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VRAM test program
Posted: Thu Mar 22, 2001 5:25 pm
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I wrote a program to test a few things about VRAM access, that could be specific to the GG rather than the SMS. If somebody here could run it on a real SMS and Game Gear, I'd be very grateful. http://cgfm2.emuviews.com/demo/vramtest.zip If it works, three values will be printed to the screen. All I need to know is what the values are. The ROM is 32K, checksummed, and hopefully SDSC-compliant. :) |
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SDSC header blues
Posted: Thu Mar 22, 2001 8:46 pm
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Your year comes out as 20 00, which will resolve as 20 AD. The text offsets are misaligned by a byte. That causes my header reader to try and seek to FF05 and read beyond EOF :o( Looking at your .asm source, it looks like it ought to work, though. Maybe if you had ".db $22,$04,$01,$20 ; Date" it'd work? (My asm is sketchy at best.) Maxim |
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Re: SDSC header blues
Posted: Thu Mar 22, 2001 9:05 pm
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Yes, you've got it. With ".db $22,$04,$0120 ; Date", TASM will mask off the high byte of $0120 so it just assembles as $22,$04,$20. And so the rest of the header is off by one byte. |
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Re: SDSC header blues
Posted: Thu Mar 22, 2001 9:12 pm
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Yes, that seems to be it. In the asm file the .db statment is given $22,$04,$0120, and it is simply truncating the word-value $0120 to $20. Consequently, a byte is missing and the remaining fields are off by one. The fix Maxim suggests above will resolve the problem. Also, just a tiny little note to Charles, the month should be 3 (March) not 4 (April). -- Eric Quinn |
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Re: SDSC header blues
Posted: Thu Mar 22, 2001 9:27 pm
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Yes, I just noticed that. Anyway, I've updated my header reader to handle the problem a bit more gracefully. Maxim |
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Re: SDSC header twitches
Posted: Fri Mar 23, 2001 3:24 am
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ROM Offset 0x7FE8 (2 Bytes): Year (BCD) (Little-endian: 0x01 0x20 for 2001)
little-endian?!? sms/zilog is big-endian, motorola is little endian. I would hence like to propose the following motto for SDSC hereafter: SDSC. taking standard out of standard development he he he a s out. |
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Re: SDSC header twitches
Posted: Fri Mar 23, 2001 3:38 am
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You've got it backwards: Little Endian means "Little End First". (from Gulliver's Travels, the "Little Endians" cracked their eggs at the little end, the "Big Endians" cracked their eggs at the big end. No I never read it myself). And the z80 in the SMS is little endian. |
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Re: SDSC header twitches
Posted: Fri Mar 23, 2001 5:42 am
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I was refering more to the inconsistency with sega $7FF0 header - the rest was off the top of my head and mixed.
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Fixed test program
Posted: Fri Mar 23, 2001 6:32 am
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Thanks to Maxim and Eric, I've got the SDSC header fixed. And most importantly, I changed the text output so it can actually be seen on a Game Gear as well. Funny how these small details escape one's mind. :) The updated program is here: http://cgfm2.emuviews.com/demo/vramtest.zip Hopefully this will work. |
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Re: SDSC header twitches
Posted: Sun Mar 25, 2001 7:06 pm
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1.) The Z80 and SMS are little-endian. Please get your facts straight (especially before insulting me personally, and SDSC in general). 2.) Because of this, I (the SDSC tag format drafter) thought it would be better for the SDSC tag to use little-endian format, (and not big-endian which is not the native data storage format for SMS/GG machines), regardless of what the original SMS/GG header did (which the SDSC has no control over). 3.) The proposal was open for revisions for several weeks. If you had a suggestion you should have spoken up earlier. The tag format has been ratified. -- Eric Quinn |
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PolestaR
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Hmmm
Posted: Mon Mar 26, 2001 5:24 am
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What is this program actually testing? read/write commands? Has anyone tested it and supplied you with any info that is helpful? :)
-Jason Starr- |
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Re: Hmmm
Posted: Mon Mar 26, 2001 4:18 pm
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It tests a (possible) difference in doing VRAM writes with bit 15 set of the command word between the Game Gear and SMS. The only known game to do this is Ax Battler (GG), but it only uses it for a specific address range. The test program tries other addresses which may or may not be valid. Nobody has tested it yet - but then again no one is obligated to do so. :) |
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