audio.c

#include <stdint.h>
#include <string.h>

#include "stm32f4xx_dac.h"

#include "nlr.h"
#include "misc.h"
#include "mpconfig.h"
#include "qstr.h"
#include "parse.h"
#include "obj.h"
#include "runtime.h"

#include "audio.h"

STATIC void TIM7_Config(uint freq) {
    // TIM7 clock enable
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM7, ENABLE);

    // reset TIM7
    TIM_DeInit(TIM7);

    // Compute the prescaler value so TIM7 triggers at freq-Hz
    uint16_t period = (uint16_t) ((SystemCoreClock / 2) / freq) - 1;

    // Time base configuration
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    TIM_TimeBaseStructure.TIM_Period = period; // timer triggers with this period
    TIM_TimeBaseStructure.TIM_Prescaler = 0; // timer runs at SystemCoreClock / 2
    TIM_TimeBaseStructure.TIM_ClockDivision = 0; // unused for TIM7
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; // unused for TIM7
    TIM_TimeBaseInit(TIM7, &TIM_TimeBaseStructure);

    // TIM7 TRGO selection
    TIM_SelectOutputTrigger(TIM7, TIM_TRGOSource_Update);

    // TIM7 enable counter
    TIM_Cmd(TIM7, ENABLE);
}

/******************************************************************************/
// Micro Python bindings

typedef struct _pyb_audio_t {
    mp_obj_base_t base;
    uint dac_channel; // DAC_Channel_1 or DAC_Channel_2
    DMA_Stream_TypeDef *dma_stream; // DMA1_Stream6 or DMA1_Stream7
} pyb_audio_t;

mp_obj_t pyb_audio_noise(mp_obj_t self_in, mp_obj_t freq) {
    pyb_audio_t *self = self_in;

    // set TIM7 to trigger the DAC at the given frequency
    TIM7_Config(mp_obj_get_int(freq));

    DAC_Cmd(self->dac_channel, DISABLE);

    DAC_InitTypeDef DAC_InitStructure;
    DAC_InitStructure.DAC_Trigger = DAC_Trigger_T7_TRGO;
    DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_Noise;
    DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bits10_0;
    DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init(self->dac_channel, &DAC_InitStructure);

    DAC_Cmd(self->dac_channel, ENABLE);

    if (self->dac_channel == DAC_Channel_1) {
        DAC_SetChannel1Data(DAC_Align_12b_L, 0x7ff0);
    } else {
        DAC_SetChannel2Data(DAC_Align_12b_L, 0x7ff0);