microphone.cpp

00001 #include "Microphone.h"
00002 
00003 bool _mic_toggle = false;
00004 uint8_t _mic_pulses= 0;
00005 uint8_t _mic_pulses_buffered = 0;
00006 uint8_t _mic_counter = 0;
00007 DigitalIn* _mic_d;
00008 DigitalOut* _mic_clk;
00009 
00010 void _mic_timer_int()
00011 {
00012     // If clock output to mic is low, read data pin and increment
00013     // pulse count if it's high.
00014     if (!_mic_toggle) {
00015         _mic_counter += 1;
00016         if (_mic_counter == 0) {
00017             _mic_pulses_buffered = _mic_pulses;
00018             _mic_pulses = 0;
00019         }
00020         if (_mic_d->read()) _mic_pulses++;
00021     }
00022     
00023     // Toggle clock output to mic
00024     _mic_toggle = !_mic_toggle;
00025     _mic_clk->write(_mic_toggle);
00026     
00027     // Clear interrupt
00028     TIM3->SR &= ~TIM_SR_UIF;
00029 }
00030 
00031 Microphone::Microphone()
00032 {
00033     this->isStarted = false;
00034 }
00035 
00036 void Microphone::start()
00037 {
00038     if (!this->isStarted) {
00039         // Two pins: clock to microphone and data from microphone.
00040         _mic_d = new DigitalIn(PC_3);
00041         _mic_clk = new DigitalOut(PB_10);
00042         
00043         // Use timer 3 to sample from the MP45DT02 microphone.
00044         
00045         // Enable timer.
00046         RCC->APB1ENR |= RCC_APB1ENR_TIM3EN;
00047         
00048         // Scale timer so ticks are 100ns
00049         uint32_t PCLK = SystemCoreClock / 4;
00050         uint32_t prescale = PCLK / 10000000; // 10Mhz (100ns ticks)
00051         TIM3->PSC = prescale - 1;
00052         
00053         // Enable counter
00054         TIM3->CR1 |= TIM_CR1_CEN;
00055     
00056         // Set auto-reset after five ticks (500ns).
00057         TIM3->ARR = 4;
00058         
00059         // Re-initialize counter.
00060         TIM3->EGR |= TIM_EGR_UG;
00061 
00062         // Set up and enable interrupt for when timer overflows.
00063         NVIC_SetVector(TIM3_IRQn, (uint32_t)_mic_timer_int);
00064         NVIC_EnableIRQ(TIM3_IRQn);
00065         TIM3->DIER |= TIM_DIER_UIE;
00066         this->isStarted = true;
00067     }
00068 }
00069 
00070 void Microphone::stop() // Not tested!
00071 {
00072     if (this->isStarted) {
00073         // Disable interrupts.
00074         NVIC_SetVector(TIM3_IRQn, (uint32_t)_mic_timer_int);
00075         NVIC_DisableIRQ(TIM3_IRQn);
00076         TIM3->DIER &= ~TIM_DIER_UIE;
00077             
00078         // Disable counter
00079         TIM3->CR1 &= ~TIM_CR1_CEN;    
00080             
00081         // Disable timer.
00082         RCC->APB1ENR &= ~RCC_APB1ENR_TIM3EN;
00083             
00084         // Clear interrupt
00085         TIM3->SR &= ~TIM_SR_UIF;
00086         
00087         delete _mic_d; _mic_d = NULL;
00088         delete _mic_clk; _mic_clk = NULL;
00089     }
00090 }
00091 
00092 signed char Microphone::read()
00093 {
00094     if (this->isStarted) {
00095         return (int8_t)((uint16_t)_mic_pulses_buffered - 128);
00096     } else {
00097         return 0;
00098     }
00099 }