Problem with reading from PROGMEM array

Projects Programming
1

Hello,

I'm currently writing a program that reads an array of times and frequencies to play a song using a buzzer. However, I'm having some trouble reading data from the array, which is stored in PROGMEM. Here is the code:

const uint16_t m1durs[] PROGMEM = {
0,0,0,0,0,0,0,227,240,467,480,707,720,947,.......,95280,95399,95520,96887,
}


m1size = sizeof(melody1) / sizeof(pgm_read_word_near(&melody1[0]));
Serial.println(m1size);
 
placeholderduration = pgm_read_word_near(&m1durs[m1size-1]);
Serial.println(placeholderduration);

As you can see, I'm trying to read the last value in the array. However, while m1size prints out correctly (~940 numbers), placeholderduration prints out a value of around 31000--far from the actual value that should be read.

This weird behavior didn't occur with a different array I had used earlier, though, so I'm really at a loss. Is there something I'm doing wrong?

2

Did you use "#include <avr/pgmspace.h>" earlier in the code?

Also, which IDE are you using? Shortly above IDE 1.5 (I think it is 1.5.6 and up), the PROGMEM usage changes.

3

The last values are too large for uint16_t (max 65535). You need uint32_t.

m1size = sizeof(melody1) / sizeof(pgm_read_word_near(&melody1[0]));

What is that pgm_read_word_near doing there? Completely useless, throw it away!

4

oqibidipo:
The last values are too large for uint16_t (max 65535). You need uint32_t.

m1size = sizeof(melody1) / sizeof(pgm_read_word_near(&melody1[0]));

What is that pgm_read_word_near doing there? Completely useless, throw it away!

Oh, that makes a lot of sense. I can't believe I missed that >.<

So you're saying I can just do

m1size = sizeof(melody1) / sizeof(melody1[0]);

or... something else?

5

P0ke:
So you're saying I can just do

m1size = sizeof(melody1) / sizeof(melody1[0]);

Exactly.