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STM32F4xx HAL UART BAUD Timing Issues

dj
Associate II
Posted on January 24, 2015 at 19:54

Hi there... Using the non-hal on an STM32F2xx, I can read/write at 3,333,333 BAUD without a problem. When I port the code to STM32F4xx, I am unable to read/write to the USART1 at the same BAUD rate - instead, it times out.

If I change the baud rate to 4,300,000 - it works. If I change it back to 3,333,333 - it doesn't work. Does anyone have an idea of why this could be happening? Here is my non-working code...

UART_HandleTypeDef huart1; 
int main(void) { 
HAL_Init(); 
__GPIOA_CLK_ENABLE(); 
__GPIOB_CLK_ENABLE(); 
__GPIOC_CLK_ENABLE(); 
GPIO_InitTypeDef GPIO_InitStruct; 
// --------------------------------------------------------------------------- LED 
GPIO_InitStruct.Pin = GPIO_PIN_15; 
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP; 
GPIO_InitStruct.Speed = GPIO_SPEED_HIGH; 
GPIO_InitStruct.Pull = GPIO_NOPULL; 
HAL_GPIO_Init(GPIOC, &GPIO_InitStruct); 
// --------------------------------------------------------------------------- USART 1 
/**USART1 GPIO Configuration 
PA9 ------> USART1_TX 
PA10 ------> USART1_RX 
PA11 ------> USART1_CTS 
PA12 ------> USART1_RTS 
*/ 
__USART1_CLK_ENABLE(); 
GPIO_InitStruct.Pin = GPIO_PIN_9 | GPIO_PIN_10; 
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP; 
GPIO_InitStruct.Pull = GPIO_PULLUP; 
GPIO_InitStruct.Speed = GPIO_SPEED_HIGH; 
GPIO_InitStruct.Alternate = GPIO_AF7_USART1; 
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct); 
GPIO_InitStruct.Pin = GPIO_PIN_11 | GPIO_PIN_12; 
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP; 
GPIO_InitStruct.Pull = GPIO_NOPULL; 
GPIO_InitStruct.Speed = GPIO_SPEED_HIGH; 
GPIO_InitStruct.Alternate = GPIO_AF7_USART1; 
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct); 
huart1.Instance = USART1; 
huart1.Init.BaudRate = 3333333; 
huart1.Init.WordLength = UART_WORDLENGTH_8B; 
huart1.Init.StopBits = UART_STOPBITS_1; 
huart1.Init.Parity = UART_PARITY_NONE; 
huart1.Init.Mode = UART_MODE_TX_RX; 
huart1.Init.HwFlowCtl = UART_HWCONTROL_RTS_CTS; 
huart1.Init.OverSampling = UART_OVERSAMPLING_8; 
HAL_UART_Init(&huart1); 
// --------------------------------------------------------------------------- 
for (;;) { 
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_15, GPIO_PIN_SET); 
HAL_Delay(250); 
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_15, GPIO_PIN_RESET); 
HAL_Delay(250); 
HAL_UART_Transmit(&huart1, (uint8_t *)&''Hello'', 5, 1000); 
} 
} 

#uart-usart-stm32f4xx-baud
1 REPLY 1
Posted on January 25, 2015 at 15:44

Does the problem manifest if you run the STM32F4 at 120 MHz?

The USART at high baud rates is going to be impacted by the APB speed, whether that's 60, 84 or 90 MHz in this case.

Other than that you'll have to wade through the source, and look at the USART/BRR registers, etc.
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