Mathematical operations on DSP

Hi Fasil,

Check this thread: e2e.ti.com/.../317928

Regards,
Gautam

Hi Fasil,

May this link can help you: www.electronics-tutorials.ws/.../rms-voltage.html

Regards,
Phien Nguyen

My requirement is that i need to find rms of a signal 0-3V which I have given as input to ADC. It has sampled and stored in a buffer register. The program I used is ADCSOC with slight variations. Now what should I do to find its rms.?? This is f28335 and using CCS v3.3. Is it possible to view the answer in CCS?

What is the significance of this command:
va_ADC = AdcRegs.ADCRESULT0 >>4;

This will give you the digital value.
AdcRegs.ADCRESULT0 >>4 will give you a 12bit digital value ie 0V represents 0 and 3V -> 4095

is it possible to display rms value in ccs?

how to display value in ccs?

I edited the interrupt function of my program(ADCSOC) , for finding rms. Please tell me the mistakes in this:

interrupt void adc_isr(void)
{
int sum=0;
int rms=0;
int va_ADC;

Voltage1[ConversionCount] = AdcRegs.ADCRESULT0 >>4;
va_ADC = AdcRegs.ADCRESULT0 >>4;
sum = sum + va_ADC*va_ADC;

// If 40 conversions have been logged, start over
if(ConversionCount == 1999)
{
ConversionCount = 0;
}
else ConversionCount++;

// Reinitialize for next ADC sequence
AdcRegs.ADCTRL2.bit.RST_SEQ1 = 1; // Reset SEQ1
AdcRegs.ADCST.bit.INT_SEQ1_CLR = 1; // Clear INT SEQ1 bit
PieCtrlRegs.PIEACK.all = PIEACK_GROUP1; // Acknowledge interrupt to PIE

return;
rms = sqrt(sum/2000);
}

Can you please figure out the mistake:-

#include "DSP28x_Project.h" // Device Headerfile and Examples Include File

// Prototype statements for functions found within this file.
interrupt void adc_isr(void);

// Global variables used in this example:
Uint16 LoopCount;
Uint16 ConversionCount;
Uint16 Voltage1[2000];

Uint16 sum=0;
Uint16 rms=0;
Uint16 va_ADC;
Uint16 va;
main()
{

// Step 1. Initialize System Control:
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the DSP2833x_SysCtrl.c file.
InitSysCtrl();

EALLOW;
#if (CPU_FRQ_150MHZ) // Default - 150 MHz SYSCLKOUT
#define ADC_MODCLK 0x3 // HSPCLK = SYSCLKOUT/2*ADC_MODCLK2 = 150/(2*3) = 25.0 MHz
#endif
#if (CPU_FRQ_100MHZ)
#define ADC_MODCLK 0x2 // HSPCLK = SYSCLKOUT/2*ADC_MODCLK2 = 100/(2*2) = 25.0 MHz
#endif
EDIS;

// Step 2. Initialize GPIO:
// This example function is found in the DSP2833x_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 DSP2833x_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 DSP2833x_DefaultIsr.c.
// This function is found in DSP2833x_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.ADCINT = &adc_isr;
EDIS; // This is needed to disable write to EALLOW protected registers

// Step 4. Initialize all the Device Peripherals:
// This function is found in DSP2833x_InitPeripherals.c
// InitPeripherals(); // Not required for this example
InitAdc(); // For this example, init the ADC
// For this example, only initialize the ePWM


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

// Enable ADCINT in PIE
PieCtrlRegs.PIEIER1.bit.INTx6 = 1;
IER |= M_INT1; // Enable CPU Interrupt 1
EINT; // Enable Global interrupt INTM
ERTM; // Enable Global realtime interrupt DBGM

LoopCount = 0;
ConversionCount = 0;


// Enable global Interrupts and higher priority real-time debug events:
EINT; // Enable Global interrupt INTM
ERTM; // Enable Global realtime interrupt DBGM

// Configure ADC
AdcRegs.ADCMAXCONV.all = 0x0000; // Setup 2 conv's on SEQ1
AdcRegs.ADCCHSELSEQ1.bit.CONV00 = 0x3; // Setup ADCINA3 as 1st SEQ1 conv.

AdcRegs.ADCTRL2.bit.EPWM_SOCA_SEQ1 = 1;// Enable SOCA from ePWM to start SEQ1
AdcRegs.ADCTRL2.bit.INT_ENA_SEQ1 = 1; // Enable SEQ1 interrupt (every EOS)

// Assumes ePWM1 clock is already enabled in InitSysCtrl();
EPwm1Regs.ETSEL.bit.SOCAEN = 1; // Enable SOC on A group
EPwm1Regs.ETSEL.bit.SOCASEL = 4; // Select SOC from from CPMA on upcount
EPwm1Regs.ETPS.bit.SOCAPRD = 1; // Generate pulse on 1st event
EPwm1Regs.CMPA.half.CMPA = 0x0080; // Set compare A value
EPwm1Regs.TBPRD = 400; // Set period for ePWM1
EPwm1Regs.TBCTL.bit.CTRMODE = 0; // count up and start
EPwm1Regs.TBCTL.bit.HSPCLKDIV = TB_DIV2; // Clock ratio to SYSCLKOUT
EPwm1Regs.TBCTL.bit.CLKDIV = TB_DIV2;
// Wait for ADC interrupt
for(;;)
{
LoopCount++;
}
}
interrupt void adc_isr(void)
{


Voltage1[ConversionCount] = AdcRegs.ADCRESULT0 >>4;
va_ADC = AdcRegs.ADCRESULT0 >>4;
va = (va_ADC*3)/4096;
sum = sum + (va*va);

// If 40 conversions have been logged, start over
if(ConversionCount == 1999)
{
ConversionCount = 0;
}
else ConversionCount++;
rms = sqrt(sum/2000);
// Reinitialize for next ADC sequence
AdcRegs.ADCTRL2.bit.RST_SEQ1 = 1; // Reset SEQ1
AdcRegs.ADCST.bit.INT_SEQ1_CLR = 1; // Clear INT SEQ1 bit
PieCtrlRegs.PIEACK.all = PIEACK_GROUP1; // Acknowledge interrupt to PIE

return;

}

What is the issue you're facing with this code? With the code you need to describe the issue too.

I am giving a sine wave with maximum voltage 3 and offset 1.5V. This program doesn't give me the correct rms.

Fasil Mohamed said:

This program doesn't give me the correct rms.

What is the deviation? Also, did you check this thread thoroughly?

I found the mistake. thanks

Great! Please close this thread by verifying the answer.

Goodluck & Regards,
Gautam

Fasil,

int sum=0;
sum = sum + va_ADC*va_ADC;
rms = sqrt(sum/2000);

I do not know which device your are using but I guess your variable 'sum' may not big enough to calculate correctly. It will get an overflow sooner or later. And sum is declared only locally, this does not make much sense...

Best regards,

Karlheinz