Mini demo / tech MD stuff posted by members :)

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sun Feb 24, 2008 6:08 pm

You can't BTST VDP !!! You need to read to reg, and BTST the reg otherwise the thing locks up... at least it has always happened on my MDs.

Jorge Nuno · Post by **Jorge Nuno** » Sun Feb 24, 2008 6:09 pm

Really!? I didn't knew that ...

OK it seems to be fixed now, sheesh!

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sun Feb 24, 2008 8:46 pm

Still doesn't work.....

Chilly Willy · Post by **Chilly Willy** » Sun Feb 24, 2008 9:18 pm

@Jorge - a little hint - remember that the 68000 is BIG ENDIAN. bit 1 of the byte at (a6) is the same as bit 9 of the word at (a6).

Jorge Nuno · Post by **Jorge Nuno** » Sun Feb 24, 2008 9:35 pm

Yeah, I was bittesting a byte, but now I'm not doing bittest anymore.
Now I'm moving the VDPstatus to D0, then I do ANDI.w #2, d0; so only the DMAbusy is preserved, then I do BNE to test the status again...

8bitwizard · Post by **8bitwizard** » Fri Feb 29, 2008 1:02 am

Jorge Nuno wrote:My method detects 65536B in the emus, instead of 2MB so I assume it's the way to go ... but I can't test on my MD because my RAMcart isn't ready...

That's because memory mirroring is a hardware effect that doesn't need to be emulated to make games work properly, and therefore is usually not emulated. In fact, it's more trouble to implement it in an emulator than to not implement it. On the other hand, it's easier to have mirroring in hardware, because that's fewer address lines to decode, and it doesn't matter that you can see the RAM in addresses that you won't use.

You can't use an emulator to develop hardware tests like that.

Eke · Post by **Eke** » Fri Feb 29, 2008 9:50 am

TmEE co.(TM) wrote:I directly streamed the BIN to my flashcart form the Internet... no go....
(actually re-DLed and flashed )

Leave the RAM check out.... maybe it works then ?

I tried it under genesis plus with debugging ON and here's what I get:

Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)

You are writing into ROM space, maybe it doesn't work with flashcarts ?

if you want to to some debugging without hardware, here's the version I use for personal testing
drop your bin file into gen.exe, it's a DOS executable but should work
error.txt give you informations about useless or illegal (will lock the machine) access

http://www.file-upload.net/download-697174/gp.zip.html

That's because memory mirroring is a hardware effect that doesn't need to be emulated to make games work properly, and therefore is usually not emulated. In fact, it's more trouble to implement it in an emulator than to not implement it. On the other hand, it's easier to have mirroring in hardware, because that's fewer address lines to decode, and it doesn't matter that you can see the RAM in addresses that you won't use.

I'm not sure to understand: are you talking about the fact that the 64KB or WRAM are mirrored between $e00000 and $ffffff ? this is emulated by most emulators..

how could a program detect 2MB of memory on the genesis ? I probably missed something

TmEE co.(TM) · Post by **TmEE co.(TM)** » Fri Feb 29, 2008 12:31 pm

Jorge has added extra RAM to his MD (I guess it was 256KB ?)... And to fool my flashcart, you need to write 4x RIGHT commands... otherwise it goes on with normal operation.

And thanks for the tool Eke

Eke · Post by **Eke** » Fri Feb 29, 2008 1:55 pm

.

Jorge has added extra RAM to his MD (I guess it was 256KB ?)

oh, I see

And thanks for the tool Eke

how dare you call this a "tool"

it's a fully functionning emulator, with the exact same features/compatibility of the GCN port... ok ok, it has no sound, no joypad support or filtered graphics because I have absolutely no competence in allegro/sdl/directx/etc and only use it to test my builds

but it should be pretty accurate and run every known genny roms flawless (please tell me if it doesn't, I love debugging roms

) :

TmEE co.(TM) · Post by **TmEE co.(TM)** » Fri Feb 29, 2008 2:24 pm

I found out that it is a emulator after DLing and finishing my post.... but emulator is technically a tool if you use it in dev process.

Chilly Willy · Post by **Chilly Willy** » Fri Feb 29, 2008 9:06 pm

Eke wrote: I tried it under genesis plus with debugging ON and here's what I get:

Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)
Unused write16 00000000 = 0002 (PC = 00000320)
You are writing into ROM space, maybe it doesn't work with flashcarts ?

Sounds like the memory test is going one loop too far making it test 0x1000000 (which is the same as 0x000000 in the Genny).

how could a program detect 2MB of memory on the genesis ?

As mentioned in another post, some folks have increased the amount of RAM in the Genny. I myself am looking at trying to boost the work RAM to 2 MB. It's mostly a matter of finding the right PSRAM parts, then replacing the RAM on the main board.

8bitwizard · Post by **8bitwizard** » Thu Mar 06, 2008 12:52 pm

Another thing to be careful about when doing a memory test is to not go outside the areas that get DTACK on a standard MD. Because there is no bus error circuitry, the system will lock up in those areas.

Even if your memory modification has DTACK, an unmodified MD will not have the DTACK and will still lock up.

Jorge Nuno · Post by **Jorge Nuno** » Thu Mar 06, 2008 8:29 pm

Default MDs pull DTACK low from E00000 to 0 (and onwards), that shouldn't be a problem...

mic_ · Post by **mic_** » Tue Aug 12, 2008 12:57 pm

I've got one here (source code here). It doesn't do anything advanced, but it has horizontal and vertical scrolling, sprites and music. And it works on a real Megadrive (at least the PAL version - I don't have an NTSC console to test on).

TmEE co.(TM) · Post by **TmEE co.(TM)** » Wed Aug 13, 2008 5:45 pm

Nice demo !!!

Tested and found to work on real HW in any config

what is XPMCK ?