dac.c File Reference

#include "dac.h"
#include "timer.h"
#include <LPC17xx.h>

Go to the source code of this file.

Macros
#define	DAC_CLK_HZ   25000000
#define	DAC_SIN_TABLE_SZ   45

Functions
_PRIVATE u16	adjust_sample_volume (u16 sample, u8 volume)
_PRIVATE void	next_sample (void)
void	DAC_BUZInit (u8 timer_a, u8 timer_b, u8 int_priority)
	Initializes the DAC peripheral.
void	DAC_BUZDeinit (void)
void	DAC_BUZSetVolume (u8 volume)
	Sets the volume of the buzzer.
void	DAC_BUZPlay (DAC_Tone tone, u16 bpm)
	Plays the given note for the given duration.
bool	DAC_BUZIsPlaying (void)
void	DAC_BUZStop (void)

Variables
_PRIVATE TIMER	DAC_SamplesTimer
_PRIVATE TIMER	DAC_SecondsTimer
_PRIVATE u8	DAC_SinVolume = DAC_VOL_DEFAULT
_PRIVATE u32	DAC_SinTableIndex = 0
const u16	DAC_Sin []
	Sine wave samples for the DAC. They represent one complete period. Each sample needs to be sent to the DAC.

Macro Definition Documentation

DAC_CLK_HZ

#define DAC_CLK_HZ   25000000

Definition at line 5 of file dac.c.

DAC_SIN_TABLE_SZ

#define DAC_SIN_TABLE_SZ   45

Definition at line 6 of file dac.c.

Function Documentation

adjust_sample_volume()

_PRIVATE u16 adjust_sample_volume ( u16  sample, u8  volume  )

inline

Definition at line 34 of file dac.c.

{
    if (volume == 0)
        return 0; // Mute
 
    sample -= 410;
    sample /= (10 / volume); // If volume is 1 -> sample /= 10 (decrease volume), if 10 -> sample /= 1 (increase volume)
    sample += 410;
 
    return sample;
}

DAC_BUZDeinit()

void DAC_BUZDeinit

(

void

)

Definition at line 76 of file dac.c.

{
    LPC_PINCON->PINSEL1 &= ~(3 << 20);
    LPC_GPIO0->FIODIR &= ~(1 << 26);
 
    DAC_BUZStop();
    TIMER_Deinit(DAC_SamplesTimer);
    TIMER_Deinit(DAC_SecondsTimer);
}

DAC_BUZInit()

void DAC_BUZInit	(	u8	timer_a,
		u8	timer_b,
		u8	int_priority
	)

Initializes the DAC peripheral.

Parameters

int_priority

The interrupt priority of the timer. If set to INT_PRIO_DEF, the default interrupt priority will be used.

Note

This implementation requires the use of 2 timers to feed the DAC with samples and to play the note for the given duration. By giving these parameters to this function, you ensure that those timers are not and won't be used for other purposes.

Definition at line 66 of file dac.c.

{
    // Enable Analog OUT (function 10) on PIN on P0.26, located in PINSEL1
    LPC_PINCON->PINSEL1 |= (2 << 20);
    LPC_GPIO0->FIODIR |= (1 << 26);
 
    TIMER_Init(&DAC_SamplesTimer, timer_a, NO_PRESCALER, int_priority);
    TIMER_Init(&DAC_SecondsTimer, timer_b, NO_PRESCALER, int_priority);
}

DAC_BUZIsPlaying()

bool DAC_BUZIsPlaying

(

void

)

Definition at line 114 of file dac.c.

{
    return TIMER_IsEnabled(DAC_SamplesTimer) && TIMER_IsEnabled(DAC_SecondsTimer);
}

DAC_BUZPlay()

void DAC_BUZPlay	(	DAC_Tone	tone,
		u16	bpm
	)

Plays the given note for the given duration.

Parameters

tone	The tone to be played
bpm	The tempo of the note (i.e. 60, 120, 240, etc.)

Definition at line 91 of file dac.c.

{
    // How many samples need to be sent to the DAC in a second in order to play the tone
    TIMER_SetInterruptHandler(DAC_SamplesTimer, TIM_INT_SRC_MR0, next_sample);
    TIMER_SetMatch(DAC_SamplesTimer, (TIMER_MatchRegister){.which = TIM_MR0,
                                                           .actions = TIM_MR_INT | TIM_MR_RES,
                                                           .match = get_tone_timing(tone.note, tone.octave)});
 
    // Since a tone has a type (i.e. a duration which depends on the BPM), the duration of the tone
    // needs to be controlled by another timer, which, on match, will stop & clear the samples timer.
    // The duration (in seconds) of the tone is calculated by the formula: (60 * type) / bpm. Since
    // each second the seconds timer ticks 25 million times, we need to multiply that by the duration
    const u32 tone_duration = DAC_CLK_HZ * ((60 * tone.type) / bpm);
    TIMER_SetInterruptHandler(DAC_SecondsTimer, TIM_INT_SRC_MR0, DAC_BUZStop);
    TIMER_SetMatch(DAC_SecondsTimer, (TIMER_MatchRegister){.which = TIM_MR0,
                                                           .actions = TIM_MR_INT | TIM_MR_RES | TIM_MR_STP,
                                                           .match = tone_duration});
 
    // Starts the timers (i.e. plays)
    TIMER_Enable(DAC_SamplesTimer);
    TIMER_Enable(DAC_SecondsTimer);
}

DAC_BUZSetVolume()

void DAC_BUZSetVolume

(

u8

volume

)

Sets the volume of the buzzer.

Parameters

volume

The volume of the buzzer (between 0 and 10).

Definition at line 86 of file dac.c.

{
    DAC_SinVolume = (IS_BETWEEN_EQ(volume, 0, 10)) ? volume : DAC_VOL_DEFAULT;
}

DAC_BUZStop()

void DAC_BUZStop

(

void

)

Definition at line 119 of file dac.c.

{
    DAC_SinVolume = DAC_VOL_DEFAULT;
    DAC_SinTableIndex = 0;
    LPC_DAC->DACR &= ~(0x3FF << 6);
 
    TIMER_Disable(DAC_SamplesTimer);
    TIMER_Reset(DAC_SamplesTimer);
 
    TIMER_Reset(DAC_SecondsTimer);
    TIMER_Disable(DAC_SecondsTimer);
}

next_sample()

_PRIVATE void next_sample

(

void

)

Definition at line 48 of file dac.c.

{
    if (DAC_SinVolume == 0)
    {
        LPC_DAC->DACR = 0;
        return;
    }
 
    // Sending next sample
    u16 volumed_sample = adjust_sample_volume(DAC_Sin[DAC_SinTableIndex++], DAC_SinVolume);
    LPC_DAC->DACR = (volumed_sample << 6);
 
    if (DAC_SinTableIndex == DAC_SIN_TABLE_SZ)
        DAC_SinTableIndex = 0;
}

Variable Documentation

DAC_SamplesTimer

_PRIVATE TIMER DAC_SamplesTimer

Definition at line 8 of file dac.c.

DAC_SecondsTimer

_PRIVATE TIMER DAC_SecondsTimer

Definition at line 9 of file dac.c.

DAC_Sin

const u16 DAC_Sin[]

Initial value:

= {410, 467, 523, 576, 627, 673, 714, 749, 778, 799, 813, 819, 817, 807, 789,
                       764, 732, 694, 650, 602, 550, 495, 438, 381, 324, 270, 217, 169, 125, 87,
                       55,  30,  12,  2,   0,   6,   20,  41,  70,  105, 146, 193, 243, 297, 353}

Sine wave samples for the DAC. They represent one complete period. Each sample needs to be sent to the DAC.

Definition at line 16 of file dac.c.

                      {410, 467, 523, 576, 627, 673, 714, 749, 778, 799, 813, 819, 817, 807, 789,
                       764, 732, 694, 650, 602, 550, 495, 438, 381, 324, 270, 217, 169, 125, 87,
                       55,  30,  12,  2,   0,   6,   20,  41,  70,  105, 146, 193, 243, 297, 353};

DAC_SinTableIndex

_PRIVATE u32 DAC_SinTableIndex = 0

Definition at line 12 of file dac.c.

DAC_SinVolume

_PRIVATE u8 DAC_SinVolume = DAC_VOL_DEFAULT

Definition at line 11 of file dac.c.