Posted on May 17, 2011 at 13:43It's worse than you think. Hardware values (like RTC) can change without interrupts happening.
Suppose the RTC happens to be 0x2345 (high) and 0xFFFF (low)
And you read the low value = 0xFFFF
Then the RTC counts once to 0x2346 (high) and 0x0000 (low)
Then you read the high value as 0x2346.
Your return value is 0x2346FFFF - much higher than real-time.
I do code like:
uint16_t h1, l, h2;
h2 = RTC_CNTH;
do { /* code to catch overflow from low short to high short */
h1 = h2;
l = RTC_CNTL;
h2 = RTC_CNTH;
} while (h1 != h2);
return l | (h1 << 16);
Hope this helps,
Danish
