CH32 Oscillator

In order to get to know the CH32V307 MCU better I decided to create a dual oscillator using the DACs.

Timer

A timer will be responsible for the sample frequency. The timer will be configured to run at 48000 Hz and it will generate an Update event for each clock.

void Timer4_Init (void) {
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure = { 0 };
    RCC_APB1PeriphClockCmd (RCC_APB1Periph_TIM4, ENABLE);

    TIM_TimeBaseStructInit (&TIM_TimeBaseStructure);
    TIM_TimeBaseStructure.TIM_Period = 3000 - 1;
    TIM_TimeBaseStructure.TIM_Prescaler = 0;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit (TIM4, &TIM_TimeBaseStructure);

    TIM_SelectOutputTrigger (TIM4, TIM_TRGOSource_Update);
    TIM_Cmd (TIM4, ENABLE);
}

A Period of 3000 will give us our desired 48000 Hz (144000000 / 3000 = 48000).

DMA

void Dac_Dma_Init (void) {
    DMA_InitTypeDef DMA_InitStructure = { 0 };
    RCC_AHBPeriphClockCmd (RCC_AHBPeriph_DMA2, ENABLE);

    DMA_StructInit (&DMA_InitStructure);
    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) &(DAC->RD12BDHR);
    DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t) &dac_buffer[0];
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
    DMA_InitStructure.DMA_BufferSize = 2 * BUFFER_SIZE;
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Word;
    DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
    DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;
    DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;

    DMA_Init (DMA2_Channel3, &DMA_InitStructure);

    DMA_ITConfig (DMA2_Channel3, DMA_IT_TC, ENABLE);
    DMA_ITConfig (DMA2_Channel3, DMA_IT_HT, ENABLE);

    DMA_Cmd (DMA2_Channel3, ENABLE);

}

DAC

void Dual_Dac_Init (void) {
    GPIO_InitTypeDef GPIO_InitStructure = { 0 };
    DAC_InitTypeDef DAC_InitType = { 0 };

    // Make sure the APB busses are clocked
    RCC_APB2PeriphClockCmd (RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd (RCC_APB1Periph_DAC, ENABLE);

    // Configure PA4 and PA5 for analog output
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init (GPIOA, &GPIO_InitStructure);
    GPIO_SetBits (GPIOA, GPIO_Pin_4);

    // Throw a debug pulse out on PA6
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init (GPIOA, &GPIO_InitStructure);

    // DAC convertion triggered by Timer 4
    DAC_InitType.DAC_Trigger = DAC_Trigger_T4_TRGO;
    DAC_InitType.DAC_WaveGeneration = DAC_WaveGeneration_None;
    DAC_InitType.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bit0;
    DAC_InitType.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init (DAC_Channel_1, &DAC_InitType);
    DAC_Init (DAC_Channel_2, &DAC_InitType);

    DAC_Cmd (DAC_Channel_1, ENABLE);
    DAC_Cmd (DAC_Channel_2, ENABLE);

    DAC_DMACmd (DAC_Channel_1, ENABLE);
    DAC_DMACmd (DAC_Channel_2, ENABLE);

    DAC_SetDualChannelData (DAC_Align_12b_R, 0x123, 0x321);
}

DMA Interrupt

void DMA_Interrupt_Init () {
    /*Configuration interrupt priority*/
    NVIC_InitTypeDef NVIC_InitStructure = { 0 };
    NVIC_InitStructure.NVIC_IRQChannel = DMA2_Channel3_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; //Seeing priority
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; //Response priority
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //Enable
    NVIC_Init (&NVIC_InitStructure);
}

Oscillator Calculation

__attribute__((interrupt("WCH-Interrupt-fast"))) void DMA2_Channel3_IRQHandler () {

    // To time the ISR throw debug out hi
    GPIO_WriteBit (GPIOA, GPIO_Pin_6, Bit_SET);

    if (DMA_GetITStatus (DMA2_IT_TC3) != RESET) {
        ++full_count;
        update_dac_buffer (&dac_buffer[BUFFER_SIZE]);
        DMA_ClearITPendingBit (DMA2_IT_TC3);
    }
    else if (DMA_GetITStatus (DMA2_IT_HT3) != RESET) {
        ++half_count;
        update_dac_buffer (&dac_buffer[0]);
        DMA_ClearITPendingBit (DMA2_IT_HT3);
    }

    // Finally toggle debug out low again
    GPIO_WriteBit (GPIOA, GPIO_Pin_6, Bit_RESET);

}

static inline void update_dac_buffer (uint32_t *buffer_address) {
    for (uint8_t sample = 0; sample < BUFFER_SIZE; ++sample) {
        for (uint8_t oscillator = 0; oscillator < 2; ++oscillator) {
            osc[oscillator].last_value = osc[oscillator].amplitude * sinf (osc[oscillator].angle);
            osc[oscillator].angle += osc[oscillator].angle_per_sample; // rotate
            if (osc[oscillator].angle > M_TWOPI)
                osc[oscillator].angle -= M_TWOPI; // roll over
        }
        buffer_address[sample] = (((uint16_t) (MID_POINT + MID_POINT * osc[1].last_value)) << 16) | ((uint16_t) (MID_POINT + MID_POINT * osc[0].last_value));
    }
}

Miscellaneous Links

• Project on Github