Time diference betwen using ST libraries and uControler registers directly

tecnico23 · ‎2014-03-13

Posted on March 13, 2014 at 11:55

Hi

I'm using STLibraries for programing a STM32F100 in crossStudio. I have my System Clock with 24MHz.

When I set and reset a port pin, using LT Libraries

while(1){

GPIO_SetBits(DISP_DIGIT1_PORT, DISP_DIGIT1_PIN);

GPIO_ResetBits(DISP_DIGIT1_PORT,DISP_DIGIT1_PIN);

}

since the moment of set to the moment of reset the uController spend, more or less, 2.26us (442KHz). On the other hand, if I do the same using the uController register

while(1){

DISP_DIGIT1_PORT->BSRR = DISP_DIGIT1_PIN;

DISP_DIGIT1_PORT->BRR = DISP_DIGIT1_PIN;

}

the this time is only 164ns (6.1MHz).

So, my questions are : This diferences on time is normal? There are any solucion for using LTLibraries and reduce this time?

Best Regards

A Paiva

waclawek.jan · ‎2014-03-13

Posted on March 13, 2014 at 12:07

> This diferences on time is normal?

Look at the generated assembler. The first one probably results in function calls, the second is probably inlined as one or few instructions.

> There are any solucion for using LTLibraries and reduce this time?

Switch on optimizations.

JW