32-bit acorn hardware • Puzzling over RTC year logic with PCF8583? RISC OS behavior?

TLDR, is there any known issues with RISC OS machines and the year maintained by the clock (assuming good battery) if the machine has been off for more than 5 years?

Reason for the ask is as follows. I understand that the PCF8583 chip is used in the 32-bit hardware acorn computers for RTC, and as it happens in Dave Hitchens AP6 expansion for the Electron Plus 1.

I am finishing up some 6502 code to support reading/writing date/time to enable this for AP6 users. The chip is great in that it has some free storage for settings. But frustrating that it only has 4 year clock After researching this I found this logic, https://github.com/xoseperez/pcf8583/bl ... 3.cpp#L125, specifically the getYear routine using some of the additional storage and logic to compensate for this situation.

From what I can understand from the getYear code there appears to be a passage of time limitation with the approach (assuming I am understanding the code correctly that is). So.... I wanted to check with folks here to see if they have seen or know of odd effects regarding the year with RISC OS computers using this chip. Because if not, I am wondering what RISC OS code does in this regard?

So here is what (i think) is going on...

• When the year is set an offset is calculated and stored in the user storage, later used to calculate full year

• The last year set value is also stored in the user storage, this is used to check if offset needs to be updated

• The checking is only done on read for the RTC, aka execution of this logic

• From what I can see this depends on the computer being switch on at least before 5 years have passed

• If the computer is switched on within 5 years the code compares current year with last stored

• If the last stored year is greater than the current device year (4 year one) the offset gets 4 years added to it

• If the computer is not switched on within 5 years, the offset will still get updated but will fall short

Am I missing something?

Statistics: Posted by !FOZ! — Mon Jul 01, 2024 4:55 am

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