Wednesday, July 16, 2014

Development moves to Cyclone IV

Back again after a bit of a break - apologies for the radio silence once again, but real life has a habit of getting in the way of things like blogs!

Much has happened with ZX Prism since my last post. The most major thing is that development moved from an Altera Cyclone II based dev board onto my shiny new Cyclone IV dev board. This has the major advantage that the Cylclone IV EP4CE15 FPGA used on this board has enough internal memory cells to implement the majority of the planned ZX Prism screen modes. Some of the more "out there" modes I had planned may fall by the wayside but there will still be plenty to choose from.

Since moving to the new dev board, progress has been swift. I got the basic video driver ported across in just a couple of hours and then set about building a Spectrum-like computer. In just under 2 days, I had ZX Prism initialising and displaying the hallowed "(c) 1982 Sinclair Research Ltd" message. In the top left of a 512x384 resolution screen :)  I tried alternative ROMS too, just to prove it wasn't a fluke and all worked happily - SE Basic and the ROM versions of JetPac and Pssst all booted fine.

Since then I've been battling getting a PS/2 keyboard working. It worked for about an hour and then stopped working entirely without me changing anything. Some poking and prodding about the dev board with a multimeter showed that the data signal wasn't making it to the FPGA anymore.  Routing the signal myself doesn't seem to have fixed things. I'll leave this for now - it's just led to several days of frustration and no further progress on Prism. I can come back to PS/2 later when I wire up the SD Card slots and replacement VGA connector. Yes, despite boasting a shiny new Cyclone IV, this dev board only has 1 bit VGA - that's right, at the moment ZX Prism only has 8 colours!

Anyway it's been ages since my last post so here's some pictures of ZX Prism showing off it's 4 different screen resolutions:

Standard 256x192 resolution, standard palette, standard attribute decoding
 512x192 resolution, standard palette, standard attribute decoding
(I will also add the monochrome Timex 512x192 mode later) 

 256x384 resolution, standard palette, standard attribute decoding

512x384 resolution, standard palette, standard attribute decoding

Booting the original Spectrum ROM in 512x384 resolution :)

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