Really crazy idea ...

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Petari
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Re: Really crazy idea ...

Post by Petari » Sat Aug 11, 2018 8:48 am

Cyprian wrote:
Fri Aug 10, 2018 10:07 pm
IIRC minimal data block in ST DMA is 16 bytes.
Well, that's true in some way, but to achieve it, you need to reset FIFO after every 16 byte block, and that needs some instructions + ergo, it will be slow.
Then, you can not split just like that all screen writes to 16 byte blocks - and all code for screen write would need it - that's just not usable way.
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Re: Really crazy idea ...

Post by Petari » Sat Aug 11, 2018 9:09 am

SolderGirl wrote:
Fri Aug 10, 2018 10:56 pm
...
If that is correct, it would be perfect.
Because PCIe works with a packet protocol, with packets of 4 x 32bit words each. So That is exactly 16 bytes packets. That would fit nicely.
PS:
"The frame format for PCIe is shown in the graphic below. The frame is made up of a 1-byte Start-of-Frame, 2-byte Sequence Number, 16 or 20-byte Header, 0 to 4096-byte Data field, 0 to 4-byte ECRC field, 4-byte LCRC, and 1-byte End-of Frame. The smaller the number of bits transferred in the data field the greater the over-head becomes. A zero byte data field results in a 100 percent over-head, because no data was transferred."

From this, it looks like a typical Frame would be something like 28 bytes + Data, but i don't know the data formats used.
Also i don't know how flexible the block sizes for the DMA port are
You want to use protocol what is used on min. 1000x faster computers. How looks drawing of 1 letter to screen ?
Here is example in 1 bit plane: write 1 byte, incr. dest address by 80 (640px width) , write next byte ... repeat it 14 time yet (for 16 px height).

With PCI protocol: need to write address in header, I guess, then 1 byte data, then ECRC, LCRC - ah, who will calculate it ? You need extra chips for that, because 8 MHz 68000 will take ages for that. Repeat all it 16 times totally. Even without ECRC it will be at least 10x slower that straight write to video RAM. With more bitplanes it can be little better, still much slower than staright write.

When it can be good ? Indeed in case of transferring larger data block at once. So, let's say drawing some nice photo on screen. Then can use DMA with it's 512 byte blocks well. Even calculating those CRCs with 68000, maybe - depends on speed with 68K and availability of CRC chips.

Desktop and usual VDI, GEM graphic will be just too slow.

I say that this hybrid - of old architecture with latest graphic cards, which btw. have at least 100x more RAM than whole Atari ST is just not good idea.
There are already working solutions with ISA and PCI cards. Basically all solutions with USB on Ataris are slow. This will be case with PCIe too . Just much worse.
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Re: Really crazy idea ...

Post by arf » Sat Aug 11, 2018 12:46 pm

SolderGirl wrote:
Fri Aug 10, 2018 5:26 pm
So maybe, just maybe, it would be possible to somehow connect a PCIe Graphics Card to the Atari, maybe over the DMA-Port?
The serial ports of the ST only do 19200bps, that would be too slow for use, but the DMA-Port can do well over 1 MB/s,
that might be enough to run a framebuffer at relatively low resolution.
Sure you could do. There have been solutions like that for the 68k Macintosh: graphics cards via SCSI. And ACSI’s no worse than the SCSI ports of the 68k Macs back then. It has been reasonably fast.
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Re: Really crazy idea ...

Post by Petari » Sat Aug 11, 2018 2:59 pm

68K MACs were for sure not with PCIe cards.
DMA port could work with some 8-bit PCIe gfx card. of course with some interface.
I'm not saying that it is not possible. Just don't think that is good solution. Some older PCI or ISA card is what suits ST, 680xx CPUs better.
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Re: Really crazy idea ...

Post by troed » Sat Aug 11, 2018 4:01 pm

With the reSTFM (sorry exxos, don't recall your name for it) we should be able to do both the doubleST* video modes (640x200x16, 1280x200x4, 1280x200x2) but also thanks to czietz' amazing sw-solution discovery also 320x400x16 and 640x400x4.

And if we include Smonson's Shifter-FPGA one more very attractive one that I'll let him talk about :)

regards,
Troed

*) Needs 16MHz CPU, faster RAM and ROM and overclocks MMU and Shifter.

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Re: Really crazy idea ...

Post by exxos » Sat Aug 11, 2018 5:54 pm

Speculate shifter resolutions based on 50mhz bandwidth ;)
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

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Re: Really crazy idea ...

Post by troed » Sat Aug 11, 2018 6:04 pm

exxos wrote:
Sat Aug 11, 2018 5:54 pm
Speculate shifter resolutions based on 50mhz bandwidth ;)
Yeah I wasn't sure whether to plan for FPGA-MMU as well :)

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Re: Really crazy idea ...

Post by exxos » Sat Aug 11, 2018 6:17 pm

troed wrote:
Sat Aug 11, 2018 6:04 pm
Yeah I wasn't sure whether to plan for FPGA-MMU as well :)
Need to finish the booster work then its porting suska cores... Shouldn't take much doing... We just need to convince someone to add more resolution registers ;). No reason not to add chunky either.. Also could add more bit functions into the blitter for effects... 50mhz blitter also BTW ;)
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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