Alternative HP-41CL mainframe (OS ROMs) update for beta test
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10-08-2019, 06:08 AM
Post: #28
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RE: Alternative HP-41CL mainframe (OS ROMs) update for beta test
Turns out that it was not so easy to sense the Halfnut and fix the lower case characters.
The code itself is some 30 words, but there is no room for it other than in bank 5.2, and that will not work. It is a bit hard to explain, but I ran into this before. The problem is that a pushed return address is just an address, there are no bank bits being pushed. If the called routine fiddles with the bank bits (to call the 30-word slice in bank 2), it loses track of which bank it was originally called from. The result is that it may return to the wrong bank. There are four alternatives as I see it. 1. Restructure code to make room somewhere else for it (in practise it means page 3). 2. Make two different builds, one with and one without the fix the MASK for lower case characters. 3. Assume there is a halfnut display, even though only franken-nut and emulators can make use of it, no ordinary 41CL can. 4. Forget it, at least for now. I do not want to do (3) at least. I rather keep the star-burst character behavior we are used to when not using Halfnuts. |
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