I am thinking to write a sketch where an arduino mega 2560 will pull several output pins low and high depending on the state of several input pins. I want to use port manipulation to do that. The code will probably be like 150 to 200 lines long and for that reason i fear that eventually i will make some mistake like confuse DDR, PORT or some bitwise operation and ruin the sketch.
I have very very poor knowledge of programing in general. That said, here is what i thought:
Maybe i can use the #define in order to avoid mistakes and "simulate" the digitalRead and digitalWrite functions.
I wrote a small test code that will turn off the built in led (on an uno board) if pin 2 goes low.
Arduino IDE does not generate any error and the code seems to work all right but i thought to ask because some times things are ment to be used in different ways. Maybe #define isn’t met to work like that?
Thank you !
//TURN OFF THE BUILT IN LED WHEN ARDUINO PIN 2 GOES LOW
//USING PORT MANIPULATION AND #define
#define PB5HIGH (PORTB = (1 << 5) | PORTB) // Turn built in led on
#define PB5LOW (PORTB = ~ (1 << 5) & PORTB) // Turn built in led off
#define CHECK_BTN_STATE ( (PIND & (1 << 2)) >> 2 )
void setup()
{
DDRB = (1 << 5) | DDRB; // Seting PORTB 5th bit as output.
DDRD = ~ (1 << 2) & DDRD; //Seting PORTD 2nd bit as input. Arduino pin 2.
PORTD = (1 << 2) | PORTD;// Enable pullup on Arduino pin 2.
PORTB = ~ (1 << 5) & PORTD; // Seting PORTB 5th bit low,
}
void loop()
{
if (!CHECK_BTN_STATE)
{
PB5HIGH;
}
else
{
PB5LOW;
}
}
ex:
Here we prove it is 800ns faster to place flag checking at the front of a compound if() statement rather than at the end.
you do know that it is because the the first condition is 'false' and therefore the second condition after the '&&' never gets evaluated (as if the first is 'true' and the logical '||' . Of course just checking a flag is quicker than doing a calculation on the result of a call to millis(), but if the flag is 'false' there is no difference in time (i hope !)
#define PB5HIGH (PORTB = (1 << 5) | PORTB) // Turn built in led on
#define PB5LOW (PORTB = ~ (1 << 5) & PORTB) // Turn built in led off
#define CHECK_BTN_STATE ( (PIND & (1 << 2)) >> 2 )
I think this is a very elegant solution. Note the braces around the whole definition. This assures that any operation within them is done by the compiler.
i thought i explained that if the first condition is false, the second does not get evaluated. (in case of &&), that it is quicker to evaluate a 1 Byte than a 4 Byte calculation which includes the result from a call to a function seems obvious.
I am getting a little bit off topic but i guess it is all right since i have my answer for the initial question.
I mentiond my very poor knowledge on programming not because i am beign modest but because it is a fact.
I first discovered the world of programming including embedded systems about a year ago and since then i try to learn as much as i can any way i can. It is not that i dont have the mental capacity to learn. what i lack is someone to teach/guide me. I can definetly not cafford to pay for classes and i struggle to learn from youtube or any other way possible. I have also tried a couple of books like (Pic microcontroller projects in C by ibrahim dogan) but it is nearly impossible for me to understand... Not to mention that the closest thing to a mentor for me when it comes to programming are you people here.
Anyways Thank you all. You made me a happy man today with your kind words.
