Electronic – Understanding ADC – TMS32F28027

I am new to microcontrollers. I modified the Adc_Soc Example, such that CPU Timer 0 triggers ADCINA7. CPU Timer 0 is configured with 60MHz and period is 2 seconds. Also I increment a variable(LoopCount) inside adc_isr.

My doubt is, if I am triggering the SOC8 with CPU Timer 0 for every 2 seconds, then the variable(LoopCount) should increment every two seconds. But here it increases rapidly in 1000s within a second. Why is it so? And please correct me if I am wrong.

Edit 1 : Instead of declaring and defining the Interrupt _isr in the main.c, I used the f2802x_defaultisr.c and now the ADC register value is updated every 2 seconds. But still I don't know where I went wrong with the previous code(interrupt_isr in main.c). Please help me.

#include "DSP28x_Project.h"     // Device Headerfile and Examples Include File
// Prototype statements for functions found within this file.
interrupt void adc_isr(void);
//interrupt void cputimer0_isr(void);
void Adc_Config(void);

// Global variables used in this example:
volatile uint16_t Voltage;
uint16_t LoopCount;


main()
{

    // WARNING: Always ensure you call memcpy before running any functions from RAM
// InitSysCtrl includes a call to a RAM based function and without a call to
// memcpy first, the processor will go "into the weeds"
#ifdef _FLASH
memcpy(&RamfuncsRunStart, &RamfuncsLoadStart, (size_t)&RamfuncsLoadSize);
#endif

Step 1. Initialize System Control:
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the DSP2803x_SysCtrl.c file.
InitSysCtrl();


// Step 2. Initialize GPIO:
// This example function is found in the f2802x_Gpio.c file and
// illustrates how to set the GPIO to it's default state.
   InitGpio();  // Skipped for this example

// Step 3. Clear all interrupts and initialize PIE vector table:
// Disable CPU interrupts
   DINT;

// Initialize the PIE control registers to their default state.
// The default state is all PIE interrupts disabled and flags
// are cleared.
// This function is found in the f2802x_PieCtrl.c file.
   InitPieCtrl();

// Disable CPU interrupts and clear all CPU interrupt flags:
   IER = 0x0000;
   IFR = 0x0000;

// Initialize the PIE vector table with pointers to the shell Interrupt
// Service Routines (ISR).
// This will populate the entire table, even if the interrupt
// is not used in this example.  This is useful for debug purposes.
// The shell ISR routines are found in f2802x_DefaultIsr.c.
// This function is found in f2802x_PieVect.c.
   InitPieVectTable();

// Interrupts that are used in this example are re-mapped to
// ISR functions found within this file.
   EALLOW;  // This is needed to write to EALLOW protected register
   PieVectTable.ADCINT1 = &adc_isr;
//   PieVectTable.TINT0 = &cputimer0_isr;
   EDIS;    // This is needed to disable write to EALLOW protected registers

// Step 4. Initialize all the Device Peripherals:
// This function is found in f2802x_InitPeripherals.c
// InitPeripherals(); // Not required for this example
   ConfigCpuTimer(&CpuTimer0, 60, 2000000);
   CpuTimer0Regs.TCR.all = 0x4001; // Use write-only instruction to set TSS bit = 0
   InitAdc();  // For this example, init the ADC

// Step 5. User specific code, enable interrupts:

// Enable ADCINT1 & CPUTIMER0 in PIE
   PieCtrlRegs.PIEIER1.bit.INTx1 = 1;   // Enable INT 1.1 in the PIE
   PieCtrlRegs.PIEIER1.bit.INTx7 = 1;   // PIE Group 1 Vector INT1.7 --> CPU Timer 0

   IER |= M_INT1;                       // Enable CPU         Interrupt 1
   EINT;                                // Enable Global     interrupt INTM
   ERTM;                                // Enable Global     realtime interrupt DBGM

   LoopCount = 0;

// Configure ADC

//Note: Channel ADCINA4  will be double sampled to workaround the ADC 1st sample issue for rev0 silicon errata  

EALLOW;
AdcRegs.SOCPRICTL.bit.SOCPRIORITY = 0;  // SOC Priority is handled in round robin mode
AdcRegs.ADCCTL1.bit.INTPULSEPOS = 1;    //ADCINT1 trips after AdcResults latch
AdcRegs.INTSEL1N2.bit.INT1E     = 1;    //Enabled ADCINT1
AdcRegs.INTSEL1N2.bit.INT1CONT  = 0;    //Disable ADCINT1 Continuous mode
AdcRegs.INTSEL1N2.bit.INT1SEL   = 8;    //setup EOC8 to trigger ADCINT1 to fire
AdcRegs.ADCSOC8CTL.bit.CHSEL    = 7;    //set SOC8 channel select to ADCINA7
AdcRegs.ADCSOC8CTL.bit.TRIGSEL  = 1;    //set SOC8 start trigger on CPUTIMER0
AdcRegs.ADCSOC8CTL.bit.ACQPS    = 6;    //set SOC8 S/H Window to 7 ADC Clock Cycles, (6 ACQPS plus 1)

GpioCtrlRegs.GPBMUX1.bit.GPIO34 = 0;
GpioCtrlRegs.GPBDIR.bit.GPIO34 = 1;

EDIS;

// Wait for ADC interrupt
    while(1)
    {}

}
interrupt void  adc_isr(void)
{

  Voltage = AdcResult.ADCRESULT8;  //discard ADCRESULT0 as part of the workaround to the 1st sample errata for rev0
  GpioDataRegs.GPBTOGGLE.bit.GPIO34 = 1;
  AdcRegs.ADCINTFLGCLR.bit.ADCINT1 = 1;     //Clear ADCINT1 flag reinitialize for next SOC
  PieCtrlRegs.PIEACK.all = PIEACK_GROUP1;   // Acknowledge interrupt to PIE

  LoopCount++;
  if(LoopCount == 38000)
  {
      LoopCount = 0;
  }
  return;
}