Problem with "HAL_UART_Transmit_IT" function

[SDall.11]

Hi, I've a problem with function HAL_UART_Transmit_IT.

If I call this function with global data array, there isn't a problem, but If I call it with a non global data array, I receive wrong data.

This is a sample code:

void SendData()
{
    uint8_t s[10];
    memset(&s, 0x10, 10);
    HAL_UART_Transmit_IT(&huart2, &s[0], sizeof(s));
}

This example gives problems, but if I move "uint8_t s[10]" out of function (make global) all works fine.

I don't understand the problem :(

I'm using IAR.

Some idea?

Thanks.

[prain]

In c programming language​, you should consider variable "scopes". memory used by variables inside functions, will automatically free after you exit the function. The temporary memory space that holds such variables is called stack.

[Piranha]

It's a stack, not a heap...

[SDall.11]

You're right, but...

when I call HAL_UART_Transmit_IT the function is still alive.

SendData die when HAL_UART_Transmit_IT returns.

But now, answering you I've a doubt.

I think that HAL_UART... returns before to have effectively sent data?

Tomorrow I make some tests.

Thanks for help.

[prain]

Yes, correct​

[prain]

HAL_UART_Transmit_IT doesn't wait for transmit completion. It transmit data in background and call you back when transfer complete.

[Yevgeni Tunik]

HAL_UART_Transmit_IT() starts the transmit and exits. The auto variable s[10] will be out of the scope. Its stack allocated memory can be overwritten by any other function. To fix the issue, you can declare s[10] as static, or insert enough delay after HAL_UART_Transmit_IT().

[E-John]

I've had that same problem.

My solution is to declare the transmitted buffer as "global" or "static" type.