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Re: ZX Spectrum Contended Memory - MultiColour Effects [Re: geecab] #113646
07/04/18 01:05 PM
07/04/18 01:05 PM
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R. Belmont Online content
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R. Belmont  Online Content
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This is the best technical description I've seen: https://faqwiki.zxnet.co.uk/wiki/Contended_memory

Re: ZX Spectrum Contended Memory - MultiColour Effects [Re: geecab] #113650
07/05/18 09:53 AM
07/05/18 09:53 AM
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geecab Offline OP
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Hi OG! Unfortunately, there isn't an all singing all dancing memory contention self test that I know of. It very much a "Run this Game/Demo/TestTool and check that the things you see on screen when running a real Spectrum are the same as when you are running a spectrum emulator" affair. Also, just having a perfect memory contention implementation does not mean all multi colour games & demos will look perfect. You need perfect ULA emulation too (So that the screen raster is perfectly sychronised with the Z80).

There are a number of ULA test tools that give an insight into the ULA timings of the Spectrum model that it is running on. I've ran all the tests I could find on my actual 48K and 128K+2 (I've posted links to galleries containing screenshots of my results), and have checked these results match perfectly with mame.
The tests can be found here:
http://wizard.ae.krakow.pl/~jb/qaop/tests.html

If you wanted a more enjoyable place to start, try loading the Nirvana+Engine demo on an 48k, 128K or +2A/+3. The tap can be found here:
https://spectrumcomputing.co.uk/index.php?cat=96&id=30002

If contended memory and ULA timings are correct, then the multi colour graphics will display correctly (I.e. When the demo runs you should see more than 2 colours occuyping an 8x8 pixel block, without any flicker or colour clash) regardless of what spectrum model you run it on.

Hope this helps smile

Re: ZX Spectrum Contended Memory - MultiColour Effects [Re: geecab] #113663
07/16/18 10:19 AM
07/16/18 10:19 AM
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geecab Offline OP
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I've managed to get my hands on a Spectrum +3 from an old friend of mine (Just had to re-solder a dry joint on the audio/tape socket and it seems to be able to load stuff now). Currently, the +2A/+3 ULA timing settings used for my mame implementation are based on the results that the Fuse emulator gives. Now I have an actual +3 I can double check if my +2A/+3 settings are correct. Soon I'll create another photo album containing screenshots of the +3 running floatspy, btime, stime, ulatest3 (Like I did for my Spectrum 48K and +2) smile

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