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allenhuffman
Joined: 17 Jun 2019
Posts: 552
Location: Des Moines, Iowa, USA
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| Exploring PIC24 rtc_read()/rtc_write() |
 Posted: Tue Nov 05, 2024 11:17 am |
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Just something for future searches to find. I am experimenting with 24FJ256GA106 real time clock hardware.
Can someone clarify my understanding is correct? The help file is quite vague on rtc_read()/rtc_write() and the parameters of the rtc_time_t structure should be set to.
| Code: | typedef struct {
unsigned int8 tm_year;
unsigned int8 tm_temp; // Not used by built in functions, place holder only do not use
unsigned int8 tm_mday;
unsigned int8 tm_mon;
unsigned int8 tm_hour;
unsigned int8 tm_wday;
unsigned int8 tm_sec;
unsigned int8 tm_min;
unsigned int8 tm_isdst; // Not used by built in functions
} rtc_time_t; |
Based on looking at code examples, it looks like tm_year is Base-2000, so setting it to 0 means 2000, and 24 would mean 2024.
Other values seem to be base-1, so 1-12 for the tm_mon, 1-31 for the tm_mday, and the same four hour, min and sec.
Is this understanding correct? The reason I ask is I see things in the sample time.h/time.c files that do things to convert the RTC numbers back to C-time.
rtcperepheral.c does:
| Code: | void GetTime(struct_tm *pRetTm)
{
struct_tm cTime;
rtc_time_t datetime;
rtc_read(&datetime);
// adjust date to be time.h compatible
cTime.tm_year = datetime.tm_year + 100; // starting at 1900
cTime.tm_mon = datetime.tm_mon - 1; // 0-11
cTime.tm_mday = datetime.tm_mday - 1; // 0-30
cTime.tm_wday = datetime.tm_wday - 1; // 0-6
cTime.tm_hour = datetime.tm_hour;
cTime.tm_sec = datetime.tm_sec;
cTime.tm_min = datetime.tm_min;
memcpy(pRetTm, &cTime, sizeof(struct_tm));
} |
This confuses me, since it implies the clock is base 1900, and adds 100 to the year.
Likewise, it shows mon, mdw and wday as being base-1, so it subtracts. But in the C standard it looks different:
https://cplusplus.com/reference/ctime/tm/
struct tm shows base-1 for tm_mday -- 1-31. The others it shows as base-0 (seconds, minutes, hours, months since January, days since Sunday, etc.)
If the intent of this code was to provide a struct_tm compatible structure, maybe that is just an error in the code. I believe if I used these time routines, it would be providing different results than cTime (even the code uses cTime for a variable name, which makes me think it is supposed to look like the C time structure).
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ? |
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jeremiah
Joined: 20 Jul 2010
Posts: 1348
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| Posted: Tue Nov 05, 2024 11:47 am |
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The C standard doesn't have an rtc_time_t type, so I wouldn't compare them. In general, it would really come down to how the PIC implements the RTC registers as to what the time base is, so I would refer to the datasheet for your PIC to see what the RTC does for year month day, etc. As for the year, I don't recall if it is 1900 or 2000, but I would have guessed 1900 since most RTCs are 2 digit year and the PIC has been around since the 1900s, but it was only a guess.
I would do similar to what you are doing and just test it out and see what it gives and adjust my code accordingly. |
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allenhuffman
Joined: 17 Jun 2019
Posts: 552
Location: Des Moines, Iowa, USA
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| Posted: Tue Nov 05, 2024 12:38 pm |
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Testing seems to verify the sample code incorrect unless the clock hardware is base-2 for some reason. The CCS code addresses using it with standard C (even providing an offset you apply to time_t to go between the "seconds since 1/1/2010" mode and standard C). Using that...
| Quote: | 31536000 seconds in a year.
86400 seconds in a day
31622400 seconds in a leap year.
1729810550 seconds since 1/1/1970
STD: 2024-11-05 18:21:55 is 1730830915 seconds since 1/1/1970
STD: 2024-11-05 18:21:55 is 468526915 seconds since 1/1/2010
CCS: 2024-11-05 18:21:55 is 1730830915 seconds since 1/1/1970
CCS: 2024-11-05 18:21:55 is 468526915 seconds since 1/1/2010 |
My test code:
https://onlinegdb.com/iTMTsbydwT
The datasheet for my PIC specifically mentions year values of 2000 to 2099, so that looks like 0 for 2000.
For month (MTH), it shows you can pass in 0-1 for the tens digit, and 0-9 for the ones. That would give 0-19 for the month, looking like it is base 0.
The same for day (DAY) using 0-3/0-9, allowing 0-39.
I do not see where it specifically says base 0 or base 1, so I "assume" it is base 0. But, since it shows values higher than we could use, maybe it also shows a 0 value that is lower than we can use and is really base 1.
I'll have to test that. ChatGPT tells me it is base-1, but ... yeah, never trust the 'bot ;-)
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ? |
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allenhuffman
Joined: 17 Jun 2019
Posts: 552
Location: Des Moines, Iowa, USA
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| Posted: Tue Nov 05, 2024 12:51 pm |
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It is looking like Base-0 for the PIC24's RTC. I set the month to 0, and I see it rolls over to 1 after day 30:
| Quote: | 2000-00-30 23:59:59
2000-01-01 00:00:00
2000-01-01 00:00:01
2000-01-01 00:00:02
2000-01-01 00:00:03
2000-01-01 00:00:04
2000-01-01 00:00:05
2000-01-01 00:00:06
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_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ? |
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allenhuffman
Joined: 17 Jun 2019
Posts: 552
Location: Des Moines, Iowa, USA
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| Posted: Tue Nov 05, 2024 12:58 pm |
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I stand corrected.
| Quote: | 2000-01-31 23:59:57
2000-01-31 23:59:58
2000-01-31 23:59:59
2000-02-02 00:00:00
2000-02-02 00:00:01
2000-02-02 00:00:02
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The RTC hardware seems to like base-1 for the day. This matches the C time.h struct tm where day of month is 1-31, but others are 0. A few more tests needed...
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ? |
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allenhuffman
Joined: 17 Jun 2019
Posts: 552
Location: Des Moines, Iowa, USA
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| Posted: Tue Nov 05, 2024 1:07 pm |
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Base-1 it is.
| Quote: | 2000-12-31 23:59:55
2000-12-31 23:59:56
2000-12-31 23:59:57
2000-12-31 23:59:58
2000-12-31 23:59:59
2001-01-01 00:00:00
2001-01-01 00:00:01
2001-01-01 00:00:02
2001-01-01 00:00:03
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Not sure if I need to do anything with tm_wday but for future reference, my test code:
| Code: | // Setup the real time clock.
setup_rtc (RTC_ENABLE | RTC_OUTPUT_SECONDS, ZERO);
// Set time to default if on a fresh power cycle.
rtc_time_t datetime;
if (RestartCause == RESTART_POWER_UP)
{
DEBUG_PRINTF ("Set ");
// Initialize time to 1/1/2000 00:00:00.
datetime.tm_year = 0; // Base-2000
datetime.tm_mon = 12; // December(base 1)
datetime.tm_mday = 31; // 31st (base 1)
datetime.tm_hour = 23; // hh
datetime.tm_min = 59; // ss
datetime.tm_sec = 50; // mm
datetime.tm_wday = 0;
datetime.tm_temp = 0; // Not used.
datetime.tm_isdst = 0; // Not used.
rtc_write (&datetime);
}
// Get current date and time.
rtc_read (&datetime);
DEBUG_PRINTF ("%04u-%02u-%02u %02u:%02u:%02u) ",
datetime.tm_year + 2000, datetime.tm_mon, datetime.tm_mday,
datetime.tm_hour, datetime.tm_min, datetime.tm_sec);
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_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) http://www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC24 programmer.
http://www.whywouldyouwanttodothat.com ? |
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