Question
STM32F401CCU PCM5102A Sample Rate deviation
Hi All, I'm using an STM32F401CCU with a TI PCM5102A DAC. I've set up a simple DMA (code attached) and a naïve square wave function. My issue is that the generated square wave is at the 'wrong' frequency. In the code I am generating a 440 hz (or multiple) square wave at a sample rate of 32khz (set in the I2S section of the IOC).
I am using an accumulator to either set a double variable to low or high whether it is above or below 0.5. This value is then multiplied by 32767 and then added to an entry in a signed 16 bit array.
I2S peripheral clock is at 128 MHZ. I seem to be getting however around 374Hz indicating perhaps that the time increment isn't correct (and then the sample rate is not) any help much appreciated, am new to this
/* USER CODE BEGIN Header */
/**
******************************************************************************
* @file : main.c
* @brief : Main program body
******************************************************************************
* @attention
*
* Copyright (c) 2022 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
*/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "math.h"
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
#define SAMPLE_RATE 32000
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
I2S_HandleTypeDef hi2s3;
DMA_HandleTypeDef hdma_spi3_tx;
/* USER CODE BEGIN PV */
int16_t splx[16];
int16_t sample;
double T;
double Ts = 0.00003125;
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2S3_Init(void);
static void MX_DMA_Init(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
/* USER CODE END 0 */
/**
* @brief The application entry point.
* @retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_DMA_Init();
MX_I2S3_Init();
/* USER CODE BEGIN 2 */
HAL_I2S_Transmit_DMA(&hi2s3, (uint16_t*)splx,8);
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
/**
* @brief System Clock Configuration
* @retval None
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
/** Macro to configure the PLL multiplication factor
*/
__HAL_RCC_PLL_PLLM_CONFIG(8);
/** Macro to configure the PLL clock source
*/
__HAL_RCC_PLL_PLLSOURCE_CONFIG(RCC_PLLSOURCE_HSI);
/** Configure the main internal regulator output voltage
*/
__HAL_RCC_PWR_CLK_ENABLE();
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE2);
/** Initializes the RCC Oscillators according to the specified parameters
* in the RCC_OscInitTypeDef structure.
*/
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState = RCC_HSI_ON;
RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
Error_Handler();
}
/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief I2S3 Initialization Function
* @param None
* @retval None
*/
static void MX_I2S3_Init(void)
{
/* USER CODE BEGIN I2S3_Init 0 */
/* USER CODE END I2S3_Init 0 */
/* USER CODE BEGIN I2S3_Init 1 */
/* USER CODE END I2S3_Init 1 */
hi2s3.Instance = SPI3;
hi2s3.Init.Mode = I2S_MODE_MASTER_TX;
hi2s3.Init.Standard = I2S_STANDARD_PHILIPS;
hi2s3.Init.DataFormat = I2S_DATAFORMAT_16B;
hi2s3.Init.MCLKOutput = I2S_MCLKOUTPUT_DISABLE;
hi2s3.Init.AudioFreq = I2S_AUDIOFREQ_32K;
hi2s3.Init.CPOL = I2S_CPOL_LOW;
hi2s3.Init.ClockSource = I2S_CLOCK_PLL;
hi2s3.Init.FullDuplexMode = I2S_FULLDUPLEXMODE_ENABLE;
if (HAL_I2S_Init(&hi2s3) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN I2S3_Init 2 */
/* USER CODE END I2S3_Init 2 */
}
/**
* Enable DMA controller clock
*/
static void MX_DMA_Init(void)
{
/* DMA controller clock enable */
__HAL_RCC_DMA1_CLK_ENABLE();
/* DMA interrupt init */
/* DMA1_Stream5_IRQn interrupt configuration */
HAL_NVIC_SetPriority(DMA1_Stream5_IRQn, 0, 0);
HAL_NVIC_EnableIRQ(DMA1_Stream5_IRQn);
}
/**
* @brief GPIO Initialization Function
* @param None
* @retval None
*/
static void MX_GPIO_Init(void)
{
/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOC_CLK_ENABLE();
__HAL_RCC_GPIOH_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
__HAL_RCC_GPIOB_CLK_ENABLE();
}
/* USER CODE BEGIN 4 */
int16_t outputBuffer(){
#define TWOPI 6.28318530718
double sampledouble = 0;
T = T + (Ts*440);
if (T >= 1.0){
T = 0;
}
if (T < 0.5){
sampledouble = -0.8;
}
if (T >= 0.5){
sampledouble = 0.8;
}
//Normalise
sample = sampledouble * 32767;
return sample;
}
void HAL_I2S_TxHalfCpltCallback (I2S_HandleTypeDef * hi2s){
splx[0] = outputBuffer();
splx[1] = splx[0];
splx[2] = outputBuffer();
splx[3] = splx[2];
splx[4] = outputBuffer();
splx[5] = splx[4];
splx[6] = outputBuffer();
splx[7] = splx[6];
}
void HAL_I2S_TxCpltCallback (I2S_HandleTypeDef * hi2s){
splx[8] = outputBuffer();
splx[9] = splx[8];
splx[10]= outputBuffer();
splx[11]=splx[10];
splx[12]=outputBuffer();
splx[13]= splx[12];
splx[14]= outputBuffer();
splx[15]= splx[14];
}
/* USER CODE END 4 */
/**
* @brief This function is executed in case of error occurrence.
* @retval None
*/
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler_Debug */
/* User can add his own implementation to report the HAL error return state */
__disable_irq();
while (1)
{
}
/* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
* @brief Reports the name of the source file and the source line number
* where the assert_param error has occurred.
* @param file: pointer to the source file name
* @param line: assert_param error line source number
* @retval None
*/
void assert_failed(uint8_t *file, uint32_t line)
{
/* USER CODE BEGIN 6 */
/* User can add his own implementation to report the file name and line number,
ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
/* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */
