PROGMEM not working with uint32_t?

Projects Programming
1

I'm attempting to use PROGMEM to store an array of uint32_t, and I'm having problems. I can make PROGMEM work with uint16_t, so I suspect (1) I'm doing something wrong, (2) I've found a bug, or (3) the compiler is messing things up.

I'm running arduino.cc 1.8.5.

Here's the code:

const uint32_t PROGMEM array32[] = { 0x00FFEEDD, 0x00CCBBAA, 0x00998877, 0x00665544, 0x00332211, 0x00000000 };
const uint16_t PROGMEM array16[] = { 0x1122, 0x3344, 0x5566, 0x7788, 0x99AA, 0xBBCC };

uint32_t stepStart;
uint16_t index;

void setup() {
  // put your setup code here, to run once:
  stepStart = millis();
  Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
  int step = 3000;
  int color;
  uint32_t mark = millis();
  // print another array value every 3 seconds to avoid overwhelming anyone reading the serial
  if (mark > (stepStart + step)) {
    // output next color
    Serial.print("color ");Serial.print(index,DEC);Serial.print(" at ");
    // if I change uint32_t to uint16_ and array32 to array16 in the next 3 lines, the code works.
    Serial.print((uint32_t) (array32+index));Serial.print(" is ");
    color=(uint32_t) pgm_read_dword_near(array32+index);
    Serial.println( (uint32_t) color,HEX);
    index++;
    index %= 6;
    stepStart = mark;
  }
}

Serial output:

color 0 at 104 is FFFFEEDD
color 1 at 108 is FFFFBBAA
color 2 at 112 is FFFF8877
color 3 at 116 is 5544
color 4 at 120 is 2211
color 5 at 124 is 0

I've taken a look at the compiler output with a binary editor, and (1) I can see the compiler's smart enough to load only the array I'm using (array32 in this case), (2) it doesn't appear to load the array32 correctly. Here's a portion of the hex file:

0x0120 0DDEEFF00AABBCC0
0x0130 083.:10007000778
0x0140 8990044556600112
0x0150 233000000000083.

Any ideas? Did I miss something basic, or did I potentially find a bug?

2

gnealhou:

    color=(uint32_t) pgm_read_word_near(array32+index);

http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html#gaf51eeaa847dd2668d2a66b70ecfb7398

...versus...

http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html#ga7fa92c0a662403a643859e0f33b0a182

3

Good eye, but it works the same with pgm_read_dword_near vs. pgm_read_word_near. I just missed it on my last conversion from using array16 to array32.

I edited my original post to reflect the correct use of pgm_read_dword_near, and I have tested it with both macros.

4

The problem is:

int color;

which should be uint32_t color;

also... I don't think you initialise index

should be

uint16_t index= 0;

Yours,
TonyWilk

5

TonyWilk:
The problem is:

int color;

which should be uint32_t color;

:slight_smile: Good catch !

6

TonyWilk:
The problem is:

int color;

which should be uint32_t color;

This was the problem (and I got lucky on the non-initialized index). Thanks, Tony!

7

gnealhou:
This was the problem (and I got lucky on the non-initialized index). Thanks, Tony!

Both index and stepStart were initialised to zero by crt0