Hi all,
I am fairly new to the world of uC programming. I've been using avr-gcc
4.3.2 with ATmega168 and stumbled upon something rather peculiar.
Please consider the following code snippet (the crux of the matter is in
the last block of code):
#include "lcd.c"
// Day-of-week names
char dow0[] PROGMEM = "Ned";
char dow1[] PROGMEM = "Pon";
char dow2[] PROGMEM = "Uto";
char dow3[] PROGMEM = "Str";
char dow4[] PROGMEM = "Stv";
char dow5[] PROGMEM = "Pia";
char dow6[] PROGMEM = "Sob";
// Days of week in an array.
PGM_P dow[] PROGMEM = { dow0, dow1, dow2, dow3, dow4, dow5, dow6 };
// Time struct from BQ3285
typedef struct {
// time values
uint8_t sec; // seconds (0..59)
uint8_t min; // minutes (0..59)
uint8_t hour; // hours (0..11, or 0..23 if BQ_HF is set in BQ_REG_B)
// calendar values
uint8_t dow; // day of week (1..7, 1 = Sunday)
uint8_t day; // day of month (1..31)
uint8_t month; // month (1..12)
uint8_t year; // year (0..99)
} bq_time_t;
// current time
volatile bq_time_t now;
// ...
/* called from interrupt handler */
// write the day of week
uint8_t k = 1;
uint8_t l = now.dow;
lcd_write_int16(k); lcd_putc(','); // outputs: 1
lcd_write_int16(l); lcd_putc(','); // outputs: 1 (now.dow is inited to
1 outside)
lcd_write_int16(k==l); lcd_putc(','); // outputs: 1 (as it should)
lcd_write_int16(dow[k]); lcd_putc(','); // outputs: address in dow[1] in
pgm. space
lcd_write_int16(dow[l]); lcd_putc(','); // outputs: 0 (?!)
Whenever I try to index the dow[] array using a value from now.dow, I
get zero. This is all the more interesting, because the following
block, albeit unreasonable, works just as advertised:
switch (now.dow-1) {
case 0: lcd_write_string_P(dow[0]); break;
case 1: lcd_write_string_P(dow[1]); break;
case 2: lcd_write_string_P(dow[2]); break;
case 3: lcd_write_string_P(dow[3]); break;
case 4: lcd_write_string_P(dow[4]); break;
case 5: lcd_write_string_P(dow[5]); break;
case 6: lcd_write_string_P(dow[6]); break;
default: lcd_write_string_P(PSTR("???")); break;
}
// But this doesn't: lcd_write_string_P(dow[now.dow-1]);
Any help would be more than appreciated.
Thanks,
Zoran
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