TMS320F280023: 请问使用高精度PWM对PWM开关频率有最低要求吗？

在使用C:\ti\c2000\C2000Ware_3_04_00_00\device_support\f28002x\examples\hrpwm\hrpwm_ex2_prdupdown_sfo_v8.c例程时，PWM 5Mhz频率下通过示波器能清楚观测到周期边缘位置的变化，当PWM使用50Khz频率时，基本在示波器上看不到周期边缘有变化，请问是因为高精度PWM对于其频率有最低限度要求吗？如果不是的话为什么50Khz时观测不到变化

Green Deng：

据我所知应该没有这方面的限制，但是一般来说200KHz以下的用普通PWM，200KHz以上的用HRPWM。

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user6223461：

你好，感谢您的回复，现在情况是这样的，我在做一个等离子体电源的项目，PWM频率是50Khz，主要控制TBPRD寄存器来控制频率的变化，由于普通PWM的TBPRD寄存器未Uint16格式，因此我的频率只能50hz精度的调节，如果使用高精度PWM能够实现1hz精度的频率调节吗？还有之前问您的为什么在Demo中5Mhz使用高精度可以直接在示波器中观测到，而50Khz就看不见边缘有变化？

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Green Deng：

HRPWM是可以实现1Hz精度的频率调节的。至于为什么50KHz的时候没有变化，我可能需要咨询一下其他工程师讨论一下。你这边方便给出对应的配置和波形图吗

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user6223461：

程序就是C2000ware中的demo程序C:\ti\c2000\C2000Ware_3_04_00_00\device_support\f28002x\examples\hrpwm\hrpwm_ex2_prdupdown_sfo_v8.c

在不同时刻暂停，示波器上观测到的都是周期为20us的PWM波，边缘没有变化

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user6223461：

您好，请问有结果了吗？

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Green Deng：

你好，还没有，有结果了尽快回复你

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user6223461：

好的，感谢！

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Green Deng：

你好，看到你的程序中配置的TBCLK = SYSCLK，那在两种开关频率下配置的TBCLK都是一样的吗？都是F280023的默认配置频率？

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user6223461：

您好，两种开关频率下配置的TBCLK都是一样的，使用的280023默认的配置频率，所有配置只更改了HRPWM_Config()函数括号里的值

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Green Deng：

你好，目前还没有收到比较可靠的回复。不过我在例程主程序的开头注释中找到说明，这个例程需要在最大SYSCLKOUT下运行：

//! To load and run this example:
//! -# **!!IMPORTANT!!**
//! -# Run this example at maximum SYSCLKOUT
//! -# Activate Real time mode
//! -# Run the code
//! -# Watch ePWM A / B channel waveforms on a Oscilloscope
//! -# In the watch window:
//!Set the variable UpdateFine = 1to observe the ePWMxA & ePWMxB output
//!with HRPWM capabilities (default)
//!Observe the period/frequency of the waveform changes in fine MEP steps
//! -# In the watch window:
//!Change the variable UpdateFine to 0, to observe the
//!ePWMxA & ePWMxB output without HRPWM capabilities
//!Observe the period/frequency of the waveform changes in coarse
//!SYSCLKOUT cycle steps.

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user6223461：

您好，目前是运行在SYSCLKOUT下，程序默认配置了TBCLK = SYSCLK没有更改过，PWM的时钟是用的DSP的主频，能否和工程师确认下50Khz的PWM开关频率下能否使用高精度PWM？

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Green Deng：

你好，这边工程师回复，我怕翻译有误差，给你看一下原文：

It works at 50KHz. I just tested it on my setup. It is not easy to see it on the scope. You have to:

1. Trigger the scope on rising edge of the EPWM.

2. Zoom into the NEXT falling edge.

3. Change the TBPRDHR to see it changing.

50KHz works correctly.

//#############################################################################
//
// FILE:hrpwm_ex3_prdupdown_sfo.c
//
// TITLE:HRPWM Period Control.
//
//! \addtogroup driver_example_list
//! <h1>HRPWM Period Control</h1>
//!
//! This example modifies the MEP control registers to show edge displacement
//! for high-resolution period with ePWM in Up-Down count mode
//! due to the HRPWM control extension of the respective ePWM module.
//!
//! This example calls the following TI's MEP Scale Factor Optimizer (SFO)
//! software library V8 functions:
//!
//! \b int \b SFO(); \n
//! - updates MEP_ScaleFactor dynamically when HRPWM is in use
//! - updates HRMSTEP register (exists only in EPwm1Regs register space)
//!with MEP_ScaleFactor value
//! - returns 2 if error: MEP_ScaleFactor is greater than maximum value of 255
//!(Auto-conversion may not function properly under this condition)
//! - returns 1 when complete for the specified channel
//! - returns 0 if not complete for the specified channel
//!
//! This example is intended to explain the HRPWM capabilities. The code can be
//! optimized for code efficiency. Refer to TI's Digital power application
//! examples and TI Digital Power Supply software libraries for details.
//!
//! \b External \b Connections \n
//!- Monitor ePWM1/2/3/4 A/B pins on an oscilloscope.
//
//#############################################################################
// $TI Release: F28002x Support Library v3.04.00.00 $
// $Release Date: Fri Feb 12 18:58:34 IST 2021 $
// $Copyright:
// Copyright (C) 2021 Texas Instruments Incorporated - http://www.ti.com/
//
// Redistribution and use in source and binary forms, with or without// modification, are permitted provided that the following conditions// are met:
////Redistributions of source code must retain the above copyright//notice, this list of conditions and the following disclaimer.
////Redistributions in binary form must reproduce the above copyright
//notice, this list of conditions and the following disclaimer in the//documentation and/or other materials provided with the//distribution.
////Neither the name of Texas Instruments Incorporated nor the names of
//its contributors may be used to endorse or promote products derived
//from this software without specific prior written permission.
//// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// $
//#############################################################################
//
// Included Files
//
#include "driverlib.h"
#include "device.h"
#include "board.h"
#include "sfo_v8.h"//
// Defines
//
#define EPWM_TIMER_TBPRD1000UL
#define LAST_EPWM_INDEX_FOR_EXAMPLE5
#define MIN_HRPWM_PRD_PERCENT0.2//
// Globals
//float32_t periodFine = MIN_HRPWM_PRD_PERCENT;
uint16_t status;int MEP_ScaleFactor; // Global variable used by the SFO library// Result can be used for all HRPWM channels// This variable is also copied to HRMSTEP// register by SFO() function.volatile uint32_t ePWM[] ={0, myEPWM1_BASE, myEPWM2_BASE, myEPWM3_BASE, myEPWM4_BASE};
//
// Function Prototypes
//
void initHRPWM(uint32_t period);
void error(void);//
// Main
//
void main(void)
{uint16_t i = 0;//// Initialize device clock and peripherals//Device_init();//// Disable pin locks and enable internal pull ups.//Device_initGPIO();//// Initialize PIE and clear PIE registers. Disables CPU interrupts.//Interrupt_initModule();//// Initialize the PIE vector table with pointers to the shell Interrupt// Service Routines (ISR).//Interrupt_initVectorTable();//// Initialize EPWM GPIOs and change XBAR inputs from using GPIO0//Board_init();//// Calling SFO() updates the HRMSTEP register with calibrated MEP_ScaleFactor.// HRMSTEP must be populated with a scale factor value prior to enabling// high resolution period control.//while(status == SFO_INCOMPLETE){status = SFO();if(status == SFO_ERROR){error();// SFO function returns 2 if an error occurs & # of MEP}// steps/coarse step exceeds maximum of 255.}//// Disable sync(Freeze clock to PWM as well)//SysCtl_disablePeripheral(SYSCTL_PERIPH_CLK_TBCLKSYNC);initHRPWM(EPWM_TIMER_TBPRD);//// Enable sync and clock to PWM//SysCtl_enablePeripheral(SYSCTL_PERIPH_CLK_TBCLKSYNC);//// Enable Global Interrupt (INTM) and realtime interrupt (DBGM)//EINT;ERTM;for(;;){//// Sweep DutyFine////for(periodFine = MIN_HRPWM_PRD_PERCENT; periodFine < 0.9; periodFine += 0.01)//{DEVICE_DELAY_US(1000);
//for(i=1; i<LAST_EPWM_INDEX_FOR_EXAMPLE; i++)
//{
//float32_t count = ((EPWM_TIMER_TBPRD-1) << 8UL) + (float32_t)(periodFine * 256);
//uint32_t compCount = count;
//HRPWM_setTimeBasePeriod(ePWM[i], compCount);
//}//// Call the scale factor optimizer lib function SFO()// periodically to track for any change due to temp/voltage.// This function generates MEP_ScaleFactor by running the// MEP calibration module in the HRPWM logic. This scale// factor can be used for all HRPWM channels. The SFO()// function also updates the HRMSTEP register with the// scale factor value.//status = SFO(); // in background, MEP calibration module// continuously updates MEP_ScaleFactorif (status == SFO_ERROR){error();// SFO function returns 2 if an error occurs & #// of MEP steps/coarse step}// exceeds maximum of 255.//}}
}void initHRPWM(uint32_t period)
{uint16_t j;//// ePWM channel register configuration with HRPWM//for (j=1;j<LAST_EPWM_INDEX_FOR_EXAMPLE;j++){EPWM_setEmulationMode(ePWM[j], EPWM_EMULATION_FREE_RUN);//// Set-up TBCLK//EPWM_setPeriodLoadMode(ePWM[j], EPWM_PERIOD_SHADOW_LOAD);EPWM_setTimeBasePeriod(ePWM[j], period-1);EPWM_setPhaseShift(ePWM[j], 0U);EPWM_setTimeBaseCounter(ePWM[j], 0U);//// set duty 50% initially//HRPWM_setCounterCompareValue(ePWM[j], HRPWM_COUNTER_COMPARE_A, (period/2 << 8));HRPWM_setCounterCompareValue(ePWM[j], HRPWM_COUNTER_COMPARE_B, (period/2 << 8));//// Set up counter mode//EPWM_setTimeBaseCounterMode(ePWM[j], EPWM_COUNTER_MODE_UP_DOWN);EPWM_disablePhaseShiftLoad(ePWM[j]);EPWM_setClockPrescaler(ePWM[j],EPWM_CLOCK_DIVIDER_1,EPWM_HSCLOCK_DIVIDER_1);//// Set up shadowing//EPWM_setCounterCompareShadowLoadMode(ePWM[j],EPWM_COUNTER_COMPARE_A,EPWM_COMP_LOAD_ON_CNTR_ZERO);EPWM_setCounterCompareShadowLoadMode(ePWM[j],EPWM_COUNTER_COMPARE_B,EPWM_COMP_LOAD_ON_CNTR_ZERO);//// Set actions//EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_A,EPWM_AQ_OUTPUT_HIGH,EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_B,EPWM_AQ_OUTPUT_HIGH,EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_A,EPWM_AQ_OUTPUT_LOW,EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_B,EPWM_AQ_OUTPUT_LOW,EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);HRPWM_setMEPEdgeSelect(ePWM[j], HRPWM_CHANNEL_A, HRPWM_MEP_CTRL_RISING_AND_FALLING_EDGE);HRPWM_setMEPControlMode(ePWM[j], HRPWM_CHANNEL_A, HRPWM_MEP_DUTY_PERIOD_CTRL);HRPWM_setCounterCompareShadowLoadEvent(ePWM[j], HRPWM_CHANNEL_A, HRPWM_LOAD_ON_CNTR_ZERO_PERIOD);HRPWM_setMEPEdgeSelect(ePWM[j], HRPWM_CHANNEL_B, HRPWM_MEP_CTRL_RISING_AND_FALLING_EDGE);HRPWM_setMEPControlMode(ePWM[j], HRPWM_CHANNEL_B, HRPWM_MEP_DUTY_PERIOD_CTRL);HRPWM_setCounterCompareShadowLoadEvent(ePWM[j], HRPWM_CHANNEL_B, HRPWM_LOAD_ON_CNTR_ZERO_PERIOD);HRPWM_enableAutoConversion(ePWM[j]);//// Turn on high-resolution period control.//HRPWM_enablePeriodControl(ePWM[j]);HRPWM_enablePhaseShiftLoad(ePWM[j]);EPWM_forceSyncPulse(ePWM[j]);}}//
// error - Halt debugger when called
//
void error (void)
{ESTOP0;// Stop here and handle error
}

Again trigger on rising edge, zoom into the following falling edge.

Change the TBPRDHR from 0 tp 0xE000 and see the shift.

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user6223461：

好的明白了，非常感谢您和其他工程师，谢谢！