reducing the amount of code in ram to free up space

Projects Programming
19

Here are pieces of code I used to put menu into PROGMEM. I also put error messages, etc, there.

You need some #includes to use PROGMEM:

#include <avr/io.h>
#include <avr/pgmspace.h>

Here I have a 7 line menu (80 characters per line) stored to PROGMEM, and a special pointer to get the data with:

const char PROGMEM usageMsg[][80] = { // all this text stored in flash
  "          Piezo touch sensor tuner.",
  "Adjust vertical; enter W to subtract or X to add, and a number 0-255",
  "Adjust timescaler; enter A to subtract or D to add, and 0-16535",
  "to add 250 to vertical enter W250 in Serial Monitor and press enter",
  "seperate multiple commands with spaces; ex: W25 D240",
  "    ** this message stored in flash ram **",
  "    ** and printed with a 1 byte buffer ** :-P"
};

PGM_P Msg; // pointer into flash memory

The full program stores -every- const char string (not C++ String!) in PROGMEM. It has serial user I/O error messages, etc, as well as the menu.

I made this function to print the stored strings one char at a time:

void  printMsg( PGM_P FM )
{
  do 
  {
    B = pgm_read_byte( FM++ );    // FM++ is pointer math; look Ma, no indexes!
    if ( B )  Serial.print( B );
  }
  while ( B ); // when it reaches the terminating zero, it exits
}

And this function just to print the whole menu:

void printHelp(void)
{
  for ( byte i = 0; i < HELPLINES; i++ )
  {
    printMsg( usageMsg[ i ]);
    Serial.println();
  }
  Serial.println();
}