turbo R support

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Par snout

Ascended (15187)

Portrait de snout

30-04-2004, 23:36

A=2 blocks writing access to that part of the memory that is used to shadow the ROM, which indeed consumes some RAM memory.

Par flyguille

Prophet (3028)

Portrait de flyguille

30-04-2004, 23:39

how much without shadowing, how much shadowing?

Par Sonic_aka_T

Enlighted (4130)

Portrait de Sonic_aka_T

30-04-2004, 23:44

so, if i support on the console command, a command like TURBO ON... than run that routine with A=2, that's all the needed to work?
Well, I wouldn't make any TURBO ON command for compatibility' sake. But yes, if you were to make a command for MSX BASIC, all you would need to do is run this code with the appropriate register values. Ofcourse you would have to figure out how exactly the DRAM part is done. This is, I guess, somehow hardwired into the system. You would have to see how it would be possible to replace the original BIOS data with your MNBIOS data. I suggest you use an emulator for that part. I don't know if anyone has ever tried something like this, but I haven't.

copy to DRAM, you mean you use the main RAM memory?
Yep, the upper x pages of the MAIN RAM.

anyway, i are confused, A=1 and A=2 do blocked the writing access ?
Yes, like snout said, in R800 DRAM mode the pages to which the ROM is copied can no longer be accessed. You can try to write to them, but nothing will actually happen. This is only the case for R800 DRAM mode. In normal R800 mode the memory is all free like on any other MSX.

Par Sonic_aka_T

Enlighted (4130)

Portrait de Sonic_aka_T

30-04-2004, 23:45

how much without shadowing, how much shadowing?
Don't know... Prolly the BIOS and the extended ROM. I'll try and see if I can find out somehow... I'll get back to you about that...

Par Sonic_aka_T

Enlighted (4130)

Portrait de Sonic_aka_T

01-05-2004, 00:51

It seems to be the 4 highest pages of RAM. Both BIOS and BASIC ROMs are copied.

Par Sonic_aka_T

Enlighted (4130)

Portrait de Sonic_aka_T

01-05-2004, 01:21

the mirror of the BIOS on DRAM is made automatically or need be done on the boot by software?
I think the reset routine does the copying, but I'm not sure... What I don't know is if you can change the amount of segments (I checked, it's 4) can be changed somehow.

Par BiFi

Enlighted (4348)

Portrait de BiFi

01-05-2004, 08:17

You can't change that. There's always 64 KB at the top reserved for the following ROM's:

  • BIOS ROM (slot 0-0, page 0, copied to mapper page -4, $FC)
  • BASIC ROM (slot 0-0, page 1, copied to mapper page -3, $FD)
  • SUB-ROM (slot 3-1, page 0, copied to mapper page -2, $FE)
  • KANJI BASIC ROM (slot 3-1, page 1, copied to mapper page -1, $FF)

Even though the KANJI BASIC ROM is 32 KB (page 1 and 2), only the first 16 KB is copied to RAM.

Par BiFi

Enlighted (4348)

Portrait de BiFi

01-05-2004, 08:25

>>anyway, i are confused, A=1 and A=2 do blocked the writing access ?<<
Yes, like snout said, in R800 DRAM mode the pages to which the ROM is copied can no longer be accessed. You can try to write to them, but nothing will actually happen. This is only the case for R800 DRAM mode. In normal R800 mode the memory is all free like on any other MSX.
Like snout said?!? Excuse me, but if you're that narrowminded to refer to posts just on the same page, then ehrm... never mind. Wink

To correct things. You can also write the mapper pages used to mirror the ROM blocks in R800 ROM mode (A=1). Only when DRAM mode (either R800 DRAM or the tricksetable Z80 DRAM) is set, the system will write-protect those upper 4 blocks.

Par BiFi

Enlighted (4348)

Portrait de BiFi

01-05-2004, 08:36

How this is all hardwired, I don't know. You'd really need the technical docs and schematics to see, which as far as I know no-one has... Crying But, it works... Yeh! SmileEven that's pretty simple to explain. There's a 4 MB-sized mapper in the MSX turbo R. In that mapper range there's all ROM (except for the KANJI FONT ROM), SRAM and RAM. You can access that complete range in slot 3-3. This slot is usually used by the internal software: MSX Word Processor and in the GT there's MSX-View. Since the RAM is covered by that mapper as well and the mapper having access (or at least, it seems that way) over several slots, it can change the particular pages containing either ROM or RAM to those particular slots and pages.

Par Sonic_aka_T

Enlighted (4130)

Portrait de Sonic_aka_T

01-05-2004, 12:02

Like snout said?!? Excuse me, but if you're that narrowminded to refer to posts just on the same page, then ehrm... never mind. Wink
Dude?!?

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