Saturday, January 16, 2016

Happy New Year


Hi folks, Happy New Year.

There's been quite a few developments with Prism in the past few months, though again a lot of them are "under the hood" and not particularly visual. A lot's been done to improve stability at higher CPU speeds, and there's also been a large amount of refactoring of Prism's microcode to make it easier to work on and add new features.

Over Christmas, I did a lot of compatibility testing (also known as just playing games), as well as some playing around with palettes...


Gauntlet II with a modified palette


Of course it wasn't ALL playing games and refactoring... I did do some work on adding new features, including Radstian mode (a 128x192 16 colour "chunky" mode with no colour clash). I also started adding César Hernández Bañó's additional screen modes (similar to Radstian mode but with different resolutions)

SpongeBob Radastanpants gazing lovingly at a ZX Uno prototype
Another Radastan mode demo pic (though personally I think Robot Chicken did it better)



I've also been working on a boot rom, based on a test ROM that César Hernández Bañó created. I'm re-learning Z80 after a break of several years, so César has been increadibly helpful, thanks mate! The boot ROM lets you chose which ROM you want to boot to, and lets you set a couple of options. It also displays the Prism logo which is based on a mock-up which Andrew Owen created for me a while ago. You can probably guess where I got the idea from ;)



Shine on, you crazy ROM selector.
The boot rom utilises Prism's 16 colour (4 plane) clashless mode and as you can see it also departs from the Spectrum's standard colours - for example non-bright yellow's orange.

13 comments:

  1. Hi,

    Sounds a really interesting project. Is there a webpage giving an overview of the project? I found a diagram of the memory model on Google Image search and went looking for more.

    An interesting video mode to try would be one using 4 1-bit planes combined for 256x192x16 colours.

    Looking forward to future updates.

    James

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    1. Hi James, when I get around to it, THIS will be the site with all the info on... I need to remove a load of outdated info and then write everything up properly! Prism's had a 4 plane 16 colour mode for over a year, and it's documented here... including some example screenshots ;) If you want to try Prism out, the Zesarux emulator emulates it now! :)

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    2. In fact the post you're commenting on has a couple of pictures of the 4 plane mode on it (the two pics of the prism boot screen are in this mode)

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    3. I've been working my way through the back posts, and it all sounds pretty exciting.

      One thing I'd like to see is a bit in the Video mode selection port to specify whether the Video memory is arranged in the clunky Spectrum way (default) or in a simple linear arrangement. I know the Spectrum arrangement has some advantages if you're working on an 8x8 graphics grid, but for anything off-grid it's a real pain. It would be nice to have both options.

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  2. How long will it take before this is an interface we plug into zx spectrums or buy as a new spectrum please?

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  3. have you seen the spectra on fruitcakes website yet?

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  4. and the ula+ website:
    https://sites.google.com/site/ulaplus/home

    http://www.fruitcake.plus.com/Sinclair/Spectrum/Spectra/SpectraInterface.htm

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  6. Roger: Of course I've seen the ULAplus website - Prism's done ULAplus for a couple of years now. There's example pictures on this blog.

    I've also seen spectra. It was released after I'd done a lot of work on Prism already so Prism won't include the Spectra modes.

    When will Prism be available as a computer to buy? I'm not likely to finish development for quite a while - it's not like I work on it fulltime, it's a project I'm doing in my spare time... It'll likely be months, if not over a year away. Once development has finished, I'll make the schematics, VHDL etc available for people to make their own (or even to make batches to sell) but I will not be mass producing them for sale myself.

    When will Prism be available as something that plugs into a spectrum? There's no plan for this to ever happen - a lot of Prism's functionality would not work in this format.

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  7. would it be possible to hook up one of the video processor chips that the msx2+ or truboR800 used please?

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    1. Not really. Prism's being modelled in FPGA and doesn't expose the CPU bus off-chip. You'd then need to mix the VPC output with Prism's own output.... Not something I want to do, sorry!

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  8. Has anyone tried to make a Spectrum clone using the eZ80, either using the physical chip or a FPGL implementation? It looks a really interesting chip. Compatible with Z80, but up to 4 times as fast at the same clock speed, and can be clocked to 50MHz. Imagine a Spectrum running at the equivalent of 200MHz? Also, it widens the register pairs to 24 bits, allowing 4MB of addressable memory. That would mean no need for paging, and high resolution graphics modes would be quite achievable.

    I'm sure there would be problems with such a chip. How do you make it match the timings of the Spectrum Z80, for example? Do you clock it back to 0.875MHz? Even then, I expect there would be lots of timing differences.

    Whether there would be interest in such a machine, I don't know, but it's fun to speculate.

    James

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