HAL_UART Transmit/Receive dont work when not using a fixed size as parameter?

[BMo.1]

in my program is receive first data that tells me what's the size of the payload i am getting next through UART ,When i use that variable as parameter in the UART functions it doesnt work ,however when i hard code a value say HAL_Uart_Receive(&huart1,buffer,5,...) it does indeed work.

Here is my code

#define Max_Buffer_Size		16384UL
uint8_t buffer[Max_Buffer_Size];
 
HAL_UART_Receive(&huart1,buffer,1,HAL_MAX_DELAY);
int payload_length =buffer[0];
HAL_UART_Receive(&huart1,buffer,payload_length,HAL_MAX_DELAY);

as i said if replace line 6 with this is it works :

HAL_UART_Receive(&huart1,buffer,5,HAL_MAX_DELAY);

Thank you for your help.

[waclawek.jan]

Or just drop Cube/HAL and write your own blocking UART receiver. It's literally 5 lines of code.

JW

[ONadr.1]

So, try to blink LED when buffer[0] is equal 5. You probably dont receive what you expected.

[BMo.1]

So I tried to implement my own Receive function like this :

void Serial_Receive(uint8_t* buffer ,uint8_t size){
	int i=0 ;
	while(i < size ){
		while (!(USART1->SR & USART_SR_RXNE));
		buffer[i]=USART1->DR;
		i++;	
	}
}

When i call it with payload_length as a parameter it blocks exactly like the HAL fucntion

		Serial_Receive(buffer2,payload_length);

A call with a hard coded value proceeds smoothly and the program continues its execution.

Serial_Receive(buffer2,5);

The problem probably lies with payload_length variable and I don't see why honestly.

[S.Ma]

I would use DMA in polling modr. Use a cyclic mode over 16 bytes buffer, that is simpler.... and is non blocking...

[waclawek.jan]

What exactly does the transmitter transmit? Is it

05 xx xx xx xx

or

05 xx xx xx xx xx

?

JW

[BMo.1]

Okay will try it.

I just want to understand what's the problem in this case tbh.

[BMo.1]

first he transmits 5 and then transmits a 5byte string lets say "Hello".

[waclawek.jan]

Okay, and what is the result of something like

if (payload_length == 5)

LED_ON();

else

LED_OFF();

?

You should consider using a working environment which enables the nowadays usual debugging facilities (breakpoints, single-stepping, observing memories/variables etc.)

JW

[TDK]

Probably payload_length isn't what you think it is. What other explanation could there be? The variable is passed by value. The function itself has no idea if you passed a literal or a variable.

[BMo.1]

Led doesn't turn on payload_length is the problem.Also i test buffer[0] instead of payload_length,LED doesn't turn on.

I am not getting the data i expect i guess ?

Also can't really debug because i use those chinese st-link clone to flash and then and FTDI chip to test the uart communication.Can't have both at the same time.