MSP432E401Y: PWM外设的频率问题

Technical Reference似乎表示了不同的PWM Generator可以采用不同的波形频率。

然而我在使用TI-drivers时无法使不同发生器的PWM采用不同频率。我该如何解决？

此外，MSP432E4系列的产品的timer的PWM_MODE产生的波形是否有占空比为50%的限制？

Susan Yang：

您是否有参考TI例程：

simplelink_msp432e4_sdk_4_20_00_12\examples\nortos\MSP_EXP432E401Y\driverlib\pwm_genx_syncgenerators 

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林畅：

你好 这是driverlib的例程 然而在TI drivers在PWM_open()内使用不同的频率或周期可能会出现问题。

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Susan Yang：

林畅 说：可能会出现问题

请问能否说一下具体是什么问题？是会在编译时报错还是可以编译成功但使用时功能不正常？

若是可以，能否给出完整代码，我在开发板上测试一下

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林畅：

可以过编译。然而PWM_open()的返回值是NULL.具体情况是在PWMMSP432E4.c里initHw()中此处返回的错误导致。我这里尽管使用了不同generator的引脚，可是只要频率不同就无法打开PWM。我该如何向你发送代码？

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Susan Yang：

林畅 说：我该如何向你发送代码？

您应该会收到我发给您的消息吧，直接回复即可。使用附件压缩包的方式上传，谢谢

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Susan Yang：

抱歉，我这边找了一下，没有MSP432E的板子，所以我是使用MSP432P系列来测试的

代码如下，不建议您在循环内打开PWM，即

/*** – custom variables end – ***/ for(int i=0;i<CONFIG_PWM_COUNT;i++){ pwmHandle[i] = PWM_open(i, pwmParams+i); if(pwmHandle[i]==NULL){ //error: PWM did not open //there had better a UART output while(1); }

而是尝试逐个打开

/** Copyright (c) 2015-2019, Texas Instruments Incorporated* All rights reserved.** 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.*//**======== pwmled2.c ========*/
/* For usleep() */
#include <unistd.h>
#include <stddef.h>/* Driver Header files */
#include <ti/drivers/PWM.h>/* Driver configuration */
#include "ti_drivers_config.h"/**======== mainThread ========*Task periodically increments the PWM duty for the on board LED.*/
void *mainThread(void *arg0)
{/* Period and duty in microseconds */uint16_tpwmPeriod = 3000;uint16_tduty = 0;uint16_tdutyInc = 100;/* Sleep time in microseconds */uint32_ttime = 50000;PWM_Handle pwm1 = NULL;PWM_Handle pwm2 = NULL;PWM_Params params;/* Call driver init functions. */PWM_init();PWM_Params_init(&params);params.dutyUnits = PWM_DUTY_US;params.dutyValue = 0;params.periodUnits = PWM_PERIOD_US;params.periodValue = pwmPeriod;pwm1 = PWM_open(CONFIG_PWM_0, &params);if (pwm1 == NULL) {/* CONFIG_PWM_0 did not open */while (1);}PWM_start(pwm1);pwm2 = PWM_open(CONFIG_PWM_1, &params);if (pwm2 == NULL) {/* CONFIG_PWM_0 did not open */while (1);}PWM_start(pwm2);/* Loop forever incrementing the PWM duty */while (1) {PWM_setDuty(pwm1, duty);PWM_setDuty(pwm2, duty);duty = (duty + dutyInc);if (duty == pwmPeriod || (!duty)) {dutyInc = - dutyInc;}usleep(time);}
}

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林畅：

能讲一下原因吗

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Susan Yang：

您可以看一下下面链接的 

MPS432 PWM Driver Configuration

http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/SIMPLELINK_MSP432_SDK/1.20.00.45/exports/docs/tidrivers/doxygen/html/_p_w_m_timer_m_s_p432_8h.html 

以及说明：

Only one PWM index can be used at a time; calling PWM_open() a second time with the same index previously passed to PWM_open() will result in an error. You can, though, re-use the index if the instance is closed via PWM_close(). In the example code, Board_PWM0 is passed to PWM_open(). This macro is defined in the example's Board.h file.

另外我之前附上的代码是MSP432P401R系列的例程

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林畅：

你好，我虽然使用了循环打开PWM，但是我并没有使用同样的index，而是利用了循环变量i“PWM_open(i,params+i)”

此外，MSP432P4和E4型号名字相似，但是PWM实现外设不同，差别较大，还麻烦您帮我再问一问，以解我心头之困，谢谢

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Susan Yang：

谢谢您的反馈，我之后会咨询下同事后给您回复