Uart Report Freezes With Continuous Data

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How To Receive UART Serial Data With STM32 – DMA / Interrupt / Polling
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STM32 UART Receive DMA Interrup Example HAL Code

In this tutorial, I'll briefly list down the different ways to receive UART data in STM32 microcontrollers. Starting with the least efficient way which is polling for the UART peripheral received data, then we'll see the interrupt-driven reception method which involves the CPU intervention but it's non-blocking anyway. And lastly, and most importantly, the DMA UART receive method which doesn't require any CPU intervention at all and can be considered the most efficient way to achieve this task.

Required Components For LABs

All the example code/LABs/projects in the course are going to be done using those boards below.

Nucleo32-L432KC (ARM Cortex-M4 @ 80MHz) or (eBay)
Blue Pill STM32-F103 (ARM Cortex-M3 @ 72MHz) or (eBay)
ST-Link v2 Debugger or (eBay)

QTY	Component Name	🛒 Amazon.com	🛒 eBay.com
2	BreadBoard	Amazon	eBay
1	LEDs Kit	Amazon Amazon	eBay
1	Resistors Kit	Amazon Amazon	eBay
1	Capacitors Kit	Amazon Amazon	eBay & eBay
2	Jumper Wires Pack	Amazon Amazon	eBay & eBay
1	9v Battery or DC Power Supply	Amazon Amazon Amazon	eBay
1	Micro USB Cable	Amazon	eBay
1	Push Buttons	Amazon Amazon	eBay
1	USB-TTL Converter or FTDI Chip	Amazon Amazon	eBay eBay

★ Check The Full Course Complete Kit List

Some Extremely Useful Test Equipment For Troubleshooting:

My Digital Storage Oscilloscope (DSO): Siglent SDS1104 (on Amazon.com) (on eBay)
FeelTech DDS Function Generator: KKMoon FY6900 (on Amazon.com) (on eBay)
Logic Analyzer (on Amazon.com) (on eBay)

Affiliate Disclosure: When you click on links in this section and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network (EPN) and Amazon.com.

STM32 UART Receive

This tutorial is intended to be an example application for the DMA unit which we've discussed in the previous tutorial (DMA Tutorial). However, I'd like also to list down all the other possible ways in order to receive serial UART data with an STM32 microcontroller including the DMA method.

1 The Polling Method

The polling method is essentially a blocking function being called from the main routine and it does block the CPU so it can't proceed in the main task execution until a certain amount of UART data bytes are received. After receiving the required amount of data, the function ends and the CPU continues the main code execution. Otherwise, and if the UART peripheral for some reason didn't receive the expected amount of data, the function will keep blocking the CPU for a certain amount of time "time-out" after which it gets terminated and gives back the control to the CPU to resume the main code.

This function for example

HAL_UART_Receive ( & huart1 , UART1_rxBuffer , 12 , 5000 ) ;

Receives 12 bytes to the buffer. if it does that in 100uSec, it's ok and the CPU will resume main code execution. If it doesn't receive that amount of data, the CPU will be kept blocked waiting for 5sec until this function returns to the main context. And obviously, it's not an efficient way to receive serial data despite the fact that it does actually work.

2 The Interrupt Method

Using interrupt signals is a convenient way to achieve serial UART data reception. The CPU initializes the UART receive hardware so that it fires an interrupt signal whenever a new byte of data is received. And in the ISR code, we save the received data in a buffer for further processing.

This way of handling the UART data reception is a non-blocking way. As the CPU initiates the receiving process and it resumes executing the main code. Until an interrupt is received, then it freezes the main context and switches to the ISR handler to save the received byte to a buffer and switches back to the main context and resume the main code.

HAL_UART_Receive_IT ( & huart1 , UART1_rxBuffer , 12 ) ;

The above function initializes the UART receive process in interrupt mode (non-blocking) and upon completion, a callback function is called to notify the application and the processor knows that the received data buffer is now ready.

This method is a non-blocking one, yet very efficient. However, if you're receiving a continuous stream of serial data, an insane number of interrupts per second will have to be handled by the CPU which is a huge loading and a waste of time for it. In this situation, even the interrupt method will be inefficient and unnecessarily loading the CPU and consuming too much of the CPU time. And in worst scenarios, there might be some data packets lost or dropped in the way. Now, it comes the time to use the DMA method.

3 The DMA Method

Using the DMA unit in order to direct the received serial UART data from the UART peripheral directly to the memory is considered to be the most efficient way to do such a task. It requires no CPU intervention at all, you'll have only to set it up and go execute the main application code. The DMA will notify back the CPU upon reception completion and that received data buffer will be in the pre-programmed location.

The DMA can prioritize the channels, decide on the data width, and also the amount of data to be transferred up to 65536 bytes. Which is amazing in fact, and all you've got to do is to initialize it like this.

HAL_UART_Receive_DMA ( & huart1 , UART1_rxBuffer , 12 ) ;

In the following sections, we'll create a simple STM32 UART receive examples using each of the 3 methods.

STM32 UART Receive LAB Brief

LAB Number	18
LAB Title	STM32 UART Receive LAB (3 Methods Applications)

Application1: Setup UART receive system using the polling method
Application2: Setup UART receive system using the interrupt method
Application3: Setup UART receive system using the DMA method

Each application will have to receive 12 bytes of data from the PC terminal and echo back the received data buffer. So in the testing, we'll expect to see back whatever data we send through the terminal.

STM32 UART Receive Polling Example

Start New CubeMX Project & Setup The Clock

Setup The UART1 Peripheral in Async Mode @ 9600bps

STM32 UART Receive DMA Interrupt Polling Example Tutorial

Generate Code & Open CubeIDE or Any Other IDE You're Using

Write This Application Code (main.c)

#include "main.h"

uint8_t UART1_rxBuffer [ 12 ] = { 0 } ;

UART_HandleTypeDef huart1 ;

void SystemClock_Config ( void ) ;

static void MX_GPIO_Init ( void ) ;

static void MX_USART1_UART_Init ( void ) ;

int main ( void )

{

HAL_Init ( ) ;

SystemClock_Config ( ) ;

MX_GPIO_Init ( ) ;

MX_USART1_UART_Init ( ) ;

HAL_UART_Receive ( & huart1 , UART1_rxBuffer , 12 , 5000 ) ;

HAL_UART_Transmit ( & huart1 , UART1_rxBuffer , 12 , 100 ) ;

while ( 1 )

{

}

Testing Result On The TeraTerm Terminal

STM32 UART Receive DMA Interrupt Polling Example

STM32 UART Recieve Interrupt Example

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Start New CubeMX Project & Setup The Clock

Setup The UART1 Peripheral in Async Mode @ 9600bps

STM32 UART Receive DMA Interrupt Polling Example Tutorial

Enable The UART1 Global Interrupt From NVIC Controller Tab

STM32 UART Receive DMA Interrupt Polling Example Tutorial With Code

Generate Code & Open CubeIDE or Any Other IDE You're Using

Write This Application Code (main.c)

#include "main.h"

uint8_t UART1_rxBuffer [ 12 ] = { 0 } ;

UART_HandleTypeDef huart1 ;

void SystemClock_Config ( void ) ;

static void MX_GPIO_Init ( void ) ;

static void MX_USART1_UART_Init ( void ) ;

int main ( void )

{

HAL_Init ( ) ;

SystemClock_Config ( ) ;

MX_GPIO_Init ( ) ;

MX_USART1_UART_Init ( ) ;

HAL_UART_Receive_IT ( & huart1 , UART1_rxBuffer , 12 ) ;

while ( 1 )

{

}

void HAL_UART_RxCpltCallback ( UART_HandleTypeDef * huart )

{

HAL_UART_Transmit ( & huart1 , UART1_rxBuffer , 12 , 100 ) ;

HAL_UART_Receive_IT ( & huart1 , UART1_rxBuffer , 12 ) ;

}

Testing Result On The TeraTerm Terminal

STM32 UART Receive DMA Interrupt Polling Example Code

STM32 UART Receive DMA Example

Start New CubeMX Project & Setup The Clock

Setup The UART1 Peripheral in Async Mode @ 9600bps

STM32 UART Receive DMA Interrupt Polling Example Tutorial

Add A DMA Channel For UART RX From The DMA Tab

STM32 UART Receive DMA HAL Example With Code

Generate Code & Open CubeIDE or Any Other IDE You're Using

Write This Application Code (main.c)

#include "main.h"

uint8_t UART1_rxBuffer [ 12 ] = { 0 } ;

UART_HandleTypeDef huart1 ;

DMA_HandleTypeDef hdma_usart1_rx ;

void SystemClock_Config ( void ) ;

static void MX_GPIO_Init ( void ) ;

static void MX_DMA_Init ( void ) ;

static void MX_USART1_UART_Init ( void ) ;

int main ( void )

{

HAL_Init ( ) ;

SystemClock_Config ( ) ;

MX_GPIO_Init ( ) ;

MX_DMA_Init ( ) ;

MX_USART1_UART_Init ( ) ;

HAL_UART_Receive_DMA ( & huart1 , UART1_rxBuffer , 12 ) ;

while ( 1 )

{

}

void HAL_UART_RxCpltCallback ( UART_HandleTypeDef * huart )

{

HAL_UART_Transmit ( & huart1 , UART1_rxBuffer , 12 , 100 ) ;

HAL_UART_Receive_DMA ( & huart1 , UART1_rxBuffer , 12 ) ;

}

Testing Result On The TeraTerm Terminal

STM32 UART Receive DMA HAL Example With Code CubeMX

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Source: https://deepbluembedded.com/how-to-receive-uart-serial-data-with-stm32-dma-interrupt-polling/

Uart Report Freezes With Continuous Data

Required Components For LABs

STM32 UART Receive

STM32 UART Receive LAB Brief

STM32 UART Receive Polling Example

STM32 UART Recieve Interrupt Example

STM32 UART Receive DMA Example

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