DSP28069 eCAP 模块捕获方波

注意：在捕获方波时，方波电压范围要在0~3.3V，电压高于3.3V会烧坏芯片，低于0V会捕获不到。

       捕获原理：通过设置eCAP模块的寄存器，对引脚电平进行监测，分别记录下方波上升沿，下降沿的时间，在进行计算，得出所捕获的频率、占空比。

       连续/单次模式：2位Mod4计数器对相应的边沿捕获事件递增计数（CEVT1~4）；Mod4计数器循环计数（0→1→2→3→0），直至停止工作。

        在单次模式下，eCAP模块等待N（1~4）个捕获事件的发生，N值为停止寄存器的值。达到N值后，Mod4计数器和CAP寄存器的值将被冻结。如果向CAP控制寄存器ECCTL2中的单次加载REARM位写1后，Mod4计数器恢复作用，同时如果将ECCTL1中CAPLDEN置1，那么CAP1~4会再次加载新值。

        在连续模式下，Mod4计数器持续工作（0→1→2→3→0），捕获值在一个环形缓冲里按顺序不断写入有CAP1~4。

         CAP寄存器配置程序：

void InitECapture()
{
   ECap1Regs.ECEINT.all = 0x0000;             // Disable all capture interrupts
   ECap1Regs.ECCLR.all = 0xFFFF;              // Clear all CAP interrupt flags
   ECap1Regs.ECCTL1.bit.CAPLDEN = 0;          // Disable CAP1-CAP4 register loads
   ECap1Regs.ECCTL2.bit.TSCTRSTOP = 0;        // Make sure the counter is stopped

   // Configure peripheral registers
   ECap1Regs.ECCTL2.bit.CONT_ONESHT = 0;      // 0:One-shot mode   1:Continuous mode
   ECap1Regs.ECCTL2.bit.STOP_WRAP = 3;        // Stop at 4 events

   ECap1Regs.ECCTL1.bit.CAP1POL = 1;          // Falling edge
   ECap1Regs.ECCTL1.bit.CAP2POL = 0;          // Rising edge
   ECap1Regs.ECCTL1.bit.CAP3POL = 1;          // Falling edge
   ECap1Regs.ECCTL1.bit.CAP4POL = 0;          // Rising edge
   ECap1Regs.ECCTL1.bit.CTRRST1 = 0;          // Difference operation
   ECap1Regs.ECCTL1.bit.CTRRST2 = 0;          // Difference operation
   ECap1Regs.ECCTL1.bit.CTRRST3 = 0;          // Difference operation
   ECap1Regs.ECCTL1.bit.CTRRST4 = 0;          // Difference operation

   ECap1Regs.ECCTL2.bit.SYNCI_EN = 1;         // Enable sync in
   ECap1Regs.ECCTL2.bit.SYNCO_SEL = 0;        // Pass through
   ECap1Regs.ECCTL1.bit.CAPLDEN = 1;          // Enable capture units

   ECap1Regs.ECCTL2.bit.TSCTRSTOP = 1;        // Start Counter
   ECap1Regs.ECCTL2.bit.REARM = 1;            // arm one-shot
   ECap1Regs.ECCTL1.bit.CAPLDEN = 1;          // Enable CAP1-CAP4 register loads
   ECap1Regs.ECEINT.bit.CEVT4 = 1;            // 4 events = interrupt

}

        配置各个寄存器含义：

ECCTL1
CAPLDEN	在捕获事件中使能CAP1~4寄存器的加载； 0：禁止加载；1：使能加载
CAPxPOL	捕捉沿选择 0：上升沿捕捉；1：下降沿捕捉
CTRRSTx	CAPx事件中重置计数器 0：不重置；1：重置
CEVTx	1：在第x个捕捉事件中产生中断
ECCTL2
TSCTRSTOP	计数器停止位控制； 0：停止；1：计数
CON_ONESHT	模式选择； 0：连续模式；1：单次模式
STOP_WRAP	单次/连续模式下的停止值，CAP1-0/CAP2-1/CAP3-2/CAP4-3 单次模式下：在CAPx的捕捉事件发生后产生停止信号 连续模式下：在CAPx的捕捉事件发生后计数器正常运行

        当程序运行四个事件后发生中断，在中断中计算捕获的频率、占空比，程序如下：

__interrupt void ecap1_isr(void)
{
   // Cap input is syc'ed to SYSCLKOUT so there may be
   // a +/- 1 cycle variation
   t1 = ECap1Regs.CAP1;
   t2 = ECap1Regs.CAP2;
   t3 = ECap1Regs.CAP3;
   t4 = ECap1Regs.CAP4;

   T1 = t4 - t2;  // period time 
   T2 = t3 - t2;  // duty time

   Frequency = (90000000 / T1); //frequency

   Duty = 100 * T2/T1; // duty 

   ECap1Regs.ECCLR.bit.CEVT4 = 1;
   ECap1Regs.ECCLR.bit.INT = 1;
   ECap1Regs.ECCTL2.bit.REARM = 1;

   // Acknowledge this interrupt to receive more interrupts from group 4
   PieCtrlRegs.PIEACK.all = PIEACK_GROUP4;
}

        主程序如下：

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

// Prototype statements for functions found within this file.
__interrupt void ecap1_isr(void);
void InitECapture(void);

// Global variables used in this example
Uint32 t1, t2, t3, t4;
float32 T1, T2;
float32 Frequency, Duty;


void main(void)
{

// Step 1. Initialize System Control:
// PLL, WatchDog, enable Peripheral Clocks
// This example function is found in the F2806x_SysCtrl.c file.
   InitSysCtrl();

// Step 2. Initalize GPIO:
// This example function is found in the F2806x_Gpio.c file and
// illustrates how to set the GPIO to it's default state.
// InitGpio();  // Skipped for this example

   InitECap1Gpio();

// 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 F2806x_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 F2806x_DefaultIsr.c.
// This function is found in F2806x_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 registers
   PieVectTable.ECAP1_INT = &ecap1_isr;
   EDIS;    // This is needed to disable write to EALLOW protected registers

// Step 4. Initialize all the Device Peripherals:
// This function is found in F2806x_InitPeripherals.c
// InitPeripherals();  // Not required for this example
   InitECapture();

// Step 5. User specific code, enable interrupts:
   T1 = 0;
   T2 = 0;
   t1 = 0;
   t2 = 0;
   t3 = 0;
   t4 = 0;
   Frequency = 0;
   Duty = 0;
// Enable CPU INT4 which is connected to ECAP1-4 INT:
   IER |= M_INT4;

// Enable eCAP INTn in the PIE: Group 3 interrupt 1-6
   PieCtrlRegs.PIEIER4.bit.INTx1 = 1;

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

// Step 6. IDLE loop. Just sit and loop forever (optional):
   for(;;)
   {
      __asm("          NOP");
   }

}

捕获到频率产生误差，可在中断程序计算中进行修正。