Registering a User callback for USART on STM32L4S5ZI

[SJant.1]

Hi,

I have got confused in knowing how to actually register a User call back function for Transfer complete event in UART. I am using DMA.

To give an idea on what I am doing, below re the lines that I have added in my code.

void TxComplete_Callback(struct __UART_HandleTypeDef *huart); //declaration of user callback fun
 
huart1.TxCpltCallback =  TxComplete_Callback; // assigning it to transfer complete event callback of the uart instance
 
void TxComplete_Callback(struct __UART_HandleTypeDef *huart) {
 
 }   // function definition which is currently not full

My question is whether the argument for the callback function has to be compulsorily (struct __UART_HandleTypeDef *huart)? because in UART_DMATransmitCplt() function it knows that the event received is DMA Transfer Complete and so it checks if huart->TxCpltCallback is populated or else it executes the weak function as can be see below

#if (USE_HAL_UART_REGISTER_CALLBACKS == 1)
    /*Call registered Tx complete callback*/
    huart->TxCpltCallback(huart);
#else
    /*Call legacy weak Tx complete callback*/
    HAL_UART_TxCpltCallback(huart);
#endif /* USE_HAL_UART_REGISTER_CALLBACKS */

So the doubt I have is if this is how a callback function can be assigned, then what does the HAL_UART_RegisterCallback() function help me to do?

And will the changes that I have made work and whenever the DMA transfer complete event occurs, my custom function TxComplete_Callback will be called and executed? Can I similarly add a RxComplete_Callback function?

Please help me in these confusions. I have set USE_HAL_UART_REGISTER_CALLBACKS to 1 to enable the callbacks.

Thanks!!

[Amel NASRI · Accepted solution]

Hi @SJant.1​ ,

A complete explanation with examples is provided by @Tilen MAJERLE​  in this Github article.

-Amel

[SJant.1]

Thanks Amel!

[SJant.1]

Hi Amel,

I found the Github article quite informative. I found an answer for the same.

I have a new question now, and if you can throw some light on it, it would be really helpful.

In my application, I am using DMA to transfer and receive data to a serial terminal which we are using as a debug-shell. The challenge I am facing is, in the UART_READ function, I am using HAL_UART_Receive_DMA function. the user provides the length of data to be read, but I have to internally read the Rx data byte by byte strictly. Hence even though I know the length of data to be read, I cannot use that length in the HAL_UART_Receive_DMA() function and compulsorily use sizeof(char). I am using a receive complete callback and everytime a char is read, the callback function is executed and in that I am not sure what should I actually put in. should I call the receive function again? Even if I do that and if the user enters a string for example "hello", then won't some of the characters be overwritten in RDR register before they are actually read?

I you have any idea on how this situation can be handled, please let me know.

Thanks!!

[Piranha]

Tilen's article is great, but it's not an explanation of HAL library. Actually it's the exact opposite - it shows how to drop the unusable broken HAL bloatware and make a working USART implementation.