Correct usage of VDP ports following the standard

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By sd_snatcher

Prophet (3646)

sd_snatcher's picture

17-06-2017, 15:06


And declare the device as for msx with expanded slots only compatible.

Could someone please explain all the fuss around the FCC1h not meaning just an expanded slot-0 anymore? All you have to do is to test only the bit-7 for all entries in the EXPTBL just like the documentation says.

With this, the following situations will arise when the machine has its BIOS relocated to a subslot in another slot:

1) If the machine has the slot-0 expanded, it there will be no colateral effects

2) If the machine doesn't have the slot-0 expanded, the only colateral effect will be that the contents of the slot-0 will appear mirrored in all "subslots":
- Software that search for ROM resources like the FM-PAC will just look for some extra slots as they would in any machines with expanded slots. Those extra copies of the internal mainBIOS wouldn't harm anyone.
- Software that search for RAM will behave exactly as in the Sony HB-10P, where the RAM is mirrored in slot-0 and slot-3.

Software that are written according to the guidelines won't have any issues with any of these cases. As I said before, the rules exist also to keep the hardware costs down, as it doesn't have to cover every possible situation that would have cost a lot of extra glue logic. We're talking about an 80's home computer here, not about PCs designed in 2017.

Are there any other cases that I might not be seeing?

By hit9918

Prophet (2927)

hit9918's picture

17-06-2017, 15:08

the topic is braintwist as hell
not because things crash all day, but because so many things work.

the idea "the bit 7 of fcc1 is slot 0 expansion at the same time".
neos always sets the bit even when both the slot 0 and the neos slot are unexpanded.
so one cant get it correct by how one plugs the cartridges in primary slot vs expander

interpreting it as slot 0 expansion, little msx1 got their slot 0 RAMs subslot-mirrored.
if the application got a problem with those slot 0 mirrors then the only way is to get the slot 0 expansion by asking the hardware.

By DarkSchneider

Paladin (989)

DarkSchneider's picture

17-06-2017, 15:49

Didn't know that point 1. I though the SlotId should have to be exact, including the expansion bit, or didn't work. So if slot 0 was expanded, and the new BIOS is set at slot 1 not expanded, the 10000001 SlotId at FCC1 would be incorrect to access new BIOS.

By hit9918

Prophet (2927)

hit9918's picture

17-06-2017, 16:00

neos sets bit 7 always to 1. reason unknown.
fcc1 must work with calslt to bios or else diskROMs crash.

By hit9918

Prophet (2927)

hit9918's picture

17-06-2017, 16:22

Sony HB-10P, in openmsx slotmap only page 3 is listed as mirror.
a lot more harmless case.

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