SMT-0540-S-R Buzzer at p1.6

/**************************************************************************************************
  Filename:       buzzer.c
  Revised:        $Date: 2012-10-11 12:11:30 -0700 (Thu, 11 Oct 2012) $
  Revision:       $Revision: 31784 $

  Description:    Control of the buzzer of the keyfob board in the CC2540DK-mini
                  kit.

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  granted under the terms of a software license agreement between the user
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  Software unless you agree to abide by the terms of the License. The License
  limits your use, and you acknowledge, that the Software may not be modified,
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  or used solely and exclusively in conjunction with a Texas Instruments radio
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**************************************************************************************************/

#include "buzzer.h"
#include "ioCC2540.h"

/** \brief	Initialize buzzer
*
* This will initialize the buzzer
*
*/
void buzzerInit(void)
{
    // 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

}

/** \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)
{
    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    
    while ((ticks & 0xFFFFFF00) != 0)
    {
        ticks >>= 1;
        prescaler += 32;
        
    } 

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

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

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