Making the faulty HP-50g alarm function predictable and useful

[Johnny Shek]

(08-31-2024 11:14 AM)SammysHP Wrote:  Instead of empirically finding rules how to set alarm so that it works in some mysterious way, I'd be more interested in actual reverse engineering or technical analysis of the alarm handling. Is there a layer that uses the watchdog and an interrupt to wake up? Is it implemented directly in the ROM?

Thank you very much for your reply.

This has been a long-standing issue since probably the earliest ROM version of the HP-49g+. Some users posted the issue to user groups or forums, which caught the attention of some HP’s ‘internal guys’. They told Kinpo to fix it. According to the conversations and my understanding, this issue is related to a synchronisation problem between the Saturn emulation layer and the ARM CPU. It has nothing to do with the Saturn code and so the HP-49g has no such issue. Unfortunately, this issue still exists in the latest ROM version of the HP-50g. It seems that the fix would not be simple.

https://groups.google.com/g/comp.sys.hp48/c/Pn7xRbcM5Ow

I had not used the alarm feature since the era of the HP-48SX until recently. In June, I started to look into the issue and designed a lot of programs as well as tests to identify certain patterns to enable me to find a workaround. Hopefully, some users find my information helpful if they still want to use the alarm feature under ROM version 2.15.