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How to write an Amstrad CPC emulator (irespa.eu)
41 points by ingve on May 31, 2020 | hide | past | favorite | 5 comments



This is pretty old - mid-90s, I think.

Since then the state of the art in CPC emulators has moved on a lot. Most of the advances have been in emulating the quirks of the CRTC (Cathode Ray Tube Controller). Most games didn't make much use of the CRTC beyond the basics, but demomakers have been pushing its bounds for 30 years now. Here's a fairly typical recent example of a CPC demo: https://www.youtube.com/watch?v=6wBwbRYL-F4&feature=youtu.be

Even back in the mid-90s we were stretching the CRTC to such an extent that differences were apparent depending whether Amstrad had bought a batch of chips from Hitachi, Motorola or NEC. It's worth browsing Pouet to see what's been done in the years since.


That demo is impressive. I have an old Kaypro, and it uses the same 6845 CRTC. I would not have guessed you could push it like that.


I do remember fiddling with the CRTC back in the day. There used to be a trick where you could change the color palette (16 colours iirc) on the horizontal retrace to get extra colours, and I think some later games took advantage of this.


Demo sceners have also figured out how to reprogram the scanning position in memory for each scanline, with impressive results:

https://floooh.github.io/tiny8bit/cpc.html?file=cpc/dtc_cpc....

https://floooh.github.io/tiny8bit/cpc.html?file=cpc/logons_r...


That is wonderful, takes me back :-). You can even see a bit of jitter in the lines of colours since the interrupt wasn't precise enough to really do this.




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