wait states
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wait states
I'm curious if there's a way to halt the 68k to eliminate the additional wait states on the 32x side form accessing the bus. Somehow halt the 68k after the 32x initialize process? Be it hardware or not.
Or if there are any regions/areas in the address range that are remapped from the 32x unit when it is initialized - since it *is* the pass through for the cartridge. For the same idea above - to have access to ram/rom on the cart at same speed as internal SDRAM.
Or if there are any regions/areas in the address range that are remapped from the 32x unit when it is initialized - since it *is* the pass through for the cartridge. For the same idea above - to have access to ram/rom on the cart at same speed as internal SDRAM.
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Re: wait states
You won't have access to rom on the cart at same speed as internal SDRAM whatever you do. The ROM is 16 bits and very slow when you compare it to the SH2 memory capabilities. You should never avoid as most as possible to access ROM when you're doing "in-game" processing. The normal way is to load ROM data into SDRAM before a level start then never access ROM at "in-game" time.tomaitheous wrote:...
For the same idea above - to have access to ram/rom on the cart at same speed as internal SDRAM.
DOOM actually reads ROM data during 3D rendering, even worst it fetch its code from ROM, that partially explains the poor frame rate obtained...
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That's understandable - DOOM has WAAAAAAAAY too much data to fit hardly any into SDRAM. I'm fairly certain the only thing in SDRAM is probably screen buffers (DOOM uses more than 2) and sound buffers. The DOOM executable wouldn't even fit in the SDRAM. A small level MIGHT fit in the SDRAM (just the level data, not the patches, flats, sprites, or sounds).
That's the biggest problem when making a DOOM conversion for the 32X - severe lack of RAM. Most console make up for that by leaving code and most data in the ROM. Just the variables and buffers go into RAM.
That's the biggest problem when making a DOOM conversion for the 32X - severe lack of RAM. Most console make up for that by leaving code and most data in the ROM. Just the variables and buffers go into RAM.
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Re: wait states
Yep. It's also much slower than the SDRAM anyway, so even if it were 32 bits, it'd still be slower.Stef wrote:You won't have access to rom on the cart at same speed as internal SDRAM whatever you do. The ROM is 16 bits and very slow when you compare it to the SH2 memory capabilities.
Besides, I'm fairly certain that when the SH2s are reading ROM the 68K gets pushed aside, so there's no benefit in trying to stop the 68K.
Actually I think most games access ROM during the game. It's not too bad, unless...Stef wrote:The normal way is to load ROM data into SDRAM before a level start then never access ROM at "in-game" time.
Erk... that's nasty. I'm also pretty sure Sega tell you this is not allowed So DOOM is a bit naughty.Stef wrote:fetch its code from ROM
Maybe, yeah. Still, I never understood why DOOM had such a small screen and such a low framerate. It should run way better than it did on a 486.Stef wrote:that partially explains the poor frame rate obtained...
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I take it then any access to the rom from the 32x is hard coded for slower memory interface than(fixed wait states)? That seems bazaar that they would not have a system/setting to change the wait states for faster ROMs.It's also much slower than the SDRAM anyway, so even if it were 32 bits, it'd still be slower.
Edit: Man.. I didn't see that the sVDP buffer has a latency of 3 cycles. Things are really looking bad on this design...
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SH2s were just too fast for the rest of 32X...
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