TMS320F28335利用ePWM改变ADC采样频率(双通道)示例代码

2020-05-31 17:41:09

TMS320F28335 想实现设定ADC采样频率，通过设置 ADC_CKPS 和 ADC_SHCLK 分频系数是可以在一定范围内改变ADC采样频率的，但是只调节分频系数时，ADC采样频率最低只能到十几KHz： 28335 ADC 对100Hz方波采样，于是问题变得复杂了一些。

参考了有相同需求的帖子：28335的ADC采样频率如何设置？ 、DSP28335中如何设置ADC采样的频率？

得出结论：若想把ADC采样频率降低到一定水平（如1000Hz、2000Hz等），仅改变ADC分频系数是不够的，还需利用ePWM来生成ADC的启停信号，使其作为ADC的开关，释放启停信号来控制ADC，进而改变ADC的采样频率可调，而ePWM的频率就是ADC启停频率，

于是我们现在关心ePWM的频率/周期设置：

ePWM的寄存器主要有7个，我们这里重点关注：时基周期寄存器TBPRD和时基计数器模式：

于是，决定Tpwm的变量有计算公式、TBPRD和TBCLK：

(1).计算公式：不同计数模式的计算公式不同，从图中看出：

　　在增减计数模式下，Tpwm = (TBPRD+1) x TBCLK ;

　　在递增和递减计数模式下，Tpwm = 2 x TBPRD x TBCLK ;

(2).TBCLK = SYSCLKOUT / ( (2*HSPCLKDIV) * (2^CLKDIV) );

TBCLK由 SYSCLKOUT、HSPCLKDIV和CLKDIV决定，这里28335的SYSCLKOUT默认150MHz，查表后得知：代码中 CLKDIV = n ，公式中变为：CLKDIV = 2^n ；在程序中 HSPCLKDIV = n，公式中 HSPCLKDIV = 2n ;

(3).TBPRD：按照公式（不同计数模式的Tpwm公式不同）计算得出数，手动填入，例如要把PWM的频率、（即ADC的采样频率）设置为2000Hz：

// Set Period for EPWM1  
// up-and-down count mode:
// Tpwm = 2*(1/TBCLK)*TBPRD;
 
// up-count mode or down-count mode:( use this mode here )
// Tpwm = (1/TBCLK)*(1+TBPRD);    
    EPwm1Regs.TBPRD = (12500-1); // max = 65536
 // Setup  T(PWM1)=(1/TBCLK)*(1+TBPRD)=(1/25000000)*(1+12500-1)=0.0005s ,F(PWM1) = 1/T(PWM1) = 1/0.0005s = 2000Hz

完整的可用ADC.c代码如下：

#include "DSP2833x_Device.h"     // DSP2833x Headerfile Include File
#include "DSP2833x_Examples.h"   // DSP2833x Examples Include File
#include "math.h"
#include "DSP2833x_Project.h"
#include "DSP2833x_EPwm.h"
#include "DSP2833x_EPwm_defines.h"
// lower sample rate to 2KHz using ePWM interrupt
// as well as turn on 2 channels 

// Determine when the shift to right justify the data takes place
// Only one of these should be defined as 1.
// The other two should be defined as 0.
#define POST_SHIFT   0  // Shift results after the entire sample table is full
#define INLINE_SHIFT 1  // Shift results as the data is taken from the results regsiter
#define NO_SHIFT     0  // Do not shift the results

#define BUF_SIZE   512  // Sample buffer size

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

    // Global variables used in this example:
    Uint16 LoopCount_1;
    Uint16 LoopCount_2;
    Uint16 ConversionCount;

    Uint16 SampleTable_1[BUF_SIZE]={0};
    Uint16 SampleTable_2[BUF_SIZE]={0};


    main()
    {

    // 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;
    // 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();

    EALLOW;
    SysCtrlRegs.HISPCP.all = ADC_MODCLK;                       // set ADC CLOCK ,HSPCLK = SYSCLKOUT/ADC_MODCLK
    EDIS;

    // 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

    InitAdc();                                                                                     // For this example, init the ADC

    // 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_1 = 0;
    LoopCount_2 = 0;
    ConversionCount = 0;

    // Configure ADC
    ///////////////////////设置最大通道数：2/////////////////////////////
    AdcRegs.ADCMAXCONV.all = 0x0001;                                         // Setup 2 conv's on SEQ1
    AdcRegs.ADCCHSELSEQ1.bit.CONV00 = 0x0;                             // Setup ADCINA3 as 1st SEQ1 conv.
    AdcRegs.ADCCHSELSEQ1.bit.CONV01 = 0x1;                             // Setup ADCINA2 as 2nd 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.TBCTL.bit.CTRMODE = 0;                                         // 0 -- count up and start

///////////////配置ePWM中断频率，即设置ADC采样频率////////////////    
// High Speed Time-base Clock Prescale Bits,These bits determine part of the time-base clock prescale
// SYSCLKOUT = 150MHz    
// TBCLK = SYSCLKOUT / ( (2*HSPCLKDIV) * (2^CLKDIV) )=150MHz/(2*3*1)=25MHz      
   EPwm1Regs.TBCTL.bit.HSPCLKDIV =0x03; 
   EPwm1Regs.TBCTL.bit.CLKDIV = 0x00;

// Set Period for EPWM1  
// up-and-down count mode:
// Tpwm = 2*(1/TBCLK)*TBPRD;
    
// up-count mode or down-count mode:( use this mode here )
// Tpwm = (1/TBCLK)*(1+TBPRD);    
   EPwm1Regs.TBPRD = (12500-1);                                            // max = 65536
// Setup  T(PWM1)=(1/TBCLK)*(1+TBPRD)=(1/25000000)*(1+12500-1)=0.0005s ,F(PWM1) = 1/T(PWM1) = 1/0.0005s = 2000Hz
//////////////////////////////////////////////////////////////////////

// Wait for ADC interrupt
while(1)
{
    LoopCount_1++;
}

}


interrupt void adc_isr(void)
{
    LoopCount_2++;
    if(LoopCount_2 == 10000)
    {
    LoopCount_2 = 0;
    }
    SampleTable_1[ConversionCount] = AdcRegs.ADCRESULT0 >>4;
    SampleTable_2[ConversionCount] = AdcRegs.ADCRESULT1 >>4;

    // If BUF_SIZE(512) conversions have been logged, start over
    if(ConversionCount == BUF_SIZE)
    {
    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;
} 

参考：

DSP EPWM学习笔记1 - EPWM定时中断

利用28335的epwm产生spwm波的总结

F28335 使用EPWM控制ADC采样 能进ADC中断，但ADCRESULTx结果不对

F28335 ADC多通道连续采样 代码+注释