how to send many float from stm32f103 to PC through UART?

Question

I want my PC to receive float value from the microcontroller so as to plot graph based on the value. I already can let microcontroller to receive value from PC. I am using union decode the float into bytes.

My union in both microcontroller and PC socket(I connect my PC to microcontroller through bluetooth, HC-06 and use HC-06 to connect to my stm32f103 through uart)

union
{
    float data;
    struct
    {
        uint8_t bytes[4];
    };
}Float[250];

How I transmit bytes from STM32F103 to PC: I first put my value in an array and then put the elements inside the union bytes before sending. (The value is keep updating, I tried to send the whole array before but seems failed).

for(int i = 0; i < 250; i++)
        {
            Float[i].F = data[i];
        }

        for(int i = 0; i < 250; i++)
        {
            for(int j = 0; j < 4; j++)
            {
                HAL_UART_Transmit(&huart1, (uint8_t* )&Float[i].bytes[j], 1, HAL_MAX_DELAY);

                while(USART1->SR != USART_SR_TC){};
            }
        }
        HAL_UART_Transmit(&huart2, (uint8_t*)"Transmitted to PC\n", 18, HAL_MAX_DELAY);

        value = 0;
        memset(data, 0, 250);
        counter = 0;

In my PC, i receive the data through rfcomm

status = recv(s, buffer, 1000, 0);

Then decode the bytes into floats:

for(int i = 0; i < 250; i++)
    {
        for(int j = 0; j < 4; j++)
        {
            Float[i].bytes[j] = buffer[j + rcv_counter];
        }
        rcv_counter += 4;
        
    }

However, when i received the bytes send from microcontroller and decode them, i got all zero... I am not sure what is the reason. I also glad people provide some other way to do this. . My main goal is just to transmit float values from microconttroller to PC through uart. Thx very much.

Just to update my progress:

Now I can receive true float value from stm32f103 only once, if I continue requesting stm32f103 to send value, it will send only zero, I not so sure why is this happening.

float test[5] = {1.0, 5.6, 4.5, 2.3, 8.9}; // float value to be send
HAL_UART_Transmit(&huart1, (uint8_t* )test, sizeof(test), HAL_MAX_DELAY); // Transmit from stm32f103 to PC

union
{
    float data;
    struct
    {
        uint8_t bytes[4];
    };
}Float[5]; // Union to decode bytes

if(recv(s, buffer, 20, 0) >= 0)
            {
                cout << "Message received from bluepill" << endl;
          

                for(int i = 0; i < 5; i++)
                {
                    for(int j = 0; j < 4; j++)
                    {
                        Float[i].bytes[j] = buffer[j + rcv_counter];
                    }
                    rcv_counter += 4;
                    
                }
                for(int i = 0; i < 5; i++)
                {
                    cout << Float[i].data << endl;
                }
            } // Way to receive 5 float value and print to console

When i try this, i can only success one time, start from second time, i keep receiving 0, thx for helping

Can you successfully send a string and receive it on the PC? — Codo, Mar 12 '22 at 10:10
Most of the code on the microcontroller is not needed. You can simply call `HAL_UART_Transmit(&huart1, data, sizeof(data), HAL_MAX_DELAY);` (assuming `data` is an array of `float`). — Codo, Mar 12 '22 at 10:12
seems i can only receive the valid value once... when i receive the value second time, i got rubbish value — wps, Mar 12 '22 at 15:59
Sending multi-byte binary values without any message framing is doomed to eventually lose proper alignment. E.G. see https://stackoverflow.com/questions/16177947/identification-of-packets-in-a-byte-stream/16180135#16180135 — sawdust, Mar 13 '22 at 02:42

score 0 · Answer 1 · answered Mar 23 '22 at 20:06

Create a TX-Buffer:

#define TXBUFSIZE nn
#define FARRAYSIZE mm
uint8_t TXBuffer[TXBUFSIZE] = {0};
float myArray[FARRAYSIZE] = {0,};

where nn is the number of bytes you need to send. If you want to send 250 float values in one package this would be 250 * sizeof(float)

fill the buffer in a while loop:

uint16_t size = FARRAYSIZE * sizeof(float);
uint16_t i = size;  
uint8_t *pSrc = (uint8_t*)myArray;
uint8_t *pDst = TXBuffer;

while(i--) *pDst++ = *pSrc++;

HAL_UART_Transmit(&huart2, TXBuffer, size, HAL_MAX_DELAY);

or you could simply typecast the float array into a byte array and send it out:

uint16_t size = FARRAYSIZE * sizeof(float);
uint8_t* pSrc = (uint8_t*)myArray;
HAL_UART_Transmit(&huart2, TXBuffer, size, HAL_MAX_DELAY);

Then you could omit the creation of a separate TxBuffer and save memory usage. Alas my recommendation would be to use HAL_UART_Transmit_DMA(...) for such long byte streams. In this case I'd strongly recommend to use a separate TX buffer, because then you can change the values in the original float array, while the DMA uses the TX Buffer to send out your data.

how to send many float from stm32f103 to PC through UART?

1 Answers1