Can the STM32H743's FMC drive a 16-bit 8080 bus faster than 1.6MHz when clocked at 480MHz?

Question

I'm using the FMC of the STM32H743 to drive a 16-bit 8080-bus LCD controller.

I've tried using DMA, MDMA and a CPU-loop to transfer data to the 8080-bus, via the FMC.

The transfer frequency does not depend on whether DMA, MDMA or CPU-loop is used. This make me think that the DMA/MDMA/CPU-loop is not the limiting factor.

At a 480MHz FMC clock, the transfer happens at just 1.6MHz, giving me only 20fps on a 16-bit colour 320x240 LCD.

At a 240MHz FMC clock, the transfer happens at just 0.8MHz, and so on at slower speeds.

I've also tried reducing the various setup and hold times to 1 and 0 cycles, but this has (surprisingly) not affected the waveform on the 8080-bus.

My (Cube-MX generated) FMC initialisation code is:

/* FMC initialization function */
static void MX_FMC_Init(void)
{

  /* USER CODE BEGIN FMC_Init 0 */

  /* USER CODE END FMC_Init 0 */

  FMC_NORSRAM_TimingTypeDef Timing = {0};
  FMC_NORSRAM_TimingTypeDef ExtTiming = {0};

  /* USER CODE BEGIN FMC_Init 1 */

  /* USER CODE END FMC_Init 1 */

  /** Perform the SRAM1 memory initialization sequence
  */
  hsram1.Instance = FMC_NORSRAM_DEVICE;
  hsram1.Extended = FMC_NORSRAM_EXTENDED_DEVICE;
  /* hsram1.Init */
  hsram1.Init.NSBank = FMC_NORSRAM_BANK2;
  hsram1.Init.DataAddressMux = FMC_DATA_ADDRESS_MUX_DISABLE;
  hsram1.Init.MemoryType = FMC_MEMORY_TYPE_SRAM;
  hsram1.Init.MemoryDataWidth = FMC_NORSRAM_MEM_BUS_WIDTH_16;
  hsram1.Init.BurstAccessMode = FMC_BURST_ACCESS_MODE_DISABLE;
  hsram1.Init.WaitSignalPolarity = FMC_WAIT_SIGNAL_POLARITY_LOW;
  hsram1.Init.WaitSignalActive = FMC_WAIT_TIMING_BEFORE_WS;
  hsram1.Init.WriteOperation = FMC_WRITE_OPERATION_ENABLE;
  hsram1.Init.WaitSignal = FMC_WAIT_SIGNAL_DISABLE;
  hsram1.Init.ExtendedMode = FMC_EXTENDED_MODE_ENABLE;
  hsram1.Init.AsynchronousWait = FMC_ASYNCHRONOUS_WAIT_DISABLE;
  hsram1.Init.WriteBurst = FMC_WRITE_BURST_DISABLE;
  hsram1.Init.ContinuousClock = FMC_CONTINUOUS_CLOCK_SYNC_ONLY;
  hsram1.Init.WriteFifo = FMC_WRITE_FIFO_DISABLE;
  hsram1.Init.PageSize = FMC_PAGE_SIZE_NONE;
  /* Timing */
  Timing.AddressSetupTime = 3;
  Timing.AddressHoldTime = 15;
  Timing.DataSetupTime = 4;
  Timing.BusTurnAroundDuration = 1;
  Timing.CLKDivision = 16;
  Timing.DataLatency = 17;
  Timing.AccessMode = FMC_ACCESS_MODE_A;
  /* ExtTiming */
  ExtTiming.AddressSetupTime = 3;
  ExtTiming.AddressHoldTime = 15;
  ExtTiming.DataSetupTime = 4;
  ExtTiming.BusTurnAroundDuration = 1;
  ExtTiming.CLKDivision = 16;
  ExtTiming.DataLatency = 17;
  ExtTiming.AccessMode = FMC_ACCESS_MODE_A;

  if (HAL_SRAM_Init(&hsram1, &Timing, &ExtTiming) != HAL_OK)
  {
    Error_Handler( );
  }

  HAL_SetFMCMemorySwappingConfig(FMC_SWAPBMAP_SDRAM_SRAM);
}

My amended settings were:

  Timing.AddressSetupTime = 1;
  Timing.AddressHoldTime = 1;
  Timing.DataSetupTime = 1;
  Timing.BusTurnAroundDuration = 1; // not needed
  Timing.CLKDivision = 1; // not needed
  Timing.DataLatency = 34;
  Timing.AccessMode = FMC_ACCESS_MODE_A;
  ExtTiming.AddressSetupTime = 1;
  ExtTiming.AddressHoldTime = 1;
  ExtTiming.DataSetupTime = 1;
  ExtTiming.BusTurnAroundDuration = 1;  // not needed
  ExtTiming.CLKDivision = 1; // not needed
  ExtTiming.DataLatency = 34;
  ExtTiming.AccessMode = FMC_ACCESS_MODE_A;

and

  Timing.AddressSetupTime = 0;
  Timing.AddressHoldTime = 0;
  Timing.DataSetupTime = 0;
  Timing.BusTurnAroundDuration = 0; // not needed
  Timing.CLKDivision = 1; // not needed
  Timing.DataLatency = 0;
  Timing.AccessMode = FMC_ACCESS_MODE_A;
  ExtTiming.AddressSetupTime = 0;
  ExtTiming.AddressHoldTime = 0;
  ExtTiming.DataSetupTime = 0;
  ExtTiming.BusTurnAroundDuration = 0;  // not needed
  ExtTiming.CLKDivision = 1; // not needed
  ExtTiming.DataLatency = 34;
  ExtTiming.AccessMode = FMC_ACCESS_MODE_A;

The (Cube-MX generated) clock setup is:

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {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_SCALE0);

  while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}
  /** Macro to configure the PLL clock source 
  */
  __HAL_RCC_PLL_PLLSOURCE_CONFIG(RCC_PLLSOURCE_HSE);
  /** Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_BYPASS;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 4;
  RCC_OscInitStruct.PLL.PLLN = 480;
  RCC_OscInitStruct.PLL.PLLP = 2;
  RCC_OscInitStruct.PLL.PLLQ = 20;
  RCC_OscInitStruct.PLL.PLLR = 2;
  RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_1;
  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 busses 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_DIV2;
  RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
  RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
  {
    Error_Handler();
  }
  PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI1|RCC_PERIPHCLK_USB
                              |RCC_PERIPHCLK_QSPI|RCC_PERIPHCLK_FMC;
  PeriphClkInitStruct.PLL2.PLL2M = 2;
  PeriphClkInitStruct.PLL2.PLL2N = 120;
  PeriphClkInitStruct.PLL2.PLL2P = 8;
  PeriphClkInitStruct.PLL2.PLL2Q = 2;
  PeriphClkInitStruct.PLL2.PLL2R = 1;
  PeriphClkInitStruct.PLL2.PLL2RGE = RCC_PLL2VCIRANGE_2;
  PeriphClkInitStruct.PLL2.PLL2VCOSEL = RCC_PLL2VCOWIDE;
  PeriphClkInitStruct.PLL2.PLL2FRACN = 0;
  PeriphClkInitStruct.FmcClockSelection = RCC_FMCCLKSOURCE_PLL2;
  PeriphClkInitStruct.QspiClockSelection = RCC_QSPICLKSOURCE_D1HCLK;
  PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL;
  PeriphClkInitStruct.UsbClockSelection = RCC_USBCLKSOURCE_PLL;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Enable USB Voltage detector 
  */
  HAL_PWREx_EnableUSBVoltageDetector();
}

How can I make the FMC on the STM32H743 transfer half-words faster than 1.6MHz, when driven with a 480MHz clock?

Answer 1

To make the FMC run fast, you must configure the bank that you are going to use.

I had mistakenly configured NE2 bank and then used the address which corresponded to the NE1 bank.

Full details: https://community.st.com/s/question/0D50X0000CAuyJ7SQJ/can-the-stm32h743s-fmc-drive-a-16bit-8080-bus-faster-than-16mhz-when-clocked-at-480mhz