[41CL WARP] XEQ+ oddness

[Ángel Martin]

(04-10-2021 09:16 PM)cdmackay Wrote:  thanks Sylvain,

(04-10-2021 08:39 PM)Sylvain Cote Wrote:  I had forgotten it, but yes it was very well explained in the ZEPROM Module - Programmer's Manual, 1988, Pages 5 to 9

the discussion there of the 12K HP modules seems to suggest that it is OK to have both a single-page bank-switched module, along with a single-page non-banked module, in the same port?

Yeah, that's ok. There's no need to leave the other page blank: the port can be fully used as long as there aren't two, single-page, bank-switched ROMS in it.

So the rule of thumb is that the only restriction is for two bank-switched ROMS belonging to different Modules to be in the same port, that's what should be avoided - As you observe, the case of two, single-paged, bank-switched modules is a particular instance of the general rule above.

In truth, even that isn't always going to be a problem, only when one of the ROMS is accessing contents from the other (like it occurs with the WARP reading the auxiliary FATs of the PWRX in a secondary bank). But this is a bit too complex to use as a rule, so better stick to the first one.

I mentioned it before, this applies to the CL because it is the most flexible of all platforms. In the CL you can plug said configurations using the ROM images as you wish, for instance when you use the RAM or Flash locations you can plug the module pages straddling two ports.

Note that when using the IMDB mnemonic this issue is *sometimes* avoided based on the module size - but you're not completely protected either. Say for instance that you want to plug the HP-41 Advantage (41AD). If you choose page B that's also a port-straddling configuration and you're already pushing your luck a little, so rather don't!

This has nothing to do with being hardware-based or software-based emulation. In the DM41X case, it all depends on the MOD files settings. It's therefore also possible to run into this issue if the MOD file for a single-page ROM allows plugging it into the higher page within the port - and thus opening the possibility that the lower page of said port is used by another bank-switched module. This is BTW the preferred MOD setting, or otherwise you'll have blank holes in the I/O bus, as it occurs in the real machine when you plug two 4k-Modules in contiguous ports.

Finally, for the real HP-41 the bank-switching method is not implemented in the OS but in the module itself; so it is performed by the Advantage/HEPAX/ZEPROM chips when they "see" the proper instructions. This is mimicked by the CL at the ROM level and by the 41X at the MOD level (using the MOD file configuration), so it's obviously not performed by the plugged module since there isn't any.

PS.- A final comment about the locations used to plug certain modules: (not related to bank-switching). Remember that the YFNX must be plugged at a higher page number than the OS/X (or CCD-like ) for the extended catalogs to work. This is due to athe way the YFNX processes the I/O interrupt, masking it from the following ROMS in the bus.