GX4000 upper rom at reset time.

[arnoldemu]

I have tested which cartridge page is visible in the range &c000-&ffff at reset time.

The important fact is that port dfxx is reset to 0 at this time.

Page 0 is always visible at &0000-&3fff.

On GX4000, page *1* is visible at &c000-&ffff, normally this is BASIC. It is not page 0 as I have previously assumed. DFxx=0 maps to page 1.
On Plus it depends on /EXP. It will either be 1 (normal) or 3 (and CPM should be autostarted as on CPC).

To be sure, you should always set dfxx to a specific cartridge page using bit 7 set, so you can be sure you get exactly the page you expect.

I have updated the arnold v documents to reflect this.

[arnoldemu]

On GX4000, if you do this:

Code Select Expand


ld bc,&df07
out (c),c


The GX4000 will select page 1, the hardware to active the disc page isn't active, so this will not select page 3 like it does on a Plus.

[andycadley]

Cool. Always useful information to know.

[TFM]

On GX4000, if you do this:

Code Select Expand


ld bc,&df07
out (c),c


The GX4000 will select page 1, the hardware to active the disc page isn't active, so this will not select page 3 like it does on a Plus.

Doesn't this depend on the Cartridge you use?

[arnoldemu]

Doesn't this depend on the Cartridge you use?

no.

gx4000 will always select physical page 1, how that maps to the actual rom itself can be different.

For example, if you had a 32KB cartridge ROM, then this would repeat through the cart ROM address space because some address lines are not used and so it will appear to do that.

If the same data was put onto a 512KB ROM with lots of empty space it would not appear to repeat.

[TFM]

Well, I had this case in mind: You use the Cart from the 6128 Plus for the GX4000... but maybe I got lost in translation. 

[arnoldemu]

Well, I had this case in mind: You use the Cart from the 6128 Plus for the GX4000... but maybe I got lost in translation. 

My confusion.

Yes you are correct.

So if you want a game to run on gx4000 AND plus, avoid using logical numbers (e.g. 0-127).
Only use physical numbers (128-255).

Plugging a OS cart into a gx4000 shows Basic prompt, selection menu doesn't exist because gx4000 will not recognise logical page 7 and activate amsdos.

[TFM]

Very interesting. Thanks a lot! Since recently so much GX4000 get sold, it may make sense to consider this machine even more as gaming target. 

[KaosOverride]

My confusion.

Yes you are correct.

So if you want a game to run on gx4000 AND plus, avoid using logical numbers (e.g. 0-127).
Only use physical numbers (128-255).

Plugging a OS cart into a gx4000 shows Basic prompt, selection menu doesn't exist because gx4000 will not recognise logical page 7 and activate amsdos.

So this makes no$cart converted games unusable on GX4000

¿Firmwre must be patched to activate the 128-255 range?

[arnoldemu]

So this makes no$cart converted games unusable on GX4000

¿Firmwre must be patched to activate the 128-255 range?

correct.

But also, I have found that many games can't be started from joystick. So if you could make a cart, it will run but you can't play the game!