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Sterling

•Created by Sterling on 7/30/2024 in #firmware-and-baremetal

How to optimize handling of multiple inputs efficiently on STM32F4 using GCC?

Good day everyone, I am using an STM32F4 series (F429ZI) microcontroller clocked at 180 MHz, and I'm compiling my code using GCC for ARM. I have a series of 40 if statements that each check an input for an embedded board. Running through these statements is very slow.

uint32_t INPUT_ARRAY[40];
#define INPUT_X INPUT_ARRAY[0] // input 1 corresponds to the first array slot and so on, easy to call up a specific input.

void main(){
    while(1) // infinite loop for embedded program
    { 
        Read_Inputs(); // input read function

        Write_Outputs(); // output write function

        Logic_Test(); // This is to test out the inputs and outputs on our hardware test rig
    }
}

inline void Logic_Test(void){
    if ( INPUT_1 != 0){
       output_3 |= some_bit // this logic could change
       output_10 |= another_bit 
    }
    if ( INPUT_2 != 0){
       output_x |= some_bit 
    }
    if ( INPUT_3 != 0){
       output_x |= some_bit 
    }
    if ( INPUT_4 != 0){
       output_x |= some_bit // this logic could change
    }
    if ( INPUT_X != 0){
       output_x |= some_bit // this logic could change
    }
    // ... repeated for all 40 inputs
    if ( INPUT_40 != 0){
       output_x |= some_bit 
    }
}

uint32_t INPUT_ARRAY[40];
#define INPUT_X INPUT_ARRAY[0] // input 1 corresponds to the first array slot and so on, easy to call up a specific input.

void main(){
    while(1) // infinite loop for embedded program
    { 
        Read_Inputs(); // input read function

        Write_Outputs(); // output write function

        Logic_Test(); // This is to test out the inputs and outputs on our hardware test rig
    }
}

inline void Logic_Test(void){
    if ( INPUT_1 != 0){
       output_3 |= some_bit // this logic could change
       output_10 |= another_bit 
    }
    if ( INPUT_2 != 0){
       output_x |= some_bit 
    }
    if ( INPUT_3 != 0){
       output_x |= some_bit 
    }
    if ( INPUT_4 != 0){
       output_x |= some_bit // this logic could change
    }
    if ( INPUT_X != 0){
       output_x |= some_bit // this logic could change
    }
    // ... repeated for all 40 inputs
    if ( INPUT_40 != 0){
       output_x |= some_bit 
    }
}

The code is structured like this for inputs 1 to 40. They are not if-else-if statements. I would use a switch, but as far as I know, a switch only handles one case at a time, and multiple inputs could be on simultaneously. Is there a more efficient way to handle all the inputs without so many "if" statements?

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