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MiSTer-devel / MegaCD_MiSTer

Mega CD for MiSTer
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MegaCD CPU possibly running too slow. #24

Closed SegaSnatcher closed 4 years ago

SegaSnatcher commented 4 years ago

NeoDev recently ran a CPU test comparing a Pal Mega CD and the MiSTer core at 50Hz and it appears the MiSTer MCD core is running a bit slower.

Here is the results from a real Mega CD.

IMG_20191211_200235

Here is the results from the MiSTer core.

IMG_20191211_200631

Here is where you can find the test rom.

http://gendev.spritesmind.net/forum/viewtopic.php?f=8&t=2981&p=34888

sorgelig commented 4 years ago

i've saw that thread - there was so many versions of this test with different results. Hard to trust this test. Is there a game affected?

SegaSnatcher commented 4 years ago

Yes, many people believe this is the reason why Sonic CD has more slow down than real hardware.

Granted Sonic CD has some slow down on real hardware, but many people are pretty convinced that it happens even more on the Mega CD core, and those CPU tests kinda gives weight to this assumption.

SegaSnatcher commented 4 years ago

Someone I talked to believes the CPU slowdown is caused by the fact that the two CPUs have to go through the single SDRAM board for access.

sirblew commented 4 years ago

Someone I talked to believes the CPU slowdown is caused by the fact that the two CPUs have to go through the single SDRAM board for access.

Does using the DDR memory option help? You can do this in the Genesis/Megadrive core but I'm not sure about MegaCD.

SegaSnatcher commented 4 years ago

Someone I talked to believes the CPU slowdown is caused by the fact that the two CPUs have to go through the single SDRAM board for access.

Does using the DDR memory option help? You can do this in the Genesis/Megadrive core but I'm not sure about MegaCD.

Pretty sure MegaCD core requires ram board.

sorgelig commented 4 years ago

1) CD games don't use ROM(Cartridge) besides the BIOS. 2) The test rom is not really correct in CPU speed measure. 3) Recent source already has changes which "fixes" this buggy test rom.

SegaSnatcher commented 4 years ago
  1. CD games don't use ROM(Cartridge) besides the BIOS.
  2. The test rom is not really correct in CPU speed measure.
  3. Recent source already has changes which "fixes" this buggy test rom.

Which recent source? Do you mean a commit?

sorgelig commented 4 years ago

yes, there was commits since latest release.

SegaSnatcher commented 4 years ago

Looks like its testing correctly now.