RAM between slots 0-0 and 0-2

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By Shinobi

Expert (128)

Shinobi's picture

29-08-2020, 12:23

Hi..

I know now that the problem of loading games from MSX2CAS or Caslink3 or SofaCAS is becuase some converted ROM games are bloaded at &h4000 which in my MSX AX-200 is in slot 0-2 (which is not visible at the moment when turn on the machine)

My question is how MSX2CAS or Caslink3 be modified to may be activate slot 0-2 RAM so that when Bload "CAS:",r is run, it will load the data into RAM correctly and run the game.

Let me explain what happens...

1. we use msx2cas to convrt rom to wav..

2. From basic we write bload"cas:",r and press return

3. We play the wav file from pc..

Now on machines with ram being on slot 0-0 and slot 0-2, how can we make basic bload the data to the correct ram address???

your help is very appreciated

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By Manel46

Hero (601)

Manel46's picture

29-08-2020, 13:25

When starting the MSX, the basic interpreter is located at address 4000h. Never the ram.
On Sakhr AX-200 wiki:
https://www.msx.org/wiki/Sakhr_AX-200#Slot_Map
It is seen that it does not have the ram in a linear way. That is, the upper ram is in slot 0 subslot 0, while the lower one, the hidden one, is in slot 0 subslot 2.
Some chargers do not take this into account.

By Shinobi

Expert (128)

Shinobi's picture

29-08-2020, 13:25

Even when booting into International mode, you have from 0000 to 8000 BASIC
And 8000-ffff you have slot 0-0 RAM

So what should be done on MSX2CAS or Caslink to make it work??

By Manel46

Hero (601)

Manel46's picture

29-08-2020, 13:53

That is, from 8000h to 0ffffh, we have the upper ram where the basic works.
The ram from 0 to 7fffh, is hidden. In these addresses is the bios (0 3fffh) and the basic interpreter (4000h 7fffh).
I had this same problem in the late 80's, with my Toshiba HX-20, until I ended up modifying the chargers, with what was convenient. It was when I learned a little about asm.
Port 0a8h handles the slots, and 0ffffh handles the subslots

By gdx

Prophet (3813)

gdx's picture

29-08-2020, 14:56

You have 3 solutions.

1/ Modify RAM search routine of the loader (It can be complicated)
2/ Cut the slot 0-0 select signal of upper RAM and replace it by the slot 0-2 select signal
3/ Insert a Memory mapper cartridge MSX1 compatible and use BMMS

(Do you have a picture of the motherboard?)

By gdx

Prophet (3813)

gdx's picture

29-08-2020, 16:15

The third solution might not work due to a bug in BIOS that causes a crash in some cases when RAM from 0000h to 7FFFh is in slot 0-x.

By Manel46

Hero (601)

Manel46's picture

29-08-2020, 19:28

Also in the boot of a 32 Kbs rom, there is a routine to enable page 2 of the rom.
This is another problem. I remember patching this too, with zeros (nop).

By Shinobi

Expert (128)

Shinobi's picture

29-08-2020, 21:39

What can be done from msx2cas program to solve this issue???

By Shinobi

Expert (128)

Shinobi's picture

30-08-2020, 00:25

Here is a picture of my motherboard

https://ibb.co/0CvYcYZ

By Manel46

Hero (601)

Manel46's picture

30-08-2020, 00:29

Nothing alone with this program. Obviously it contemplates that the ram is in a linear way, just like in the cartridge, the rom.
You should see the loading binaries and adapt them to the ram map of your computer.
Then delete the search for page 2 from the rom.
I understand that something difficult, if you do not know asm.
Get a MFR SCC + SD or similar, and you will load any rom. Smile

By gdx

Prophet (3813)

gdx's picture

30-08-2020, 01:54

Manel46 wrote:

Get a MFR SCC + SD or similar, and you will load any rom.

Yes, if you take the version with 512kB. MSX-DOS2/Nextor selects the largest mapper and therefore the majority of games should work. This kind of interface is a bit expensive but the best.

Seeing the motherboard, your MSX seems use the same board as this:
https://www.msx.org/wiki/Alexey_1024KB_Expansion_RAM

May be it's possible is to change it. (ask Alexey if it's possible for your MSX)
If that is the case, you can upgrade your MSX to MSX2 easily.

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