Since the only time I have to spend on my JetPack project is over the winter months, I do get a lot of time to think about the final design, which will commence when I am once again buried under a layer of snow.
I have 2 hours of commute time per day to work, so I have been evolving things towards the final design.
All of the prototyping posted here over the last few years has been "smoke testing" of various ideas.
There actually was smoke once, when I plugged an SRAM chip in reverse!
Anyhow, I am getting very close to the final design, which now celebrates all of the functionality of the 6560 rather than hiding it.
The final JetPack design is basically a continuation of the old Super Expander, with a crazy advanced MMU inside.
One feature I decided to add this morning is a tiny Cartridge Port.
Since JetPack itself is a standard sized VIC cartridge, the new top mounted Mini Cart Port will be only a fraction of the size.
The thinking here is that Jetpack plugs in, gives the user access to the advance MMU and scripting engine, and all game / demo code can be loaded or saved to mini cartridges. This allows JetPack to stay connected at all times.
I am not interested in cross emulation or talking to the modern PC world, so SD / FAT is of no interest to me.
What I did find is a nice 16 Megabyte SPI flash for a few bucks...
https://www.digikey.ca/product-detail/e ... ND/7100880
This will make a nice "Micro Cartridge" that will plug into the tiny slot I plan to put in the top of the JetPack cartridge.
16MB should be enough to make a nice size VIC game, including code and graphics.
The SPI may even be quick enough to not require the giant SRAM media buffer.
I will have to test one soon.
I am also working out the most robust video format to use.
So far it looks like 184 x 176 with char and aux color updates on every scan line.
Since my frames are raster synced at 30FPs for zero flicker and shear, there are some limitations.
I also can't stand the look of per scanline frame changing borders, so that is out.
Audio, keyboard, and joystick are also updated per frame, so cycles are not unlimited.
Looks like the JetPack Engine will do...
- 184(92) x 176 with 4 colors + 2 changeable per line, and all changeable per frame.
- 30 Frames per second, raster synced for zero shear and flicker.
- All 4 voices and volume updated several times per frame.
JetPack will be able to lay down a 184 x 176 screen (from a much larger playfield) and then many alpha aware sprites at 30 frames per second, allowing for massive scrolling games with single pixel scrolling capability. A game like Turrican comes to mind.
The cool part will be that all graphics and sound are generated only by the 6560 in the unmodified stock VIC-20.
The real power inside JetPack will be the raster synced MMU, which will shuttle graphics bytes from a larger SPI memory to the VIC in such a way as to eliminate all flicker and offer 30 frames per second multilayered game screens.
Still a lot of beta testing to be done.
Odd... normally "Feature Creep" adds extra, but in my JetPack project, I have gone from HD VGA + stereo sound all the way down to nothing but native VIC-20 sound and graphics.
Until the next rainy (or snowy) day.... Later!
Radical Brad