DMA transfer in MODE4 (time in border area = fast memory) transfer one
byte per 8T
http://velesoft.speccy.cz/other/dma%203Trd+3Twr-mode4.png

DMA transfer in MODE4 (time in screen area = contended memory) transfer
one byte per 16T
http://velesoft.speccy.cz/other/dma%203Trd+3Twr-mode4-contended.png

11904 bytes per one frame 50Hz is maximum speed in mode 4 with active
screen. With external 1MB memory can be dma transfer faster. DMA scroll
can move screen data from external ram to internal ram. Access to
external ram is always fast(uncontended).

VELESOFT

Dne 9. 8. 2015 v 3:06 Simon Owen napsal(a):
Very interesting.  I didn't expect it to work well enough to be of use
on SAM, given how limited memory accesses are.  Does the CPU manage to
run at all while the DMA is active?

Is it possible to achieve the same result with an external board
replacing the internal CPU?  My soldering skills aren't up to replacing
the existing CPU with a socket!

Of course, your news might trigger you-know-who into action again...

Si

On 08/08/2015 23:46, VELESOFT wrote:
Here is my version of DATA-GEAR (Z80 DMA interface for SAM COUPE).
It's internal version for connection instead original Z80CPU (need
replace CPU with socket).

http://velesoft.speccy.cz/other/dma%203Trd+3Twr-long.png

VIDEO (sorry, bad quality and low FPS). Almost fullscreen scroll 25
fps on real sam coupe.
http://velesoft.speccy.cz/other/DMA_SAM_001.MPG



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