Using the F() macro to save text for LCD in flash

Using Arduino Programming Questions
#1

I've run into a problem with a library I'm using, I'm guessing it's just a little detail to fix, but I'm at a loss.
Normally, with most LCDs and libraries, I would do something like this:
LCD.println(F("HELLO WORL"));

I have this lcd/keyboard controller that comes with a library the manufacturer wrote. It all works well (so far) except I can't save text to the flash memory via F(). An example would be:

disp.lcd_cls(); // clear display
disp.lcd_rowcol(0, 2); //row, col
disp.lcd_print("DRILL TABLE MENU");

in this example, I need to do this, but it won't work:

disp.lcd_print(F("DRILL TABLE MENU"));

It is THIS LCD/KEYPAD CONTROLLER as seen here:

I'm using I2C, and THE LIBRARY IS HERE, which he wrote. I talked to him about it, and he wasn't familiar with the Flash () function.
Is it hard to implement this into his library? I have a lot of text to display and will have to have the F() function.
Thanks,

#2

Is it hard to implement this into his library?

No… although I haven’t looked at the code, because I won’t download from external sites. If you attach it to your post, I would take a look. There are probably two easy ways:

1) Derived his class from the Print class. You must make sure the single-character write method is overridden in his class:

        virtual size_t write(uint8_t c);

The Print class will use that method to provide all the other print methods (int, float, char *, etc.).

2) Add a method to his class, using Print.cpp as an example:

size_t LCDclassName::print(const __FlashStringHelper *ifsh)
{
  PGM_P p = reinterpret_cast<PGM_P>(ifsh);
  size_t n = 0;
  while (1) {
    unsigned char c = pgm_read_byte(p++);
    if (c == 0) break;
    if (write(c)) n++;
    else break;
  }
  return n;
}

The F macro result is of type const __FlashStringHelper *, so that’s the method you need to provide.

The first technique is best, as you may be able to eliminate a bunch of code from his library, duplicating what the Print class is already providing. The second technique may quicker for you if you aren’t familiar with C++ classes.

Cheers,
/dev

P.S. The Print class source code, Print.h and Print.cpp, is in the Arduino install directory, under hardware/arduino/avr/cores/arduino.

#3

Thanks for looking into this. It’s all greek to me. (I’m a self talk arduino-er).
These are the 2 files in the library, plus the examples.

bv4619_I.cpp (7.36 KB)

bv4619_I.h (1.62 KB)

#4

I looked at both those files, .cpp and .h, but I can't make sense of what was recommended to fix the problem. Can someone point me in the right direction? I'd sure appreciate it.

#5

You’ll have to do option 2. Add this to the H file, at line 39:

        void lcd_print(const __FlashStringHelper *ifsh);

Add this to the CPP file, at line 131:

void LCD::lcd_print(const __FlashStringHelper *ifsh)
{
  Wire.beginTransmission(_i2adr);
  Wire.write(3); // data

  PGM_P p = reinterpret_cast<PGM_P>(ifsh);
  while (1) {
    char c = (char) pgm_read_byte(p++);
    if (c == 0) break;
    Wire.write(c);
  }

  Wire.write(13); // always finish with 13  
  Wire.endTransmission();
  delay(1);
}

Then add this to the CPP file, at line 27:

#include <avr/pgmspace.h>

Cheers,
/dev

#6

Thanks so much! I'll check this out tomorrow. I normally like to fully understand everything I get help with on the forum, but I this library stuff is SO over my head, I know I won't. Thanks from me, and I'll forward to update to the library developer.
Cheers,

#7

/dev:
You’ll have to do option 2. Add this to the H file, at line 39:

        void lcd_print(const __FlashStringHelper *ifsh);

Add this to the CPP file, at line 131:

void LCD::lcd_print(const __FlashStringHelper *ifsh)

{
  Wire.beginTransmission(_i2adr);
  Wire.write(3); // data

PGM_P p = reinterpret_cast<PGM_P>(ifsh);
  while (1) {
    char c = (char) pgm_read_byte(p++);
    if (c == 0) break;
    Wire.write(c);
  }

Wire.write(13); // always finish with 13 
  Wire.endTransmission();
  delay(1);
}



Then add this to the CPP file, at line 27:

#include <avr/pgmspace.h>



Cheers,
/dev

Actually, this is one of those times that you can use assignment in a conditional clause.

void LCD::lcd_print(const __FlashStringHelper *ifsh)
{
  Wire.beginTransmission(_i2adr);
  Wire.write(3); // data

  PGM_P p = reinterpret_cast<PGM_P>(ifsh);
  char c;
  while( c = pgm_read_byte(p++) )
  {
    Wire.write(c);
  }

  Wire.write(13); // always finish with 13  
  Wire.endTransmission();
  delay(1);
}
#8

Actually...

LOL, there's lots of things I would rewrite from the Arduino core. That snippet is from Print.cpp. Or just use Cosa. :wink:

#9

if you left the AVR behind and used some other processor, all the proprietary progmem kludes in AVR libC to get around the AVR h/w architecture incompatibilities with C would vanish.
i.e. with other micro-controllers const just works as was intended and required by C.

--- bill

#10