mapped roms and page 0

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By Victor

Champion (468)

Аватар пользователя Victor

28-02-2019, 04:00

ARTRAG wrote:

Anyway I would have expected to see the other two banks, those at 8000h-BFFFh...
Are you sure that you are looking at those at 4000h-7FFFh?

Yes.. sure... in 0000h->41h,0001h->42h... for example... and changing the bank (writing in 6000h) the same you see in (6000h-8000h), is found in (2000h-4000h)

Maybe we should test with other mappers (KONAMI SCC, ASCII8...)

By Victor

Champion (468)

Аватар пользователя Victor

28-02-2019, 05:52

Now tests with real Salamander cartridge (SCC mapper):

A relevant difference:
(8000h-Bfffh) mirrored in (0000h-3fffh)

By ARTRAG

Enlighted (6240)

Аватар пользователя ARTRAG

28-02-2019, 08:03

And again you can control banks only if you access to 9000h and b000h, can you ?
Anyway, even if swapping banks is a bit complex, this feature opens to a layout where you have:
- rom in almost static banks at 0000h-3FFFh
- rom in easily swapped banks at 4000h-7FFFh
- 32KB of adjacent ram in 8000h-FFFFh

By gdx

Prophet (2984)

Аватар пользователя gdx

28-02-2019, 08:02

All mirror are indicated here:

https://www.msx.org/wiki/ROM_mappers

Most have been verified on real hardware. Otherwise, it is a cross of several informations.
By cons mirrors of Konami mapper clones can be different.

By ARTRAG

Enlighted (6240)

Аватар пользователя ARTRAG

28-02-2019, 08:26

gdx wrote:

All mirror are indicated here:

https://www.msx.org/wiki/ROM_mappers

Most have been verified on real hardware. Otherwise, it is a cross of several informations.
By cons mirrors of Konami mapper clones can be different.

I do not see any information about mirroring the rom content in memory pages different from 4000h-7FFFh in that wiki page (nor elsewhere in the net). Where should I look for them?
:-?

By gdx

Prophet (2984)

Аватар пользователя gdx

28-02-2019, 08:36

Look better (at the column "Page").

By ARTRAG

Enlighted (6240)

Аватар пользователя ARTRAG

28-02-2019, 08:37

gdx wrote:

Look better at the "Page" column.

Found! Thanks! And it matches with Victors findings.
This is interesting, because in openmsx I wasn't able to make it work, it shows FFh no matter of what I put in the rom and in the bank registers. I'll open a feature request :-)

By gdx

Prophet (2984)

Аватар пользователя gdx

28-02-2019, 08:59

Several other Rom mappers have probably same mirrors but I can not verify so nothing is indicated. If someone can check missing mirrors, update the wiki please.

By zPasi

Champion (444)

Аватар пользователя zPasi

28-02-2019, 12:51

Typically address line A14 is not connected and that causes the mirroring. So the range 0 - 3FFF refers to the same address space than 4000 - 7FFF. Also 8000 - BFFF and C000 - FFFF are the same. But the latter seldom has any use, usually you don't switch off the system RAM Wink

MegaFlashroms may also have A14 connected. If it is, mirroring probably doesn't occur.

By ARTRAG

Enlighted (6240)

Аватар пользователя ARTRAG

28-02-2019, 14:13

If the A14 line is not connected you should be able to see always the same thing in 0000-3FFF and 4000-7FFF
This doesn't happen always

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