Embedded Systems: Basic Timers

定时器

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（一）工作原理

1.定时器：计数器,时钟脉冲计数

2.工作原理：

（1）Automatic counting mode：Under the condition of the clock,The system automatically count to the maximum overflow,Represents a timing to complete

• The clock a maximum count is determined by the timer of digit $2^n$

（2）Counting modulation mode：用户Custom timing time,System clock to the custom time,Represents a timing to complete

	由上可知,Have more flexibility in modulation counting mode.

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向上计数：After counting up to the set point to count,周期循环

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连续计数：After counting up to a maximum count again,周期循环

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上/下计数：After counting up to the set value,From the set point counting down again

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（二）分类

1.In the nuclear timer

（1）SysTick定时器：系统时钟滴答定时器（Timing function）

• Can be used as an operating system scheduling time slice

（2）RTC：实时时钟

（3）WatchDog：看门狗时钟,For abnormal reset

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2.Peripherals timer

（1）基本定时器：Timing function,For other time base timer function

（2）通用定时器

• 输入捕获
• 输出比较
• PWM（A special case of our output compare mode）

（3）高级定时器

• 通用定时器
• With dead zone controlPWM
• The road three phase shift waveform（Three-phase motor control）

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（三）编程

1.编程流程

（1）时钟配置

• 时钟源
• 分频系数

（2）功能配置

• 计数模式
• 重装载值
• 计数值清零

（3）定时器使能

（4）中断配置

• 中断源
• 中断优先级
• 中断使能

（5）中断处理函数

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2.编程实例

（1）寄存器版本

#include "msp.h"
#include "driverlib.h"

int main()
{
    
	//关闭看门狗
	WDTCTL = WDTPW | WDTHOLD;
	
	//GPIO复用为HFXT
	PJ->SEL1 &=~(BIT2 | BIT3);
	PJ->SEL0 |= (BIT2 | BIT3);
	
	//Unlock the clock register（0x695A)
	CS->KEY = CS_KEY;
	
	//HCLK 16MHz
	CS->CTL2 |= CS_CTL2_HFXTFREQ_2 | CS_CTL2_HFXTDRIVE | CS_CTL2_HFXT_EN;
	//SMCLK 4MHz
	CS->CTL1 |= CS_CTL1_DIVS_2 | CS_CTL1_SELS_5;
	//SMCLK 时钟源使能
	CS->CLKEN |= CS_CLKEN_SMCLK_EN;
	
	//Lock the clock register（0xA569)
	CS->KEY = CS_KEY_KEY_OFS;
	
	//时钟选择(1MHz)
	TIMER_A0->CTL |= TIMER_A_CTL_SSEL__SMCLK | TIMER_A_CTL_ID__4;
	
	//计数值1ms
	TIMER_A0->R = 999;
	
	//Rising counting mode,计数值清零
	TIMER_A0->CTL |= TIMER_A_CTL_MC__UP | TIMER_A_CTL_CLR;
	
	//清除中断标志位
	TIMER_A0->CTL &= ~TIMER_A_CTL_IFG;
	//Timer中断使能
	TIMER_A0->CTL |= TIMER_A_CTL_IE;
	
	
	P1->SEL0 &=~BIT0;
	P1->SEL1 &=~BIT0;
	
	P1->DIR |= BIT0;
	P1->OUT |= BIT0;

	while(1);

	return 0;
}

uint8_t timecount = 0;
void TA0_N_IRQHandler(void)
{
    
	//判断中断是否发生
	if(TIMER_A_CTL_IFG & TIMER_A0->CTL)
	{
    
		//中断标志位清零
		TIMER_A0->CTL &= ~TIMER_A_CTL_IFG;
		timecount++;
		if(timecount == 10)
		{
    
			P1->OUT ^= BIT0;
		}
	}
}

（2）库函数版本

#include "msp.h"
#include "driverlib.h"

int main()
{
    
	//关闭看门狗
	WDT_A_holdTimer();
	
	//GPIO复用为HFXT
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_PJ,GPIO_PIN3 | GPIO_PIN2, GPIO_PRIMARY_MODULE_FUNCTION);
	
	//HCLK 16MHz
	CS_setExternalClockSourceFrequency(32000,16000000);
	CS_startHFXT(false);
	
	//SMCLK 4MHz
	CS_initClockSignal(CS_SMCLK,CS_HFXTCLK_SELECT, CS_CLOCK_DIVIDER_4);
	CS_enableClockRequest(CS_SMCLK);
	
	//The timer function configuration
	Timer_A_UpModeConfig Timer_A_UpMode;
	
	Timer_A_UpMode.clockSource 								= TIMER_A_CLOCKSOURCE_SMCLK;
	Timer_A_UpMode.clockSourceDivider						= TIMER_A_CLOCKSOURCE_DIVIDER_4;
	Timer_A_UpMode.timerPeriod								= 999;
	Timer_A_UpMode.timerClear								= TIMER_A_DO_CLEAR;
	Timer_A_UpMode.timerInterruptEnable_TAIE				= TIMER_A_TAIE_INTERRUPT_DISABLE;
	Timer_A_UpMode.captureCompareInterruptEnable_CCR0_CCIE	= TIMER_A_CCIE_CCR0_INTERRUPT_DISABLE;
	
	//The timer function configuration
	Timer_A_configureUpMode(TIMER_A0_BASE,&Timer_A_UpMode);
	//清除中断标志位
	Timer_A_clearInterruptFlag(TIMER_A0_BASE);
	//使能中断
	Timer_A_enableInterrupt(TIMER_A0_BASE);
	//Can make the timer count
	Timer_A_startCounter(TIMER_A0_BASE, TIMER_A_UP_MODE);

	while(1);

	return 0;
}


uint8_t timecount = 0;
void TA0_N_IRQHandler(void)
{
    
	uint32_t status = Timer_A_getInterruptStatus(TIMER_A0_BASE);
	//判断中断是否发生
	if(TIMER_A_CTL_IFG & status)
	{
    
		//中断标志位清零
		Timer_A_clearInterruptFlag(TIMER_A0_BASE);
		timecount++;
		if(timecount == 10)
		{
    
			GPIO_toggleOutputOnPin(GPIO_PORT_P1,GPIO_PIN0);
		}
	}
}