ADC clk = APB2 clk / 6 = 72MHz/6 = 12MHz. MAX 14MHz. 
RCC_ADCCLKConfig(RCC_PCLK2_Div6); 
RCC_APB2PeriphClockCmd( (RCC_APB2Periph_ADC1 | RCC_APB2Periph_GPIOC) , ENABLE); 
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0; 
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; 
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN; 
GPIO_Init(GPIOC, &GPIO_InitStructure); 
//DMA_ADC_Initialization(); 
//ADC_InitStructure.ADC_Mode = ADC_Mode_RegSimult; 
ADC_InitStructure.ADC_Mode = ADC_Mode_Independent; 
ADC_InitStructure.ADC_ScanConvMode = DISABLE; 
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE; 
//ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1; 
ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None; 
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right; 
ADC_InitStructure.ADC_NbrOfChannel = 1; 
ADC_Init(ADC1, &ADC_InitStructure); 
ADC_RegularChannelConfig(ADC1, ADC_Channel_10, 1, ADC_SampleTime_7Cycles5); 
//ADC_DMACmd(ADC1, ENABLE); 
//Enable timer 1 compare as external trigger 
//ADC_ExternalTrigConvCmd(ADC1, ENABLE); 
//Enable ADC1 
ADC_Cmd(ADC1, ENABLE); 
/* 
//Reset ADC1 calibration register 
ADC_ResetCalibration(ADC1); 
//Wait until ADC1 reset is done 
while(ADC_GetResetCalibrationStatus(ADC1) == SET); 
//Start ADC1 calibration 
ADC_StartCalibration(ADC1); 
//Wait until ADC1 calibration is done 
while(ADC_GetCalibrationStatus(ADC1) == SET); 
*/ 
//DMA_ITConfig(DMA1_Channel1, DMA_IT_TC, ENABLE); 
} 
void TIMER1_Init(void) 
{ 
NVIC_InitTypeDef NVIC_InitStructure; 
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure; 
//Enable Timer 2 clock 
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE); 
//Base 
TIM_TimeBaseStructure.TIM_Prescaler = 0; 
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; 
TIM_TimeBaseStructure.TIM_Period = 60167; 
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; 
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure); 
TIM_ARRPreloadConfig(TIM1, ENABLE); 
//Register with Nested Vectored Interrupt Controller (NVIC). 
NVIC_InitStructure.NVIC_IRQChannel = TIM1_CC_IRQn; 
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0B; 
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0B; 
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; 
NVIC_Init(&NVIC_InitStructure); 
//Clear timer 
TIM_SetCounter(TIM1, 0); 
//Interrupt 
TIM_ITConfig(TIM1, TIM_IT_CC1, ENABLE); 
} 
void TIMER1_Enable(void) 
{ 
//Clear timer 
TIM_SetCounter(TIM1, 0); 
//Enable timer 
TIM_Cmd(TIM1, ENABLE); 
} 
void TIMER1_Disable(void) 
{ 
//Disable timer 
TIM_Cmd(TIM1, DISABLE); 
} 
void TIM1_CC_IRQHandler(void) 
{ 
uint16_t i; 
static uint16_t j = 0; 
LED(LED1, ON); 
ADC_SoftwareStartConvCmd(ADC1, ENABLE); 
while( !ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC) ); 
ADCdata[j] = ADC_GetConversionValue(ADC1); 
j++; 
if(j == 7200) 
{ 
TIMER1_Disable(); 
printf(''_plotEnable\n''); 
for(i = 0; i < 7200; i++) 
{ 
printf(''%u, '', (uint16_t) (ADCdata[i] & 0x0FFF)); 
} 
printf(''\n''); 
} 
//Clear timer 1 compare interrupt 
TIM_ClearITPendingBit(TIM1, TIM_IT_CC1); 
} 
void main(void) 
{ 
TIMER1_Enable(); 
while(TRUE) 
{ 
} 
}

#adc-timer-cortexm3