Error in CMOS Time and Date code?

[bwat]

Can someone take a look at this page:

http://wiki.osdev.org/CMOS

go down to the C code example with the heading "Reading All RTC Time and Date Registers". Now look at the do-while loop which contains the comment "This uses the "read registers until you get the same values twice in a row". Is the condition in the do-while loop not wrong? instead of

Code: Select all

    } while( (last_second == second) && (last_minute == minute) && (last_hour == hour) &&
               (last_day == day) && (last_month == month) && (last_year == year) &&
               (last_century == century) );

would you not want its negation:

Code: Select all

    } while( ! (last_second == second) && (last_minute == minute) && (last_hour == hour) &&
               (last_day == day) && (last_month == month) && (last_year == year) &&
               (last_century == century) );

[sortie]

Hi bwat - you do realize you didn't actually negate the full expression - just one of its terms?

[bwat]

Well spotted! The idea was to negate the entire conjunction not just the first conjunct.

[Nessphoro]

It looks correct to me:
Fetch new values while they're the same... that is exactly what the coder wanted.

[bwat]

But the comment in the code is "This uses the "read registers until you get the same values twice in a row" - emphasis mine. Surely reading the same values twice means it has stabilised.

[Brendan]

Hi,

Can someone take a look at this page:

http://wiki.osdev.org/CMOS

go down to the C code example with the heading "Reading All RTC Time and Date Registers". Now look at the do-while loop which contains the comment "This uses the "read registers until you get the same values twice in a row". Is the condition in the do-while loop not wrong?

It was wrong - I've changed it.


Cheers,

Brendan

[bwat]

A big thank you to you and everyone who contributes to the wiki. Your efforts are appreciated!