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That 6.3K is shared between all channels, there is single (slow) bus.
As for MD VDP, you got 2 halves of the command word.
One half is like SMS - 2 bits for type, 14 bits for VRAM address
Other half is new to MD with 2 more adress bits to get 64KB VRAM and some more type bits to accomodate for new memories and modes
You need to send it 32bits of information as a command, but you don't send it in one go. You write two 16bit values.Quote:
Originally Posted by sheath
Just like TmEE said. The SMS had a 16bit command word for VRAM access. But you can't fit a 16bit address if some of the bits in the command word are used. Two bits were used for register select and 14 bits were used for the vram address. The VDP has 64kbytes of vram, so you need more bits. And since the VDP only takes word writes to the ports (you can do byte writes but the upper byte will be a duplicate of the lower written byte, and written as a word). So, you send one 16bit command followed by a second 16bit command. There's a special setting in the VDP upon a specific register set, that expects more data to follow. Nothing more, nothing less. It's not different really than the VDC in the PCE/TG; if you want to write to vram then you need a 'register' followed by a 16bit address (that means you need to write two WORDS, but the VDC lets you get away with only writing lower byte of a reg select so 24bits if you want to get technical, but then you need to another reg to enable the write, so you're back up to 32bits total). Like I said, this isn't a big deal. It doesn't gain any benefit or fall into some 32bit classification because of this.Quote:
Originally Posted by sheath
I mean, it's not like arguing the 68000 is 32bit. That argument at least has some merit. Not even the Neo Geo guys went there though with their '24-bit', let alone Sega with their blast processing campaign.
Yes, divide by 8 if you're using all 8 channels. The SNES has two separate bus; A bus and B bus. One is for the cart and one is for the PPU port and regs (which also handles the indirect port into far ram IIRC). The transfer rate is 8 master cycles which is 2.68mhz which is 2.68mbytes per second which is 166bytes per scanline. The DMA can't read faster than 8 master cycles on the cart bus and system ram (even if the cart has fast-rom which is 6 master cycles). So if two channels are competing for the same cart bus, the access is interleaved between whatever channels are used.Quote:
I had a document on this that doesn't seem to be available anymore. It said 2.68MB divided by 8 (channels) divided by / 60 (frames per second), DMA occurs during VBLANK, according to the Super NES Programming/SNES Specs, Direct memory access unit. I will take some more time and look at Anomie's Register Doc to see how the 166 byte per scanline works out.
The Neo Geo is INDEED 24Bit, it says so on the box however if SNK released their Bios revision update via Memory card slot expansion it would have been the worlds first "48-Bit" machine back in 1995 but got cold feet from the announcement of the "Ultra 64".Quote:
Originally Posted by tomaitheous
Ohhhhhhhhhhhhhhh What could have been......
Yeah, and having it broken down to a smaller pipeline is pretty much where I would draw the line anyway. It sounds like the other capabilities of the VDP are much more important than the fact that it takes two 16-bit Words to start an operation.Quote:
Originally Posted by tomaitheous
If the CPU does 32-bit calculations internally, and it does, then it is at least capable of 32-bit calculations. We know that doesn't necessarily mean much, it's just a technical fact relevant to programming.Quote:
Originally Posted by tomaitheous
It still isn't adding up for me. 2.68MB is 2744.32 KB, divide that by 8 channels and then by 60 Frames and I get 5.72KB / frame. I also don't know what it means that DMA can only occur during HBLANK or how that compares to the Genesis VDP. Also, does all 8 channels need to be used to transfer the maximum amount of data per frame?Quote:
Originally Posted by tomaitheous
Doing it the way you did, 38 * 166 bytes = 6.16KB. Yeah, I'm lost.
If the Neo Geo is 24-bit, so is the Genesis. They both have a 68000 and Z80... 16 + 8 = 24... SNK's very own marketing right there.Quote:
Originally Posted by evilevoix
MHz does NOT equal MB/sec. 2.68MHz => 2680000 bytes per second. Think, hard drive units. :DQuote:
Originally Posted by sheath
That figure is also PAL, not NTSC... 2680000 / 8 / 50 = 6700 bytes/sec.
http://www.youtube.com/watch?v=K9PhKD85e78Quote:
Originally Posted by evilevoix
Okay, so NTSC would be 5583 bytes per frame. Or for NTSC/PAL comparison it would be 5.45KB/6.54KB respectively.Quote:
Originally Posted by Chilly Willy
Now what am I missing?! ;)
No. Mira, the master clock of the SNES is 21.47727mhz. There's DMA and there's HDMA. They are not the same, but they will use the same 'channels' - but HDMA only runs during active display. Forget HDMA for now. So DMA only runs during vblank. The speed of DMA (and HDMA) to copy a byte from the cart bus to the A bus is 8 master cycles (regardless if you have fast rom installed on the bus which is 6 master cycles). 8 master cycles is 21.47727 / 8 = 2.68465875mhz. If all you had was vblank or the display was disabled, you could transfer 2,684,658 bytes per second. But that number is kind of useless since we want specifically for vblank periods.
Ok, assume vblank is 38 scanlines long (224 vertical display setting). How many master cycles are in a scanline? Easy: 21,477,270 / 60 = 357,954.5. So there is 357,954 master cycles per frame. 357954 / 262 = 1366 master cycles per scanline. Since the DMA speed is fixed at 8 master cycles per byte; 1366 / 8 = 170.78 bytes per scanline. 170.78 * 38 scanlines = 6.49k per second. That number doesn't equal 6.3k, but if you subtract 1 scanline from 38, then 37 * 170.78 = ~6.3k. My numbers might be slightly rounded or such, but anyway that's the math for it.
@sheath If you really want the most in depth details about the SNES, I recommend contact byuu in one of the forums he hangs out. He wrote the most accurate SNES emulator to date and attention to detail is his thing.
Don't divide 2.68mhz by 8. It's 8 master clock cycles, *not* 8 cpu cycles.
Yeah, the bitness of the VDP means nothing - really. What if you learned that the VDP was built all on 4bit chained logic? It wouldn't change anything 'cause you've played the Genesis and have seen what it can do. It's fun to talk about specs in relation to what can be exploited for the system's advantage, but most of that stuff has already been figured out on both systems. The only thing left to wow gamers on the Genesis is homebrew softs with really good graphic art that looks like it goes beyond the color limitations. And for the SNES, games that appear to tap that 'hidden' speed potential of the stock CPU. Else, it's all been done on both systems. Well, maybe samples on the Genesis but TmEE's got that one handled. That's pretty much why I dev mostly on the PCE/TG16. It had quite a bit of potential that wasn't shown off. So, I get more bang for the buck (my effort) than on other systems. Plus, I love the challenge of the limitations it does have in relation to the SNES and Genesis. So it hits both my coding g-spots :P But I digress...Quote:
Yeah, and having it broken down to a smaller pipeline is pretty much where I would draw the line anyway. It sounds like the other capabilities of the VDP are much more important than the fact that it takes two 16-bit Words to start an operation.
tomaitheous, where can we see some of the stuff you have coded for the PCE?. Are you eventually gonna make a game for it?. Sorry, i dont know much about your background. Could you mention some examples of the "unshown potential" of the PCE?.
The Saturn was first marketed in Japan as a 64bit machine because it had 2 x 32bit cpus. Though by that logic it may as well have been over 200 bits if you count video hardware, scu dsp, the 68k, and the sound chip...Quote:
Originally Posted by Guntz
The Genesis did not have the Bios to properly marry the "Bittness" of the two chips properly. So unfortunately it is a proper 16 Bit machine but nothing more.Quote:
Originally Posted by Guntz
What . Eternal Champions has some of the most God afwul music and sound effects one can hear on the Mega Drive and so tinny it makes ones ear drums shake to the core. Yes Toe Jam & Earl had great music and sample sounds ; but it didn't do simultaneous samples has some sample would play the other would be cut out Streets of Rage II also had this issue so did Greatest Heavyweights thanks to the limits of the Mega Drive chip .Quote:
Originally Posted by sheath
Oh no... not more demo's and Youtube ? Play the real games on real hardware and hear the difference. Even the Amiga out did the Mega Drive when it came to sound and colour and that came out years before the Mega Drive . SEGA could and should have done better with the MD colour pallet and sound sample - But all machines had their pro's and consQuote:
Then explain Tiidos sound engine that gets 2 PCM channels working perfectly
You don't know much about computers, do you?Quote:
Originally Posted by evilevoix
Those Youtube videos are recorded off of real hardware if they're from Tiido or me.Quote:
Originally Posted by Smilebit.. errr I mean Team Andromeda