Search found 256 matches

by TascoDLX
Wed Feb 09, 2011 9:09 am
Forum: Mega/SegaCD
Topic: Savestate format and Lunar too
Replies: 5
Views: 4002

Re: Savestate format and Lunar too

If the CD audio tracks are not loaded, it won't work. Shouldn't be any problem if all the files are named correctly, though. Anyway, I was looking at the save state file and it has the GST tag at the beginning. Anyone have information for the CD part of this format? For Fusion? I have this: 0x22478:...
by TascoDLX
Fri Dec 31, 2010 4:45 pm
Forum: Video Display Processor
Topic: VDP VRAM access timing
Replies: 36
Views: 30818

A minor gripe: The manual says the maximum wait time for VRAM writes (to a full FIFO) is 4.77us in H40 mode. Let's see: SC in H40 mode is MCLK/4, outside of H-sync. Because of the refresh cycle, there's a gap of 16 access slots between external access slots. So, that's a maximum wait time of 4/MCLK ...
by TascoDLX
Thu Dec 30, 2010 10:01 pm
Forum: Megadrive/Genesis
Topic: Mickey Mania emulator comparison
Replies: 67
Views: 32528

Thanks to Nemesis's discoveries about VRAM access ( that post ), the effect is pretty much explained. To change a whole palette (16 word entries) on one line, the display is disabled, the palette data is DMA'd to CRAM, then the display is reenabled. Obviously this is done during the H-blank period a...
by TascoDLX
Thu Dec 30, 2010 9:50 pm
Forum: Video Display Processor
Topic: VDP VRAM access timing
Replies: 36
Views: 30818

Awesome, Nemesis! Can't wait for more. :D
by TascoDLX
Thu Dec 23, 2010 3:47 am
Forum: Mega/SegaCD
Topic: Sub-CPU Jump Addresses
Replies: 4
Views: 3699

Some games, like this one, are quite friendly, allowing you to simply provide a filename and have that file loaded where you want it. Some games will index their files in a separate table, bypassing the ISO directory entirely, so that files are referred to by number, not name. It varies. You can pro...
by TascoDLX
Wed Dec 22, 2010 12:24 pm
Forum: SGDK
Topic: make a Soft Reset with Gendev
Replies: 16
Views: 6371

Note, if you want to do a proper soft reset, you'll need to reset the stack pointer.

This should work:

Code: Select all

asm volatile ( "move   #0x2700,%sr\n\t"
               "move.l 0,%a7\n\t"
               "move.l 4,%a0\n\t"
               "jmp    (%a0)" );
by TascoDLX
Wed Dec 22, 2010 10:41 am
Forum: Mega/SegaCD
Topic: Sub-CPU Jump Addresses
Replies: 4
Views: 3699

Re: Sub-CPU Jump Addresses

Anyway, I'm good on BIOS calls, but what would a jsr to $7880 or $7800 do. I can't seem to find that anywhere in these documents but I see it several times in the (either IP or SP code, still figuring that one out). SP (subcpu boot code) loads to $6000, so it's probably right there. $7800 @ loc_280...
by TascoDLX
Tue Aug 31, 2010 8:36 am
Forum: Mega/SegaCD
Topic: Small Sega CD PCM question: sample rates
Replies: 12
Views: 8780

The PCM address registers each have an 11-bit fractional component (2^11 = 2048). Technically, the sampling rate is fixed at 32KHz, and FD serves as an increment to the address register. In a sense, you could say that a PCM RAM pointer is advanced by FD/2048 bytes at every clock (32KHz). So, if FD =...
by TascoDLX
Sat Aug 28, 2010 3:01 am
Forum: Mega/SegaCD
Topic: Small Sega CD PCM question: sample rates
Replies: 12
Views: 8780

I have it as: Sample rate = FD * PCM clock / 2048, where PCM clock = 12.5 MHz / 384 = 32552 Hz approx.

SR = (FDH * 256 + FDL) * 12500000 / (384 * 2048)
by TascoDLX
Sat Jul 10, 2010 4:17 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

I basically just rearranged the VRAM code according to the tech memo: plenty of time between the last read and next setting the control reg. Didn't do much more than reorder the instructions, really. I made sure to spend at least 116 CPU clocks following each read sequence (consecutive reads are not...
by TascoDLX
Fri Jul 09, 2010 8:47 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

One last shot: hackpatch v3. Only fixes for hardware in this one.

Sorry, couldn't help myself. :wink:

I believe the tearing evildragon pointed out is caused by updating the scroll values midscreen. I didn't bother myself with that.
by TascoDLX
Wed Jul 07, 2010 12:32 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

Where was that memo hiding? :P So it seems the delay belongs after the last read. If you reorganize the code, you probably don't need any artificial delays (NOPs or such) -- just move anything you can between the last read and setting the address for the next write. But, using a buffer is a wonderfu...
by TascoDLX
Tue Jul 06, 2010 7:20 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

OK, I gave it a shot: hackpatch v2. Let me know if it's better.
by TascoDLX
Tue Jul 06, 2010 5:03 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

It's probably the VRAM reads/writes. The code does a bit of read and writeback. I'm thinking that setting the address and reading immediately may fail occasionally. I'm not sure about writing immediately. Anyway, it might be enough to have a NOP before the first read or write. I'm also thinking that...
by TascoDLX
Mon Jul 05, 2010 9:18 am
Forum: Demos
Topic: Super Mario Bros on the Genesis
Replies: 58
Views: 30616

The problem now is that inputs seems not to be read properly: my controller does not respond and I can't leave the menu screen , it's probably something related to timings when programming the controller. It's much more obvious than that. (hint: something is missing.) For anyone still "testing", he...