PROGMEM issues with Arduino 1.6.x and how to fix them

WP_20140826_22_20_46_ProThere is a new version of the Arduino IDE out, version 1.6.1. If you do not have, you can go to the Arduino web site and grab yourself a copy.  It is much faster than the older versions.  Overall, it seems to be better in most aspects. Except for one…the new compiler breaks some of your code.

I installed it and then tried to compile Half-Byte Tiny Basic.  Expecting a clean compile, I was surprised by the errors it generated.  Upon investigation, I found that the references to PROGMEM was the cuprit. Further research revealed a fairly easy remedy, but one that was difficult to find, so I thought I’d make it easier.

Error:  variable ‘message’ must be const in order to be put into read-only section by means of ‘__attribute__((progmem))

So, this was the first error, which led to a second error that isn’t really an error (it goes away when you fix this) so I’m not going to talk about it, it is one that is safe to ignore.  Now, simply changing ‘Static’ to ‘Const’ does not actually fix the problem. No, like the error says, you need to specify the SECTION to put it in.  Look at the old way below, then check out the new way.

OLD WAY:
/***********************************************************/
// Keyword table and constants – the last character has 0x80 added to it
static unsigned char keywords[] PROGMEM = {
‘L’,’I’,’S’,’T’+0x80,
‘L’,’O’,’A’,’D’+0x80,
‘N’,’E’,’W’+0x80,
‘R’,’U’,’N’+0x80,
‘S’,’A’,’V’,’E’+0x80,
….
‘S’,’C’,’R’,’O’,’L’,’L’+0x80,
0
};
NEW WAY:
/***********************************************************/
// Keyword table and constants – the last character has 0x80 added to it
static unsigned char __attribute((section(“.progmem.data“))) keywords[] = {
‘L’, ‘I’, ‘S’, ‘T’ + 0x80,
‘L’, ‘O’, ‘A’, ‘D’ + 0x80,
‘N’, ‘E’, ‘W’ + 0x80,
‘R’, ‘U’, ‘N’ + 0x80,
‘S’, ‘A’, ‘V’, ‘E’ + 0x80,

‘S’,’C’,’R’,’O’,’L’,’L’+0x80,
0
};

Fixing this killed the second error that was showing up.  BUT…

ANOTHER error (third overall) reared its head:

Error: <variable> causes a section type conflict with <section>

Specifying the attribute did the trick, simply using PROGMEM causes issues. While the original error went away (along with that secondary error), the section type error appeared.  This one, though, was simple. I was stuffing two TYPES into the same section and that is a no-no in the new world.  Just adding the code below AND specifying a different section of PROGMEM did the trick. This way allows you to segment your data as well.

// Workaround for http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34734
‪#‎ifdef‬ PROGMEM
‪#‎undef‬ PROGMEM
‪#‎define‬ PROGMEM __attribute__((section(“.progmem.vars”)))
‪#‎endif‬

Once I made these changes, my code compiled and uploaded just fine.  I hope this saves you some time.

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