Nucleo-H753ZI SPI Slave DMA continuously outputs 0xFF 0xFF 0xFF 0xFF; cannot transmit data

Harikrishnan · ‎2025-12-11

Hello ST Community,

am working with a Nucleo-H753ZI board where the STM32H753ZI is configured as an SPI1 slave, and the SPI master is a TI AM64x R5F core.
The goal is for the STM32 to continuously transmit 4-byte frames over SPI (using DMA) whenever the master clocks the bus.

However, the problem is:The master is receives only FF FF

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2025 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"
#include "string.h"
#include "stdio.h"
#include "stdarg.h"
#include "math.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */

/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */

/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
ADC_HandleTypeDef hadc3;
DMA_HandleTypeDef hdma_adc3;

SPI_HandleTypeDef hspi1;
DMA_HandleTypeDef hdma_spi1_tx;

TIM_HandleTypeDef htim6;

UART_HandleTypeDef huart3;

/* USER CODE BEGIN PV */

#define UART_HANDLE huart3
#define SPI_HANDLE  hspi1

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
void PeriphCommonClock_Config(void);
static void MPU_Config(void);
static void MX_GPIO_Init(void);
static void MX_BDMA_Init(void);
static void MX_DMA_Init(void);
static void MX_TIM6_Init(void);
static void MX_USART3_UART_Init(void);
static void MX_ADC3_Init(void);
static void MX_SPI1_Init(void);
/* USER CODE BEGIN PFP */
static inline uint32_t raw_to_mV(uint32_t raw16);
static void Build_SPI_Sample(uint8_t out[4], uint16_t adc_value, uint16_t sample_index);
static void Process_Block(const uint16_t *p, uint32_t N);


/* callbacks  */
void HAL_ADC_ConvHalfCpltCallback(ADC_HandleTypeDef *hadc);
void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef *hadc);
void HAL_SPI_TxCpltCallback(SPI_HandleTypeDef *hspi);

/* UART helpers */
static void uart_printf(const char *fmt, ...);

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/*  ADC + SPI working buffers  */

/*  ADC DMA buffer in RAM_D3  */
__attribute__((section(".RAM_D3")))
__attribute__((aligned(32)))
uint16_t adcBuf[480];            /* 480 samples -> two half-buffers of 240 */

static uint16_t shadow_half[240];
static volatile uint8_t shadow_valid = 0;

/*  SPI slave TX state + double buffer  (4 bytes per sample, ping-pong) */

__attribute__((section(".RAM_D3")))
__attribute__((aligned(32)))
uint8_t spi_tx[2][4];

static volatile uint8_t spi_busy     = 0;  /* 1 while a DMA TX is running */
volatile uint8_t        spi_tx_free  = 0;  /* index (0/1) FREE to rebuild next frame */
volatile uint8_t        spi_tx_in_use= 0;  /* index (0/1) currently armed for TX    */

static uint16_t g_sample_index = 0;        /* rolls 0..65535, placed in frame [2..3] */
volatile uint8_t pending_half  = 0;        /* 0 -> [0..239], 1 -> [240..479]         */
static volatile uint8_t last_half = 0;     /* 0 = first half, 1 = second              */

/*  Statistics / thresholds   */

#define STAT_WIN_N  240U         /* half-buffer = 240 samples */
#define HALF_COUNT  STAT_WIN_N

/* Board supply in mV (measured VDDA ) */
#ifndef VREF_MV
#define VREF_MV 3260UL
#endif

/* AC/DC decision thresholds (with hysteresis), in mV */
#define AC_P2P_HI_MV 150U   /* enter AC if >= 150 mV p-p and >= 100 mVrms */
#define AC_RMS_HI_MV 100U
#define AC_P2P_LO_MV 75U    /* return to DC if <= 75 mV p-p and <= 70 mVrms */
#define AC_RMS_LO_MV 70U

/* Running stats (RAW units). Only updated in thread context. */
volatile uint32_t win_mean_raw = 0;
volatile uint32_t win_rms_raw  = 0;
volatile uint16_t win_min_raw  = 0xFFFF;
volatile uint16_t win_max_raw  = 0x0000;

/* Same stats converted to millivolts (for printing/thresholds) */
volatile uint32_t win_mean_mv  = 0;
volatile uint32_t win_rms_mv   = 0;
volatile uint32_t win_min_mv   = 0;
volatile uint32_t win_max_mv   = 0;

/* 0 = DC, 1 = AC (decided with hysteresis) */
volatile uint8_t  signal_is_ac  = 0;

/* flag set by ADC DMA callbacks, consumed in main loop */
volatile uint8_t  stats_pending = 0;

/* RAW -> mV helper */
static inline uint32_t raw_to_mV(uint32_t raw16)
{
    return (uint32_t)((uint64_t)raw16 * (uint64_t)VREF_MV / 65535ULL);
}

/*   UART DMA ring buffer (printf)  */

/* Asynchronous UART TX ring + state for DMA-driven uart_printf() */
#define TXBUF_SIZE 1024
static volatile uint16_t tx_head = 0;   /* next write index */
static volatile uint16_t tx_tail = 0;   /* next DMA start   */
static volatile uint8_t  tx_dma_busy = 0;

/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MPU Configuration--------------------------------------------------------*/
  MPU_Config();

  /* 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();

  /* Configure the peripherals common clocks */
  PeriphCommonClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_BDMA_Init();
  MX_DMA_Init();
  MX_TIM6_Init();
  MX_USART3_UART_Init();
  MX_ADC3_Init();
  MX_SPI1_Init();
  /* USER CODE BEGIN 2 */

  /* USER CODE BEGIN 2 */

  HAL_Delay(500);
  /* 1) Start ADC3 + DMA (480 samples total => two halves of 240) */

  if (HAL_ADC_Start_DMA(&hadc3, (uint32_t*)adcBuf, 480U) != HAL_OK) {
      uart_printf("ADC DMA START FAILED\r\n");
  }

  /* 2) Prime SPI ping-pong buffers (4 bytes each) */
  uint16_t seed = shadow_valid ? shadow_half[STAT_WIN_N - 1] : 0;
  Build_SPI_Sample(spi_tx[0], seed, g_sample_index++);
  Build_SPI_Sample(spi_tx[1], seed, g_sample_index++);

  /* Mark one buffer FREE and one IN USE before starting DMA */
  spi_tx_free   = 1;   /* buffer 1 can be rebuilt next */
  spi_tx_in_use = 0;   /* buffer 0 is armed for TX     */
  spi_busy      = 0;

  /* 3) Start SPI1 slave TX DMA (master must clock SCK/NSS) */
  if (HAL_SPI_Transmit_DMA(&SPI_HANDLE, spi_tx[spi_tx_in_use], sizeof(spi_tx[0])) == HAL_OK) {
      spi_busy = 1;
  } else {
      uart_printf("SPI DMA START FAILED\r\n");
      spi_busy = 0;  /* keep running in UART-only mode */
  }

  /* 4) Start TIM6 – triggers ADC conversions at the sample rate */
  if (HAL_TIM_Base_Start(&htim6) != HAL_OK) {
      uart_printf("TIM6 START FAILED\r\n");
  }

  /* 5) Banner */
  uart_printf("System ready - ADC+DMA active; SPI slave primed; UART debug enabled\r\n");

  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  /* Infinite loop */
  /* Infinite loop */
  while (1)
  {
      /* 1) If a fresh 240-sample block was frozen, process it here  */
      if (stats_pending) {
          __disable_irq();
          uint8_t half = pending_half;
          stats_pending = 0;
          __enable_irq();

          const uint16_t *src=&adcBuf[ half ? 240 : 0 ];
          memcpy(shadow_half, src, STAT_WIN_N * sizeof(uint16_t));

          Process_Block(shadow_half, STAT_WIN_N);
      }

      /* 2) Print at most every 500 ms over UART */
      static uint32_t last_print_ms = 0;
      uint32_t now = HAL_GetTick();
      if (now - last_print_ms >= 500) {
          last_print_ms = now;

          uint32_t mean_raw, mean_mv, rms_mv, min_mv, max_mv;
          uint8_t  is_ac;

          __disable_irq();
          mean_raw = win_mean_raw;
          mean_mv  = win_mean_mv;
          rms_mv   = win_rms_mv;
          min_mv   = win_min_mv;
          max_mv   = win_max_mv;
          is_ac    = signal_is_ac;
          __enable_irq();

          uint32_t vpp_mv = (max_mv >= min_mv) ? (max_mv - min_mv) : 0U;

          if (is_ac) {
              uart_printf("Mode: AC  raw=%lu  Vrms=%lumV  Vpp=%lumV\r\n",
                          (unsigned long)mean_raw,
                          (unsigned long)rms_mv,
                          (unsigned long)vpp_mv);
          } else {
              uart_printf("Mode: DC  raw=%lu  Vmean=%lu.%03luV\r\n",
                          (unsigned long)mean_raw,
                          (unsigned long)(mean_mv / 1000UL),
                          (unsigned long)(mean_mv % 1000UL));
          }
      }

      /* 3) Simple SPI slave TX: send one 4-byte frame every time TI clocks us */
      {
          uint8_t  frame[4];

          /* Use latest mean_raw as the sample (cast to 16-bit).
             You can change this to adcBuf[0] or any other sample if you want. */
          uint16_t sample = (uint16_t)win_mean_raw;

          Build_SPI_Sample(frame, sample, g_sample_index++);

          /* This blocks until the TI MCSPI master pulls NSS low and clocks 4 bytes */
          if (HAL_SPI_Transmit(&SPI_HANDLE, frame, sizeof(frame), HAL_MAX_DELAY) != HAL_OK)
          {
              uart_printf("SPI TX error, err=0x%lx\r\n",
                          (unsigned long)HAL_SPI_GetError(&SPI_HANDLE));
          }
      }
  }


    /* 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};

  /** Supply configuration update enable
  */
  HAL_PWREx_ConfigSupply(PWR_LDO_SUPPLY);

  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

  while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}

  /** 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_DIV1;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
  RCC_OscInitStruct.PLL.PLLM = 8;
  RCC_OscInitStruct.PLL.PLLN = 48;
  RCC_OscInitStruct.PLL.PLLP = 4;
  RCC_OscInitStruct.PLL.PLLQ = 2;
  RCC_OscInitStruct.PLL.PLLR = 2;
  RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_3;
  RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
  RCC_OscInitStruct.PLL.PLLFRACN = 0;
  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_CLOCKTYPE_D3PCLK1|RCC_CLOCKTYPE_D1PCLK1;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV4;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV1;
  RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief Peripherals Common Clock Configuration
  * @retval None
  */
void PeriphCommonClock_Config(void)
{
  RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};

  /** Initializes the peripherals clock
  */
  PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_ADC|RCC_PERIPHCLK_SPI1;
  PeriphClkInitStruct.PLL2.PLL2M = 4;
  PeriphClkInitStruct.PLL2.PLL2N = 10;
  PeriphClkInitStruct.PLL2.PLL2P = 2;
  PeriphClkInitStruct.PLL2.PLL2Q = 2;
  PeriphClkInitStruct.PLL2.PLL2R = 2;
  PeriphClkInitStruct.PLL2.PLL2RGE = RCC_PLL2VCIRANGE_3;
  PeriphClkInitStruct.PLL2.PLL2VCOSEL = RCC_PLL2VCOMEDIUM;
  PeriphClkInitStruct.PLL2.PLL2FRACN = 0;
  PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL2;
  PeriphClkInitStruct.AdcClockSelection = RCC_ADCCLKSOURCE_PLL2;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief ADC3 Initialization Function
  *  None
  * @retval None
  */
static void MX_ADC3_Init(void)
{

  /* USER CODE BEGIN ADC3_Init 0 */

  /* USER CODE END ADC3_Init 0 */

  ADC_ChannelConfTypeDef sConfig = {0};

  /* USER CODE BEGIN ADC3_Init 1 */

  /* USER CODE END ADC3_Init 1 */

  /** Common config
  */
  hadc3.Instance = ADC3;
  hadc3.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV2;
  hadc3.Init.Resolution = ADC_RESOLUTION_16B;
  hadc3.Init.ScanConvMode = ADC_SCAN_DISABLE;
  hadc3.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
  hadc3.Init.LowPowerAutoWait = DISABLE;
  hadc3.Init.ContinuousConvMode = DISABLE;
  hadc3.Init.NbrOfConversion = 1;
  hadc3.Init.DiscontinuousConvMode = DISABLE;
  hadc3.Init.ExternalTrigConv = ADC_EXTERNALTRIG_T6_TRGO;
  hadc3.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;
  hadc3.Init.ConversionDataManagement = ADC_CONVERSIONDATA_DMA_CIRCULAR;
  hadc3.Init.Overrun = ADC_OVR_DATA_PRESERVED;
  hadc3.Init.LeftBitShift = ADC_LEFTBITSHIFT_NONE;
  hadc3.Init.OversamplingMode = DISABLE;
  hadc3.Init.Oversampling.Ratio = 1;
  if (HAL_ADC_Init(&hadc3) != HAL_OK)
  {
    Error_Handler();
  }

  /** Configure Regular Channel
  */
  sConfig.Channel = ADC_CHANNEL_9;
  sConfig.Rank = ADC_REGULAR_RANK_1;
  sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
  sConfig.SingleDiff = ADC_SINGLE_ENDED;
  sConfig.OffsetNumber = ADC_OFFSET_NONE;
  sConfig.Offset = 0;
  sConfig.OffsetSignedSaturation = DISABLE;
  if (HAL_ADC_ConfigChannel(&hadc3, &sConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN ADC3_Init 2 */

  /* USER CODE END ADC3_Init 2 */

}

/**
  * @brief SPI1 Initialization Function
  *  None
  * @retval None
  */
static void MX_SPI1_Init(void)
{

  /* USER CODE BEGIN SPI1_Init 0 */

  /* USER CODE END SPI1_Init 0 */

  /* USER CODE BEGIN SPI1_Init 1 */

  /* USER CODE END SPI1_Init 1 */
  /* SPI1 parameter configuration*/
  hspi1.Instance = SPI1;
  hspi1.Init.Mode = SPI_MODE_SLAVE;
  hspi1.Init.Direction = SPI_DIRECTION_2LINES;
  hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
  hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
  hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
  hspi1.Init.NSS = SPI_NSS_HARD_INPUT;
  hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
  hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
  hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
  hspi1.Init.CRCPolynomial = 0x0;
  hspi1.Init.NSSPMode = SPI_NSS_PULSE_DISABLE;
  hspi1.Init.NSSPolarity = SPI_NSS_POLARITY_LOW;
  hspi1.Init.FifoThreshold = SPI_FIFO_THRESHOLD_01DATA;
  hspi1.Init.TxCRCInitializationPattern = SPI_CRC_INITIALIZATION_ALL_ZERO_PATTERN;
  hspi1.Init.RxCRCInitializationPattern = SPI_CRC_INITIALIZATION_ALL_ZERO_PATTERN;
  hspi1.Init.MasterSSIdleness = SPI_MASTER_SS_IDLENESS_00CYCLE;
  hspi1.Init.MasterInterDataIdleness = SPI_MASTER_INTERDATA_IDLENESS_00CYCLE;
  hspi1.Init.MasterReceiverAutoSusp = SPI_MASTER_RX_AUTOSUSP_DISABLE;
  hspi1.Init.MasterKeepIOState = SPI_MASTER_KEEP_IO_STATE_DISABLE;
  hspi1.Init.IOSwap = SPI_IO_SWAP_DISABLE;
  if (HAL_SPI_Init(&hspi1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN SPI1_Init 2 */
  __HAL_SPI_DISABLE(&hspi1);
  MODIFY_REG(hspi1.Instance->CFG1, SPI_CFG1_FTHLV, SPI_FIFO_THRESHOLD_04DATA);
  __HAL_SPI_ENABLE(&hspi1);

  /* Enable SPI1 global interrupt so ErrorCallback can run */
  HAL_NVIC_SetPriority(SPI1_IRQn, 1, 0);
  HAL_NVIC_EnableIRQ(SPI1_IRQn);
  /* USER CODE END SPI1_Init 2 */

}

/**
  * @brief TIM6 Initialization Function
  *  None
  * @retval None
  */
static void MX_TIM6_Init(void)
{

  /* USER CODE BEGIN TIM6_Init 0 */

  /* USER CODE END TIM6_Init 0 */

  TIM_MasterConfigTypeDef sMasterConfig = {0};

  /* USER CODE BEGIN TIM6_Init 1 */

  /* USER CODE END TIM6_Init 1 */
  htim6.Instance = TIM6;
  htim6.Init.Prescaler = 99;
  htim6.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim6.Init.Period = 199;
  htim6.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim6) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_UPDATE;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim6, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM6_Init 2 */

  /* USER CODE END TIM6_Init 2 */

}

/**
  * @brief USART3 Initialization Function
  *  None
  * @retval None
  */
static void MX_USART3_UART_Init(void)
{

  /* USER CODE BEGIN USART3_Init 0 */

  /* USER CODE END USART3_Init 0 */

  /* USER CODE BEGIN USART3_Init 1 */

  /* USER CODE END USART3_Init 1 */
  huart3.Instance = USART3;
  huart3.Init.BaudRate = 115200;
  huart3.Init.WordLength = UART_WORDLENGTH_8B;
  huart3.Init.StopBits = UART_STOPBITS_1;
  huart3.Init.Parity = UART_PARITY_NONE;
  huart3.Init.Mode = UART_MODE_TX_RX;
  huart3.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart3.Init.OverSampling = UART_OVERSAMPLING_16;
  huart3.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart3.Init.ClockPrescaler = UART_PRESCALER_DIV1;
  huart3.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart3) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetTxFifoThreshold(&huart3, UART_TXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_SetRxFifoThreshold(&huart3, UART_RXFIFO_THRESHOLD_1_8) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_UARTEx_DisableFifoMode(&huart3) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART3_Init 2 */

  /* USER CODE END USART3_Init 2 */

}

/**
  * Enable DMA controller clock
  */
static void MX_BDMA_Init(void)
{

  /* DMA controller clock enable */
  __HAL_RCC_BDMA_CLK_ENABLE();

  /* DMA interrupt init */
  /* BDMA_Channel0_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(BDMA_Channel0_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(BDMA_Channel0_IRQn);

}

/**
  * Enable DMA controller clock
  */
static void MX_DMA_Init(void)
{

  /* DMA controller clock enable */
  __HAL_RCC_DMA1_CLK_ENABLE();

  /* DMA interrupt init */
  /* DMA1_Stream0_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(DMA1_Stream0_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(DMA1_Stream0_IRQn);

}

/**
  * @brief GPIO Initialization Function
  *  None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  /* USER CODE BEGIN MX_GPIO_Init_1 */

  /* USER CODE END MX_GPIO_Init_1 */

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOF_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();
  __HAL_RCC_GPIOD_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOB, GPIO_PIN_12, GPIO_PIN_RESET);

  /*Configure GPIO pin : PB12 */
  GPIO_InitStruct.Pin = GPIO_PIN_12;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

  /* USER CODE BEGIN MX_GPIO_Init_2 */

  /*  Configure SPI1 pins for very high speed*/
  GPIO_InitStruct.Pin = GPIO_PIN_4 | GPIO_PIN_5 | GPIO_PIN_6 | GPIO_PIN_7;  // NSS, SCK, MISO, MOSI
  GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /* USER CODE END MX_GPIO_Init_2 */
}

/* USER CODE BEGIN 4 */

/* printf over UART (blocking, thread context only)  */
static void uart_printf(const char *fmt, ...)
{
    char buf[256];
    va_list ap;
    va_start(ap, fmt);
    int n = vsnprintf(buf, sizeof(buf), fmt, ap);
    va_end(ap);
    if (n <= 0) return;

    /* Send with LF->CRLF conversion so terminal always sees CR+LF */
    for (int i = 0; i < n; ++i) {
        uint8_t c = (uint8_t)buf[i];
        if (c == '\n') {
            uint8_t cr = '\r';
            HAL_UART_Transmit(&UART_HANDLE, &cr, 1, HAL_MAX_DELAY);
        }
        HAL_UART_Transmit(&UART_HANDLE, &c, 1, HAL_MAX_DELAY);
    }
}

/* 4-byte SPI sample builder: [ADC_L, ADC_H, IDX_L, IDX_H] */
static void Build_SPI_Sample(uint8_t out[4], uint16_t adc_value, uint16_t sample_index)
{
    out[0] = (uint8_t)(adc_value & 0xFFu);
    out[1] = (uint8_t)((adc_value >> 8) & 0xFFu);
    out[2] = (uint8_t)(sample_index & 0xFFu);
    out[3] = (uint8_t)((sample_index >> 8) & 0xFFu);
}

/* Status-byte helper (bit0 valid, bit1 AC/DC, bit2 under, bit3 over) */
static inline uint8_t build_status_byte(void)
{
    uint8_t s = 0;
    s |= 1u;                                 /* bit0 = data valid / in-sync */
    s |= (signal_is_ac ? 1u : 0u) << 1;      /* bit1 = 1->AC, 0->DC         */
    if (win_min_raw < 10)     s |= (1u << 2);/* bit2 = underrange           */
    if (win_max_raw > 65525)  s |= (1u << 3);/* bit3 = overrange            */
    return s;
}

/* Compute mean/rms/min/max for a 240-sample block + AC/DC state  */
static void Process_Block(const uint16_t *p, uint32_t N)
{
    uint64_t acc = 0;
    uint16_t mn = 0xFFFFu, mx = 0x0000u;

    for (uint32_t i = 0; i < N; i++) {
        uint16_t s = p[i];
        acc += s;
        if (s < mn) mn = s;
        if (s > mx) mx = s;
    }
    uint32_t mean_raw = (uint32_t)(acc / N);

    long long acc_sq = 0;
    for (uint32_t i = 0; i < N; i++) {
        int32_t d = (int32_t)p[i] - (int32_t)mean_raw;
        acc_sq += (long long)d * (long long)d;
    }
    uint32_t rms_raw = (uint32_t)(sqrt((double)acc_sq / (double)N) + 0.5);

    /* publish RAW stats */
    win_mean_raw = mean_raw;
    win_rms_raw  = rms_raw;
    win_min_raw  = mn;
    win_max_raw  = mx;

    /* convert to mV for prints / thresholds */
    win_mean_mv = raw_to_mV(mean_raw);
    win_rms_mv  = raw_to_mV(rms_raw);
    win_min_mv  = raw_to_mV(mn);
    win_max_mv  = raw_to_mV(mx);

    /* hysteresis decision */
    static uint8_t ac_state = 0; /* 0=DC, 1=AC (persistent) */
    uint32_t p2p_mv = (win_max_mv >= win_min_mv) ? (win_max_mv - win_min_mv) : 0U;

    if (!ac_state) {
        if ((p2p_mv >= AC_P2P_HI_MV) && (win_rms_mv >= AC_RMS_HI_MV)) ac_state = 1;
    } else {
        if ((p2p_mv <= AC_P2P_LO_MV) && (win_rms_mv <= AC_RMS_LO_MV)) ac_state = 0;
    }
    signal_is_ac = ac_state;
}

/* ADC DMA CALLBACKS  */

void HAL_ADC_ConvHalfCpltCallback(ADC_HandleTypeDef *hadc)
{
    if (hadc->Instance != ADC3) return;

    pending_half  = 0;   /* first half [0..239] */
    stats_pending = 1;   /* tell main loop to process this half */
    shadow_valid  = 1;   /* we have valid data now */
}

void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef *hadc)
{
    if (hadc->Instance != ADC3) return;

    pending_half  = 1;   /* second half [240..479] */
    stats_pending = 1;   /* tell main loop to process this half */
    shadow_valid  = 1;
}

/* NOTE:
 * No SPI DMA helpers, no HAL_SPI_TxCpltCallback, and no HAL_SPI_ErrorCallback
 * anymore – we are using blocking HAL_SPI_Transmit() from the main loop instead.
 */

/* USER CODE END 4 */


 /* MPU Configuration */

void MPU_Config(void)
{
  MPU_Region_InitTypeDef MPU_InitStruct = {0};

  /* Disables the MPU */
  HAL_MPU_Disable();

  /** Initializes and configures the Region and the memory to be protected
  */
  MPU_InitStruct.Enable = MPU_REGION_ENABLE;
  MPU_InitStruct.Number = MPU_REGION_NUMBER0;
  MPU_InitStruct.BaseAddress = 0x0;
  MPU_InitStruct.Size = MPU_REGION_SIZE_4GB;
  MPU_InitStruct.SubRegionDisable = 0x87;
  MPU_InitStruct.TypeExtField = MPU_TEX_LEVEL0;
  MPU_InitStruct.AccessPermission = MPU_REGION_NO_ACCESS;
  MPU_InitStruct.DisableExec = MPU_INSTRUCTION_ACCESS_DISABLE;
  MPU_InitStruct.IsShareable = MPU_ACCESS_SHAREABLE;
  MPU_InitStruct.IsCacheable = MPU_ACCESS_NOT_CACHEABLE;
  MPU_InitStruct.IsBufferable = MPU_ACCESS_NOT_BUFFERABLE;

  HAL_MPU_ConfigRegion(&MPU_InitStruct);
  /* Enables the MPU */
  HAL_MPU_Enable(MPU_PRIVILEGED_DEFAULT);

}

/**
  * @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.
  *   file: pointer to the source file name
  *   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 */

The SPI pins are configured as follows: PB4 = NSS, PA5 = SCK, PA6 = MISO, PB5 = MOSI. SPI mode is CPOL = 0, CPHA = 1, 8-bit data size, FIFO threshold set to 4 bytes, and DMA is enabled for SPI1_TX. The program runs, the ADC works, callbacks fire, and DMA TX is continuously restarted, but the external master always receives 0xFF 0xFF 0xFF 0xFF regardless of the actual ADC data. I need help understanding why SPI slave DMA never outputs my prepared 4-byte buffer on MISO even though DMA callbacks indicate transfers are happening. Why does SPI slave output remains 0xFF not ADC values?

Any guidance or corrections to my configuration/code would be greatly appreciated.

Thank you.

gbm · ‎2025-12-11

1. Check the address of spi_yx buffer in .map file. I won't be surprised if it's placed in Flash or some other strange place.

2 SPI slave is not an easy thing to implement. You must guarantee that the data is ready and DMA transfer is setup before the master starts SPI transfer.

My STM32 stuff on github - compact USB device stack and more: https://github.com/gbm-ii/gbmUSBdevice