From: "bolet (sent by Nabble.com)" <[EMAIL PROTECTED]>
[...]
The program works OK without optimization. It doesn't work with
optimization (-o1). The code is:
...includes...
const char P_Txt[] PROGMEM = "Just a test..";
volatile PGM_P txt= P_Txt;
int main (void)
{
...Init code ... (reg setup & enable int)
do{} while( (a=pgm_read_byte(txt)) ); // Wait for null char
cli(); //Disable int
for (;;); // Do nothing
return(0);
}
SIGNAL (SIG_USART_DATA)
{
UDR0=pgm_read_byte(txt++); //Send a byte and increment pointer
}
The 'do while' assembler code generated (with -o1) :
+00000041: 91E00100 LDS R30,0x0100
+00000043: 91F00101 LDS R31,0x0101
+00000045: 9184 LPM R24,Z
51: do{} while( (a=pgm_read_byte(txt)) ); // Wait for null char
+00000046: 2388 TST R24
+00000047: F7F1 BRNE PC-0x01 Branch if not equal
52: cli();
//Disable int
As you can see, the LPM instruction is outside the loop, so this is an
infinite loop.
-What's wrong with this code?
Seems to be a strange corner case. I'm not sure the compiler is
misbehaving, but it might be. There should be a simple fix.
You've declared 'txt' to be volatile, which is good, but you don't show the
declaration of 'a'. And I suspect it's not volatile. Since 'a' is not
volatile, subsequent writes to the value may be optimized out. But the LPM
should always happen because txt is volatile.
In any case, changing the declaration of 'a' to something like
unsigned char volatile a;
should do it. Removing 'a' entirely should fix it as well, but I'm assuming
you're using it for other reasons.
-Which is this the correct way to work with flash data?
You don't seem to be handling flash wrong.
Any suggestion would be greatly appreciated.
HTH,
-=Dave
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