Autor
| 4MB memory
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NYYRIKKI
msx master
Mensajes: 1503 |  Publicado: Mayo 10 2007, 09:29 |
Every once in a while I hear that 4MB memory mapper is problematic and there is plenty of software that does not work with computers with this much memory.
As I don't have this kind of configuration I would like to ask if someone here knows what actually is causing the problem? I know the MSX tR internal mapper missing bits and stuff, but I'm thinking now normal MSX2.
Can someone give me examples of software titles that do not work with 4MB memory?
Can someone explain the technical side, what is going wrong?
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Vincent van Dam
msx addict
Mensajes: 372 | Publicado: Mayo 10 2007, 09:53 |
The problem is a common bug in most software that counts the amount of available pages in the memory mapper. Usually an 8-bit register (eg. A) is used to store the number of pages; if the memory mapper is 4MB the 8 bit register will overflow => 0 available pages.
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pitpan
msx master
Mensajes: 1368 | Publicado: Mayo 10 2007, 10:03 |
Then, the problem is related to software rather than hardware, isn't it?
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Vincent van Dam
msx addict
Mensajes: 372 | Publicado: Mayo 10 2007, 10:37 |
Yes, it's a software problem.
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Ramones
msx novice
Mensajes: 30 | Publicado: Mayo 10 2007, 12:10 |
Dos 2.31, have a bug with this.
Count 255 segments, 4080k.
Nestor Soriano, (konamiman) have a great perfect routines for check memory in MSX, without the bug. (Only for DOS1, direct access to memory ports).
It's strange ... bios of Turbo R, count memory ok. Dos 2.31 bad coders... 
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NYYRIKKI
msx master
Mensajes: 1503 | Publicado: Mayo 10 2007, 12:19 |
I just wonder that if the mapper size is 4MB then last page you can use is 256-1 The overflow in this case does not matter. It is hard to imagine that there is a easy and common way to do this all wrong, but I guess I just think the issue some way differently.
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Vincent van Dam
msx addict
Mensajes: 372 | Publicado: Mayo 10 2007, 13:18 |
This posting is about the same issue http://www.msx.org/forumtopic4600.html
mth wrote:
Quote:
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There is actually a good reason to use only 512K in a turbo R: with more memory, programs that read the memory mapper register will fail. That includes the horrible hack known as MAP.COM. Unless you put in a different memory mapper in the turbo R configs of course.
Also some poorly written programs cannot deal with multiple mappers or even any mapper that is not in slot 3. So an additional mapper cartridge is not the same as more internal memory. On turbo R the internal mapper will always be the primary mapper (because it is faster) and some programs only use the primary mapper.
So I think the ideal boosted turbo R would have 2MB inside (some programs have problems with 4MB because they store the number of banks in a byte -> overflow) and the mapper implementation as found in for example the Philips NMS series, not the turbo R mapper which is not fully readable.
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nikodr
msx addict
Mensajes: 453 | Publicado: Mayo 10 2007, 13:59 |
I have an external memory mapper of 4mbytes.I checked symbos and works great although maximum ram it can support i think is only 1 mbyte.Is there some other software that would give me problems?I only have dos 1 by the way so memory mapper is not always preselected
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msd
msx professional
Mensajes: 608 | Publicado: Mayo 10 2007, 17:49 |
I've 4MB for years... only UR doesn't work.. most stuff just does. Some people make a big problem of this, but it just isn't and if stuff doesn't work it's easy to fix.
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Jipe
msx freak
Mensajes: 185 | Publicado: Mayo 10 2007, 20:03 |
i have a 8280 with 4Mo internal mapper and dos 2.30
problem in software are not the mapper but with the Dos 2
whith Dos 1 no special problem except some cracked version with loader basic
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msd
msx professional
Mensajes: 608 | Publicado: Mayo 10 2007, 20:12 |
I don't have a dos2 problem with it. dos1 has no mapper support at all, so it doesn't care about it
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Ramones
msx novice
Mensajes: 30 | Publicado: Mayo 10 2007, 21:02 |
Hmm ... the problem with Dos 2 is the counter. Dos 2 only "see" 255 segments = 4080k <> 4 Mb.
The second problem is Turbo R. If you have a "hypothetical" Turbo R with 4 Mb internal memory mapper, Dos 2.31 crash. This problem is only for Turbo R and 4 Mb.
My (in progress) MMC driver for LPE Cards or Young Seo cards, fix this problem. You can run DOS2.31 in Turbo R with a external memory mapper like as "primary" mapper, even 4 Mb memory mapper.
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manuel
msx guru
Mensajes: 3382 | Publicado: Mayo 10 2007, 21:30 |
Some cracks read the mapper registers and also detect 0 in stead of 256. This is of course illegal and unreliable anway, but it's a fact that it happens and that those things will fail.
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msd
msx professional
Mensajes: 608 | Publicado: Mayo 10 2007, 22:21 |
well that it only sees 4080KB is hardly a problem.
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msd
msx professional
Mensajes: 608 | Publicado: Mayo 10 2007, 22:22 |
Don't blame hardware for bad software
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