Problem with too much ADC gain

#include <stdio.h>

#include "DSP28x_Project.h"

#define N_AVG      10000  // Number of values to average
#define BUF_SIZE   5  // Sample buffer size

static void init_adc_custom_cal(void);
static void measure(void);



void main()
{

	InitSysCtrl();// DSP2833x_SysCtrl.c file; PLL, Watchdog, Peripheral Clocks
	
	DINT;// Disable CPU interrupts

	InitPieCtrl();// DSP2833x_PieCtrl.c file

	IER = 0x0000;// Disable CPU interrupts
	IFR = 0x0000;// Clear all CPU interrupts

	InitPieVectTable();// DSP2833x_PieVect.c file

	//ADC setup for this example
#if 0
	init_adc_custom_cal(); /* Custom init of offset and gain */
#else
	InitAdc(); /* Standard init of offset and gain */
#endif

	/* ADC clock frequency:
	 *
	 * High-speed peripheral clock (HSPCLK) frequency =
     *	 	System clock frequency / SysCtrlRegs.HISPCP[3:0]
	 * Note that only the ADC uses the high-speed peripheral clock.
	 *
	 *
	 * ADC clock frequency = HSPCLK / (2 * ADCCLKPS[3:0] * (CPS + 1))
	 * unless ADCCLKPS[3:0] = 0. Then
	 * ADC clock frequency = HSPCLK / (1 * (CPS + 1))
	 *
	 * Acquisition window size is the corresponding ADC clock period
	 * times (ACQ_PS + 1)
	 */

	AdcRegs.ADCTRL1.bit.SEQ_CASC = 1;// Cascaded mode
	AdcRegs.ADCTRL3.bit.SMODE_SEL = 0;// Sequential sampling mode 
	AdcRegs.ADCMAXCONV.bit.MAX_CONV1 = 3;
	AdcRegs.ADCCHSELSEQ1.bit.CONV00 = 0;// ADC input channel: ADCINA0
	AdcRegs.ADCCHSELSEQ1.bit.CONV01 = 1;// ADC input channel: ADCINA0
	AdcRegs.ADCCHSELSEQ1.bit.CONV02 = 2;// ADC input channel: ADCINA0
	AdcRegs.ADCCHSELSEQ1.bit.CONV03 = 3;// ADC input channel: ADCINA0
	AdcRegs.ADCTRL1.bit.CONT_RUN = 1;//  Continuous conversion mode
	AdcRegs.ADCTRL2.all = 0x2000;// Start SEQ1; INT_SEQ1 is set at the end of every SEQ1 sequence

	/* Use ADC to measure voltage */
	measure();
	return;
}    



/* Measure ADC signals with different parameters */
#define N_ITER_PER_TEST	5
static void measure(void)
{
	Uint32 msmt0, msmt1, msmt2, msmt3, msmt_ave;
	Uint16 cps; /* timing */
	int rc_print = 0; /* Init print return code */

	/* Print header */
	rc_print = fprintf(stdout,
		"Average over %lu samples,,,,,,,,,,\n"
		"CPS,ADCCLKPS,ACQ_PS,ADC_SAMP_FREQ (MHz),ACQ_PERIOD (us),ITER,CH0,CH1,CH2,CH3,AVE\n",
		(Uint32) N_AVG);

	/* Loops over meaasurement parameters */
	for (cps = 0; cps <= 1; cps++) { /* Vary CPS between 0 and 1 */
		Uint16 adcclkps;
		AdcRegs.ADCTRL1.bit.CPS = cps;
		for (adcclkps = 0; adcclkps <= 15; adcclkps++) {
			Uint16 acq_ps;
			AdcRegs.ADCTRL3.bit.ADCCLKPS = adcclkps;
			/* Note: starting at 1 because program hung at
			 * adcclkps=1 acq_ps = 0 */
			for (acq_ps = 1; acq_ps <= 15; acq_ps++) {
				Uint16 iter;
				float freq_temp = adcclkps == 0 ?
						75.0f : 75.0f / (2 * adcclkps);
				float freq_samp_mhz = cps == 0 ?
						freq_temp : freq_temp / 2;
				float sample_hold_time_us = (1 + acq_ps) / freq_samp_mhz;
				AdcRegs.ADCTRL1.bit.ACQ_PS = acq_ps; /* acquisition window */
				
				for (iter = 1; iter <= N_ITER_PER_TEST; iter++) {
					Uint16 i;

					msmt0 = msmt1 = msmt2 = msmt3 = 0; /* init accum to 0 */

					for (i = 0; i < N_AVG; i++) {
						/* Wait for interrupt */
						while (AdcRegs.ADCST.bit.INT_SEQ1== 0) {}

						AdcRegs.ADCST.bit.INT_SEQ1_CLR = 1;

						msmt0 += AdcRegs.ADCRESULT0 >> 4;
						msmt1 += AdcRegs.ADCRESULT1 >> 4;
						msmt2 += AdcRegs.ADCRESULT2 >> 4;
						msmt3 += AdcRegs.ADCRESULT3 >> 4;
					}

					/* Overall average */
					msmt_ave = (msmt0 + msmt1 + msmt2 + msmt3) /
							((Uint32) 4 *  (Uint32) N_AVG); 

					/* Individual results */
					msmt0 /= N_AVG;
					msmt1 /= N_AVG;
					msmt2 /= N_AVG;
					msmt3 /= N_AVG;

					/* Output results */ 
					rc_print |=  fprintf(stdout,
							"%u,%u,%u,%G,%G,%u,%lu,%lu,%lu,%lu,%lu\n",
							cps, adcclkps, acq_ps,
							freq_samp_mhz, sample_hold_time_us,
							iter, msmt0, msmt1, msmt2, msmt3, msmt_ave);
				} /* end of loop over iterations */
			} /* end of loop over acq_ps */
		} /* end of loop over adcclkps */
	} /* end of loop over ps */

	/* Test for print error */
	if (rc_print < 0) {
		(void) fprintf(stderr, "Unable to print data to output file.\n");
	}

	return;
} /* end of function measure */



static void init_adc_custom_cal(void)
{

    extern void DSP28x_usDelay(Uint32 Count);


	// *IMPORTANT*
	// The ADC_cal function, which  copies the ADC calibration values from TI reserved
	// OTP into the ADCREFSEL and ADCOFFTRIM registers, occurs automatically in the
	// Boot ROM. If the boot ROM code is bypassed during the debug process, the
	// following function MUST be called for the ADC to function according
	// to specification. The clocks to the ADC MUST be enabled before calling this
	// function.
	// See the device data manual and/or the ADC Reference
	// Manual for more information.

    EALLOW;
	SysCtrlRegs.PCLKCR0.bit.ADCENCLK = 1;

	/* Calibration */
#if 1
	AdcRegs.ADCOFFTRIM.all = 505; /* 0:8, 505 from factory */
//	AdcRegs.ADCREFSEL.all = 7490; /* 0:13, 7460 from factory */
	AdcRegs.ADCREFSEL.all = 0x0000; /* 0:13, 7460 from factory */
#else
	asm("  MOVW  DP,   #0x711C >> 6");
	asm("  MOV   @28,  #0x7460");
	asm("  MOV   @29,  #0x505");
#endif

	EDIS;


    // To powerup the ADC the ADCENCLK bit should be set first to enable
    // clocks, followed by powering up the bandgap, reference circuitry, and ADC core.
    // Before the first conversion is performed a 5ms delay must be observed
	// after power up to give all analog circuits time to power up and settle

    // Please note that for the delay function below to operate correctly the
	// CPU_RATE define statement in the DSP2833x_Examples.h file must
	// contain the correct CPU clock period in nanoseconds.

    AdcRegs.ADCTRL3.all = 0x00E0;  // Power up bandgap/reference/ADC circuits
    DELAY_US(5000L);         // Delay before converting ADC channels

	return;
} /* end of function init_adc_custom_cal */