HP48 Clock error data results

[TomC]

Jonathan:
This '72 hour' update detail is very interesting; does this mean that if the machine is awake more often (than every 72 hours), that its clock will be updated more often and hence more accurate?

TomC

(03-02-2021 10:24 PM)Jonathan Busby Wrote:  

(03-01-2021 10:25 PM)TomC Wrote:  What I suspect is that there is something in the software/interrupt structure of the code that causes the user clock to 'lose time'.

One culprit may be display refresh which halts the CPU every 244 μS . Also, AFAIK, while in the 48 ISR, when interrupts are disabled, hardware keyboard scans are disabled, so, that can't be a source of inaccuracy in the timer2 ISR.

Quote:Perhaps we can then study if the clock error is dependent on how often the machine is used/not used/running programs, battery condition, etc...

Well, when the HP48 is in "deep sleep" ( ie. turned off ) the ROM services timer2 only every 72 hours to update the system time, so, the more the machine is used, the more the timer2 ISR is being serviced with the display turned on.

Regards,

Jonathan