SUGGESTIONS

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stephen_usher
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Re: SUGGESTIONS

Post by stephen_usher » Tue Aug 21, 2018 6:58 pm

exxos wrote:
Tue Aug 21, 2018 6:56 pm
stephen_usher wrote:
Tue Aug 21, 2018 6:47 pm
I was just wondering, given a lot of the slow-down for the ST is due to sharing the memory between the CPU and video sub-system, would a redesign using dual ported RAM for the screen memory be a good idea?
I already talked about adding ram to shifter a few posts up..
But surely that different to having dual ported main memory?
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Re: SUGGESTIONS

Post by exxos » Tue Aug 21, 2018 7:27 pm

stephen_usher wrote:
Tue Aug 21, 2018 6:58 pm
But surely that different to having dual ported main memory?
What options are there for dual port 16MB SRAM controlled by a PLD ?
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Re: SUGGESTIONS

Post by stephen_usher » Tue Aug 21, 2018 8:55 pm

I must admit that I don't know anything about the interfacability other than people on other projects mentioning it. If it's not possible then it's not possible. It was merely a thought as this is a suggestions thread.
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Re: SUGGESTIONS

Post by exxos » Tue Aug 21, 2018 9:04 pm

stephen_usher wrote:
Tue Aug 21, 2018 8:55 pm
I must admit that I don't know anything about the interfacability other than people on other projects mentioning it. If it's not possible then it's not possible. It was merely a thought as this is a suggestions thread.
Its a good thought, but I dont think its really possible. SRAM only has 1 IO channel, and that's what the new MMU core uses.. It would probably need a lot of work to get running and I can't redo the entire MMU in FPGA, only re-use suska code and add simple bits to it.. I will think about it though.. but even RAM "multiplexed" between CPU ^ SHIFTER, at 50MHz its going to rocket along anyway.
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Re: SUGGESTIONS

Post by chlu600 » Tue Aug 21, 2018 10:48 pm

One feature that I havn't seen in this topic is tile-based background graphics. I've always wanted such a feature in the ST/E. Because it opens up for both better games and interesting demo effects, see the C64-scene and their charater mode.
A shifter with small amount of video ram for those assets and some mapping data. Of cource with a seperate 16 colour palette and possibility to set vertical and horizonal offset by one pixels steps. The first color in the ordinary palette has background transparency if background is defined.

More of day dreaming - but useful back in the days I think 😃

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Re: SUGGESTIONS

Post by exxos » Tue Aug 21, 2018 10:53 pm

chlu600 wrote:
Tue Aug 21, 2018 10:48 pm
A shifter with small amount of video ram for those assets and some mapping data.
Thats what I was talking about earlier... shifter with video ram.. but loads of other stuff aswell relating to it... like with a frame buffer, you would have the option to only update parts of the frame, not the whole lot.. kinda like how video only updates bits which move. But Smonson is going to add more video modes, but would be a huge re-code and job to redo the shifter with its own RAM.

Its why I was more thinking manipulating the MMU instead.. at least a "quick wipe" could be done.. also dont forget the blitter will be running 50MHz as well...
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Re: SUGGESTIONS

Post by Petari » Wed Aug 22, 2018 9:24 am

exxos wrote:
Tue Aug 21, 2018 6:09 pm
As another thought.. the MMU itself could have some new functions built in.. for example a new register to quickly clear a block of ram... Once the CPU loaded start and end address, internal counters can clear the RAM contents very quickly internally. Had the thought while talks in other threads talking about fast clear of backgrounds for drawing next screen..
Blitter can likely do fast work with screen clear also as has direct access to RAM, but still takes some time to complete. Not sure how many cycles it would take to clear full screen area ? In anycase, internal MMU counters could do block clear faster and no need to use CPU or blitter for main work (only for address setup).
In case of normal ST at 8 MHz you can clear RAM very fast with proper CPU code - what is present even in later TOS versions. movem.l with all possible registers set to 0 will achieve close to 4 MB/sec . With blitter it can be some 5% faster. Other half of time is for video generation.
If accelerated Atari can keep that design that shares RAM access in ratio 50-50% between CPU (bus) and video, then clearing with CPU or blitter will be same efficient. MMU can be faster only if can perform RAM access during video blank periods (when no screen gen.) Then, it may be faster some 30% in clearing. Not too much. There is no lost time with CPU for address setup, because all it fits in RAM access time of 500nS (8 MHz) . Only lost time is fetching of instruction/opcode, and that's little when using movem .
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Re: SUGGESTIONS

Post by KyleB » Tue Aug 28, 2018 1:11 am

Been thinking a while about the ram being a falcon board. Not sure that's a good idea, I mean I get the basic principle - all falcs are 14mb these days it seems so why not recycle - but not sure that these 4MB boards are going to be all that plentiful anymore after 25 years of being chucked in the bin.

Is there not some 4MB ramchip that will work in an ST circuit? Or even just one 4mb simm, seems easy enough to find on ebay especially laptop stuff.

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Re: SUGGESTIONS

Post by exxos » Tue Aug 28, 2018 8:21 am

KyleB wrote:
Tue Aug 28, 2018 1:11 am
Been thinking a while about the ram being a falcon board. Not sure that's a good idea, I mean I get the basic principle - all falcs are 14mb these days it seems so why not recycle - but not sure that these 4MB boards are going to be all that plentiful anymore after 25 years of being chucked in the bin.

Is there not some 4MB ramchip that will work in an ST circuit? Or even just one 4mb simm, seems easy enough to find on ebay especially laptop stuff.
You need to read everything which has been said... The next revision will have a new MMU with SRAM, so will be all SMT stuff. Of course there will be always some chip impossible to find in years to come.. Frankly, in 25 years time it can be someone else's problem.

This board is a Alpha, its proof the design can/will work, everything else is a bit irrelevant at this point anyway.
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Re: SUGGESTIONS

Post by KyleB » Tue Aug 28, 2018 12:48 pm

Fair enough... It's spread about through enough threads I'm never reading it in the right order

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