[参考译文] TMS320F28379D：ADC 误差

//#############################################################################
//
// FILE:   adc_ex2_soc_epwm.c
//
// TITLE:  ADC ePWM Triggering
//
//! \addtogroup driver_example_list
//! <h1>ADC ePWM Triggering</h1>
//!
//! This example sets up ePWM1 to periodically trigger a conversion on ADCA.
//!
//! \b External \b Connections \n
//!  - A0 should be connected to a signal to convert
//!
//! \b Watch \b Variables \n
//! - \b adcAResults - A sequence of analog-to-digital conversion samples from
//!   pin A0. The time between samples is determined based on the period
//!   of the ePWM timer.
//!
//
//#############################################################################
//
// $Release Date: $
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//#############################################################################
//

//
// Included Files
//
#include "driverlib.h"
#include "device.h"

//
// Defines
//
#define RESULTS_BUFFER_SIZE     3000
#define EX_ADC_RESOLUTION       12
// 12 for 12-bit conversion resolution, which supports (ADC_MODE_SINGLE_ENDED)
// Sample on single pin (VREFLO is the low reference)
// Or 16 for 16-bit conversion resolution, which supports (ADC_MODE_DIFFERENTIAL)
// Sample on pair of pins (difference between pins is converted, subject to
// common mode voltage requirements; see the device data manual)

//
// Globals
//
volatile uint16_t adcAResults[RESULTS_BUFFER_SIZE];   // Buffer for results
uint16_t index;                              // Index into result buffer
uint16_t i;
volatile uint32_t sum_of_adc_data;
volatile uint32_t avg_adc_value, diff_value;
volatile uint16_t bufferFull;                // Flag to indicate buffer is full
volatile uint32_t Max_adc_value = 0x00000000;
volatile uint32_t Min_adc_value = 0xFFFFFFFF;
//
// Function Prototypes
//
void initADC(void);
void initEPWM(void);
void initADCSOC(void);
__interrupt void adcA1ISR(void);

//
// Main
//
void main(void)
{
    //
    // Initialize device clock and peripherals
    //
    Device_init();

    //
    // Disable pin locks and enable internal pullups.
    //
    Device_initGPIO();

    //
    // Initialize PIE and clear PIE registers. Disables CPU interrupts.
    //
    Interrupt_initModule();

    //
    // Initialize the PIE vector table with pointers to the shell Interrupt
    // Service Routines (ISR).
    //
    Interrupt_initVectorTable();

    //
    // Interrupts that are used in this example are re-mapped to ISR functions
    // found within this file.
    //
    Interrupt_register(INT_ADCA1, &adcA1ISR);

    //
    // Set up the ADC and the ePWM and initialize the SOC
    //
    initADC();
    initEPWM();
    initADCSOC();

    //
    // Initialize results buffer
    //
    for(index = 0; index < RESULTS_BUFFER_SIZE; index++)
    {
        adcAResults[index] = 0;
    }

    index = 0;
    bufferFull = 0;

    //
    // Enable ADC interrupt
    //
    Interrupt_enable(INT_ADCA1);

    //
    // Enable Global Interrupt (INTM) and realtime interrupt (DBGM)
    //
    EINT;
    ERTM;

    //
    // Loop indefinitely
    //
    while(1)
    {
        //
        // Start ePWM1, enabling SOCA and putting the counter in up-count mode
        //


        EPWM_enableADCTrigger(EPWM1_BASE, EPWM_SOC_A);
        EPWM_setTimeBaseCounterMode(EPWM1_BASE, EPWM_COUNTER_MODE_UP);

        //
        // Wait while ePWM1 causes ADC conversions which then cause interrupts.
        // When the results buffer is filled, the bufferFull flag will be set.
        //
        if(bufferFull == 3){
            EPWM_disableADCTrigger(EPWM1_BASE, EPWM_SOC_A);
            EPWM_setTimeBaseCounterMode(EPWM1_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);

            for(i = 0; i < RESULTS_BUFFER_SIZE; i++){
                if(adcAResults[i] > Max_adc_value){
                    Max_adc_value = adcAResults[i];
                }
                if(adcAResults[i] < Min_adc_value){
                    Min_adc_value = adcAResults[i];
                }
                sum_of_adc_data += adcAResults[i];
            }
            avg_adc_value = sum_of_adc_data / RESULTS_BUFFER_SIZE;
            diff_value = 2121 - avg_adc_value;

            ESTOP0;
        }
//        while(bufferFull == 0)
//        {
//        }
//        bufferFull = 0;     // Clear the buffer full flag
//
//        //
//        // Stop ePWM1, disabling SOCA and freezing the counter
//        //
//        EPWM_disableADCTrigger(EPWM1_BASE, EPWM_SOC_A);
//        EPWM_setTimeBaseCounterMode(EPWM1_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);

        //
        // Software breakpoint. At this point, conversion results are stored in
        // adcAResults.
        //
        // Hit run again to get updated conversions.
        //
        //ESTOP0;
    }
}

//
// Function to configure and power up ADCA.
//
void initADC(void)
{
    
    //
    // Set ADCDLK divider to /4
    //
    ADC_setPrescaler(ADCA_BASE, ADC_CLK_DIV_2_0);

    //
    // Set resolution and signal mode (see #defines above) and load
    // corresponding trims.
    //
#if(EX_ADC_RESOLUTION == 12)
    ADC_setMode(ADCA_BASE, ADC_RESOLUTION_12BIT, ADC_MODE_SINGLE_ENDED);
#elif(EX_ADC_RESOLUTION == 16)
    ADC_setMode(ADCA_BASE, ADC_RESOLUTION_16BIT, ADC_MODE_DIFFERENTIAL);
#endif

    //
    // Set pulse positions to late
    //
    ADC_setInterruptPulseMode(ADCA_BASE, ADC_PULSE_END_OF_CONV);

    //
    // Power up the ADC and then delay for 1 ms
    //
    ADC_enableConverter(ADCA_BASE);
    DEVICE_DELAY_US(1000);
}

//
// Function to configure ePWM1 to generate the SOC.
//
void initEPWM(void)
{
    //
    // Disable SOCA
    //
    EPWM_disableADCTrigger(EPWM1_BASE, EPWM_SOC_A);

    //
    // Configure the SOC to occur on the first up-count event
    //
    EPWM_setADCTriggerSource(EPWM1_BASE, EPWM_SOC_A, EPWM_SOC_TBCTR_U_CMPA);
    EPWM_setADCTriggerEventPrescale(EPWM1_BASE, EPWM_SOC_A, 1);

    //
    // Set the compare A value to 1000 and the period to 1999
    // Assuming ePWM clock is 100MHz, this would give 50kHz sampling
    // 50MHz ePWM clock would give 25kHz sampling, etc. 
    // The sample rate can also be modulated by changing the ePWM period
    // directly (ensure that the compare A value is less than the period). 
    //
    EPWM_setCounterCompareValue(EPWM1_BASE, EPWM_COUNTER_COMPARE_A, 1000);
    EPWM_setTimeBasePeriod(EPWM1_BASE, 1999);

    //
    // Set the local ePWM module clock divider to /1
    //
    EPWM_setClockPrescaler(EPWM1_BASE,
                           EPWM_CLOCK_DIVIDER_1,
                           EPWM_HSCLOCK_DIVIDER_1);

    //
    // Freeze the counter
    //
   // EPWM_setTimeBaseCounterMode(EPWM1_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);
}

//
// Function to configure ADCA's SOC0 to be triggered by ePWM1.
//
void initADCSOC(void)
{
    //
    // Configure SOC0 of ADCA to convert pin A0. The EPWM1SOCA signal will be
    // the trigger.
    // - For 12-bit resolution, a sampling window of 15 (75 ns at a 200MHz
    //   SYSCLK rate) will be used.  For 16-bit resolution, a sampling window
    //   of 64 (320 ns at a 200MHz SYSCLK rate) will be used.
    // - NOTE: A longer sampling window will be required if the ADC driving
    //   source is less than ideal (an ideal source would be a high bandwidth
    //   op-amp with a small series resistance). See TI application report
    //   SPRACT6 for guidance on ADC driver design.
    //

#if(EX_ADC_RESOLUTION == 12)
    ADC_setupSOC(ADCA_BASE, ADC_SOC_NUMBER0, ADC_TRIGGER_EPWM1_SOCA,
                 ADC_CH_ADCIN0, 128);
#elif(EX_ADC_RESOLUTION == 16)
    ADC_setupSOC(ADCA_BASE, ADC_SOC_NUMBER0, ADC_TRIGGER_EPWM1_SOCA,
                 ADC_CH_ADCIN0, 64);
#endif

    //
    // Set SOC0 to set the interrupt 1 flag. Enable the interrupt and make
    // sure its flag is cleared.
    //
    ADC_setInterruptSource(ADCA_BASE, ADC_INT_NUMBER1, ADC_SOC_NUMBER0);
    ADC_enableInterrupt(ADCA_BASE, ADC_INT_NUMBER1);
    ADC_clearInterruptStatus(ADCA_BASE, ADC_INT_NUMBER1);
}

//
// ADC A Interrupt 1 ISR
//
__interrupt void adcA1ISR(void)
{

    //
    // Add the latest result to the buffer
    //
    adcAResults[index++] = ADC_readResult(ADCARESULT_BASE, ADC_SOC_NUMBER0);

    //
    // Set the bufferFull flag if the buffer is full
    //

    if(RESULTS_BUFFER_SIZE <= index)
    {
        index = 0;
        bufferFull += 1;
    }

    //
    // Clear the interrupt flag
    //
    ADC_clearInterruptStatus(ADCA_BASE, ADC_INT_NUMBER1);

    //
    // Check if overflow has occurred
    //
    if(true == ADC_getInterruptOverflowStatus(ADCA_BASE, ADC_INT_NUMBER1))
    {
        ADC_clearInterruptOverflowStatus(ADCA_BASE, ADC_INT_NUMBER1);
        ADC_clearInterruptStatus(ADCA_BASE, ADC_INT_NUMBER1);
    }

    //
    // Acknowledge the interrupt
    //
    Interrupt_clearACKGroup(INTERRUPT_ACK_GROUP1);
}