Memory

I've played with Arduinos for a while. The IDE is functional. The API has a really heavy abstraction. That really becomes problematic when you want to start using the ATTINY processors. Lets look at the popular AVRs

	Flash	Ram	EEPROM
tiny 2313	2K	128B	128B
tiny 84	4K	512B	512B
tiny 85	8K	512B	512B
mega 328	32KB	2k	1k

The mega 328 has enough ram to use it carelessly. It's flash size is huge. translating a basic Arduino program into a tiny2313 might be a little challenging. So lets go over a few memory tricks worth mentioning. today we're still going to be using an Arduino as a target since I have one here and most people will too.

Data types int and char are very different beasts. Char is an integer type guaranteed to be 8 bits in size, int is 16bits. so a char is 1 byte, where as an int is 2 bytes. In general, use char when you can. unsigned it'll hold numbers 127 to -126, unsigned will get you 0-255. a trick that helps at least me is declaring the following at the top of my program: unless you need to go larger, chars will make that 128 bytes last a little longer.

Macros are the next bit of memory stretching arduino doesn't teach. if you have unchanging data, or constants, a define is better than a variable. take the following:

#define NUM_PINS 4
int num_pins 4;

The first line will insert a 4 anywhere the compiler sees NUM_PINS. This allows for centralized information without using ram to do it. The second line uses 16 bits to sore 3 bits of data. a char, or unsigned char is better fit, since it only uses 8 bits.

These are basic C items that you can use in the standard Arduino stuff. To get in the habit.

Lets revamp the fade code from the arduino examples a bit. The original uses 15 bytes of memory. the bare example uses 9, so those 6 bytes are from the 3 variables. This one does it in 12 bytes.

/*
 Fade

 This example shows how to fade an LED on pin 9
 using the analogWrite() function.

 This example code is in the public domain.
 */

#define LED 9;           // the pin that the LED is attached to
unsigned char fadeAmount 10;    // how many points to fade the LED by

unsigned char brightness = 0;    // how bright the LED is we need 0 to 255

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 9 to be an output:
  pinMode(LED, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  // set the brightness of pin 9:
  analogWrite(LED, brightness);

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade:
  if (brightness == 0 || brightness == 255) {
    fadeAmount = -fadeAmount ;
  }

  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}