very long PROGMEM array address is wrong

Using Arduino Programming Questions
#1

Here's my problem : I have several arrays of 16383 ints which means that the address of the second array is over an int possibility. When i try to access this array, the address is cast to an int and therefore is wrong.

Here's a snippet of code:

const uint16_t tab0[16383] PROGMEM = {...};
const uint16_t tab1[16383] PROGMEM = {...};

void loop() {
    Serial.println(long(&tab0), HEX); //prints 0xFFFF810a instead of 0x1810a 
}

Is there a way to cast an address as long, or do i have to manually write the correct address by looking at the disassembly code?

Thx for your help.

#2

Here's a snippet of code:

In which the Serial.print() statement has 5 parens... Post some code that ACTUALLY compiles.

#3

Fixed.

#4

chairn:
Fixed.

sketch_jan10a:1: error: expected primary-expression before '...' token
sketch_jan10a:2: error: expected primary-expression before '...' token

NOT fixed.

#5

What board are you using?

#6

Cast to an unsigned long.  Serial.println((unsigned long)(&tab0), HEX);

#7

aarg:
Cast to an unsigned long.

  Serial.println((unsigned long)(&tab0), HEX);

Doesn't work, same result.

robtillaart:
What board are you using?

ATmega 2560

PaulS:
NOT fixed.

... When the anti-spam protection will allow me to edit.

Anyway, i think it's not possible because pointers are treated as int, i.e 16 bits int, which does not allow addressing more than 32KB.

#8

Then you have to post all your code.

#9

Hello and welcome,

Try

Serial.println( pgm_get_far_address( tab0 ), HEX );
#10

PROGMEM above 64k example:

const char above[1024] PROGMEM = "above 64";
const char filler1[31 * 1024] PROGMEM = "filler1";
const char filler2[31 * 1024] PROGMEM = "filler2";
const char below[4 * 1028] PROGMEM = "below 64";

void setup() {
  Serial.begin(115200);
  dumpFF(pgm_get_far_address(below), 0x20);
  dumpFF(pgm_get_far_address(filler1), 0x20);
  dumpFF(pgm_get_far_address(filler2), 0x20);
  dumpFF(pgm_get_far_address(above), 0x20);
}

void dumpFF(unsigned long adr, int len) {
  byte idx;
  if (len) {
    for (; len > 0; len -= 16, adr += 16) {
      phBytesB((byte*)&adr, 4);
      Serial.write(':');
      Serial.write(' ');
      for (idx = 0; idx < 16; idx++) {
        if (idx < len ) {
          phByte(pgm_read_byte_far(adr + idx));
          Serial.write(' ');
        } else {
          Serial.print(F("   "));
        }
      }
      Serial.write('\'');
      for (idx = 0; (idx < 16) && (idx < len); idx++) {
        byte curr = pgm_read_byte_far(adr + idx);
        Serial.write(curr < 0x20 ? '.' : curr);
      }
      Serial.write('\'');
      Serial.println();
    }
  }
}

void psdec(void (*pprint)(byte), byte* ptr, byte len) {
  for (ptr += len - 1; len--;) {
    (*pprint)(*ptr--);
  }
}

void phBytesB(byte* ptr, byte len) {
  psdec(phByte, ptr, len);
}

void phByte(byte val) {
  phNibble(val >> 4);
  phNibble(val);
}

void phNibble(byte val) {
  val &= 0xF;
  Serial.write(val + (val < 10 ? '0' : 'A' - 10));
}

void loop() {}
#11

Here is how i’ve done it + using pgm_read_word_far for reading.

const uint16_t tab0[16383] PROGMEM = {0};
const uint16_t tab1[16383] PROGMEM = {0};
const uint16_t tab2[16383] PROGMEM = {0};
const uint16_t tab3[16383] PROGMEM = {0};
const uint16_t tab4[16383] PROGMEM = {0};
const long tab[] = {(long)&tab0, (long)&tab1, (long)&tab2, (long)&tab3, (long)&tab4};

void setup() {
  // put your setup code here, to run once:
    Serial.begin(115200);
    Serial.println(tab[0], HEX); //104
    Serial.println(tab[1], HEX); //FFFF8106
    Serial.println(tab[2], HEX); //108
    Serial.println(tab[3], HEX); //FFFF810A
    Serial.println(tab[4], HEX); //10C

    Serial.println(pgm_read_word_far(&tab0 + 12); //example
}

And the real addresses are (looking at the assembly code) :
0000010c <__trampolines_end>: //tab4
…

0000810a <_ZL4tab3>:
…

00010108 <_ZL4tab2>:
…

00018106 <_ZL4tab1>:
…

00020104 <_ZL4tab0>:
…

edit: with pgm_get_far_address, i have the following results:
20104
18106
10108
810A
10C

So, i guess my problem is solved. I just dont get why this function is not there :
http://www.nongnu.org/avr-libc/user-manual/group__avr__pgmspace.html

#12