CC2541 再打开Timer3 和Timer4时，会触发P1.2外部中断

/******************************************************************************

 @file  buzzer.c

 @brief Control of the buzzer of the keyfob board in the CC2540DK-mini kit.

 Group: WCS, BTS
 Target Device: CC2540, CC2541

 ******************************************************************************
 
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 ******************************************************************************
 Release Name: ble_sdk_1.5.0.16
 Release Date: 2019-04-18 08:53:32
 *****************************************************************************/

#include "hal_mcu.h"
#include "buzzer.h"


/** \brief	Initialize buzzer
*
* This will initialize the buzzer
*
*/
void buzzerInit(void)
{
#if defined ( CC2540_MINIDK )
    // Buzzer connected at P1_6
    // We will use Timer 3 Channel 0 at alternate location 2
    // Channel 0 will toggle on compare with 0 and counter will
    // count in up/down mode to T3CC0.

    PERCFG |= 0x20;             // Timer 3 Alternate location 2
    P1DIR |= 0x40;              // P1_6 = output
    P1SEL |= 0x40;              // Peripheral function on P1_6

    T3CTL &= ~0x10;             // Stop timer 3 (if it was running)
    T3CTL |= 0x04;              // Clear timer 3
    T3CTL &= ~0x08;             // Disable Timer 3 overflow interrupts
    T3CTL |= 0x03;              // Timer 3 mode = 3 - Up/Down

    T3CCTL0 &= ~0x40;           // Disable channel 0 interrupts
    T3CCTL0 |= 0x04;            // Ch0 mode = compare
    T3CCTL0 |= 0x10;            // Ch0 output compare mode = toggle on compare
#endif
}

/** \brief	Starts the buzzer
*
* Starts the buzzer with given frequency
*
* \param[in]       frequency
*     The frequency in Hertz of the sound to output
* @return  1 successful - 0 if frequency invalid
*/
uint8 buzzerStart(uint16 frequency)
{
#if defined ( CC2540_MINIDK )
    buzzerInit();
  
    uint8 prescaler = 0;

    // Get current Timer tick divisor setting
    uint8 tickSpdDiv = (CLKCONSTA & 0x38)>>3;

    // Check if frequency too low
    if (frequency < (244 >> tickSpdDiv)){   // 244 Hz = 32MHz / 256 (8bit counter) / 4 (up/down counter and toggle on compare) / 128 (max timer prescaler)
        buzzerStop();                       // A lower tick speed will lower this number accordingly.
        return 0;
    }

    // Calculate nr of ticks required to achieve target frequency
    uint32 ticks = (8000000/frequency) >> tickSpdDiv;      // 8000000 = 32M / 4;

    // Fit this into an 8bit counter using the timer prescaler
    while ((ticks & 0xFFFFFF00) != 0)
    {
        ticks >>= 1;
        prescaler += 32;
    }

    // Update registers
    T3CTL &= ~0xE0;
    T3CTL |= prescaler;
    T3CC0 = (uint8)ticks;

    // Start timer
    T3CTL |= 0x10;
#endif
    
    return 1;
}

/** \brief	Stops the buzzer
*
* Turn off the buzzer
*
*/
void buzzerStop(void)
{
#if defined ( CC2540_MINIDK )
    T3CTL &= ~0x10;             // Stop timer 3
    P1SEL &= ~0x40;
    P1_6 = 0;
#endif
}