Timer_A 输出 PWM的问题
在官方例程中给出的是一种直接操作寄存器的方式启动的，这让我们这些刚刚接触MSP432这种嵌入式芯片的来说是很难看懂的，然而PWM的输出是可以重新映射到其它端口输出的，例程中又掺杂了PMAP GPIO端口的映射，这更使得学习无从下手。
通过寄存器操作的方式输出PWM波形
TIMER_A0->CCR[0] = PWM_PERIOD;
TIMER_A0->CCTL[1] = TIMER_A_CCTLN_OUTMOD_7; // CCR1 Reset/set
TIMER_A0->CCR[1] = PWM_PERIOD * (55 / 100.0); // CCR1 PWM duty cycle
TIMER_A0->CTL = TIMER_A_CTL_SSEL__SMCLK // 使用SMCLK时钟源
| TIMER_A_CTL_MC__UP
| TIMER_A_CTL_CLR; // SMCLK, up mode, clear TAR
引用msp432p401r.h头文件定义:
#define TIMER_A_CTL_MC__UP ((uint16_t)0x0010) /*!< Up mode: Timer counts up to TAxCCR0 */
通过 动态修改 TIMER_A0->CCR[1] 内容可以改变PWM间隔时间
通过DriverLib操作的方式输出PWM波形
/* Timer_A PWM Configuration Parameter */
Timer_A_PWMConfig pwmConfig =
{
TIMER_A_CLOCKSOURCE_SMCLK,
TIMER_A_CLOCKSOURCE_DIVIDER_1,
32000,
TIMER_A_CAPTURECOMPARE_REGISTER_1,
TIMER_A_OUTPUTMODE_RESET_SET,
3200
};
Timer_A_generatePWM(TIMER_A1_BASE, &pwmConfig);
Timer_A_setCompareValue(TIMER_A2_BASE, TIMER_A_CAPTURECOMPARE_REGISTER_1, PWM_PERIOD * (50/100.0f)); //动态设置PWM 间隔时间
而timer_a.C文件中对Timer_A_generatePWM函数定义如下
void Timer_A_generatePWM(uint32_t timer, const Timer_A_PWMConfig *config)
{
//此处省略一部分，参数合法判断...
privateTimer_AProcessClockSourceDivider(timer, config->clockSourceDivider);
TIMER_A_CMSIS(timer)->CTL &=
~(TIMER_A_CLOCKSOURCE_INVERTED_EXTERNAL_TXCLK + TIMER_A_UPDOWN_MODE
+ TIMER_A_DO_CLEAR + TIMER_A_TAIE_INTERRUPT_ENABLE);
TIMER_A_CMSIS(timer)->CTL |= (config->clockSource + TIMER_A_UP_MODE
+ TIMER_A_DO_CLEAR);
TIMER_A_CMSIS(timer)->CCR[0] = config->timerPeriod;
TIMER_A_CMSIS(timer)->CCTL[0] &= ~(TIMER_A_CAPTURECOMPARE_INTERRUPT_ENABLE
+ TIMER_A_OUTPUTMODE_RESET_SET);
uint8_t idx = (config->compareRegister>>1) - 1;
TIMER_A_CMSIS(timer)->CCTL[idx] |= config->compareOutputMode;
TIMER_A_CMSIS(timer)->CCR[idx] = config->dutyCycle;
}
可以看到相关操作与寄存器类似，但一次只能修改一路PWM输出。难怪官方例程中直接使用寄存器操作，多路输出更加容易控制。
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