First coding attempts...
Pressing the '1' key is needed on turboR indeed. Same on real turboR. I don't have an MSX2 nearby to test on.
However, it doesn't always work when pressing the '1' key. It seems to depend on how long you press it. (Both on real GT and openMSX.)
Oh, I just tried: it's not pressing the '1' key... it's pressing any key. I got it to boot on a GT pressing the 's' key. 
(The boot sector is DOS1, so the turboR will boot already in Z80 mode with DOS1.)
And, the same thing also helps to get it booted on an MSX2 in openMSX. So, I guess something is wrong timing-wise in the program.
Hey, thanks Artrag for the nice feedback. Good to hear that you like it.
At this moment, I absolutely have no idea why it hangs. Could it be that the starting adress is #c000 ? I just took this one as it was in my code lines of 13 years ago. I haven't taken a look at memory locations/how msx memory works at all. The code is just 1.5kb compiled, thus I assume length isn't an issue.
In regard to how it was done? I guess we aren't in the 90s anymore where all things are a "secret", thus...
The checkered background is build up out of color 8 and 10. Scrolling this background is done by adding one colored line to the directon you want to go and removing one on the other side. The trick (or should I say, the smart idea) is that this is done by drawing a line and using a logical operator on it. Color 8 xor 2 = color 10, color 10 or 2 = color 8, color 8 or 2 = color 10, color 10 xor 2 = 8. In other words, the new line flips the color from 8 to 10 or from 10 to 8.
The original font has just one color, namely 7. But using the xor/or function on it, it also uses 5. But both are defined as the same. Color 7 xor 2 = color 5, color 5 xor 2 = color 7, color 7 or 2 = color 7, color 5 or 2 = color 7.
This technique provides that you can do anything on the background, without visibly affecting the foreground. But it also limits it to just these colors. I haven't taken a deeper look at it if it also works with different palet numbers.
I have to say, I haven't seen anyone use it before. I do know now that maggoo (iod metal limit, sonic player) did a checkered background scroll (32by32), but he had fixed vertical bars and used color splits to make it scroll.
I would still like to add a new 3rd (top) layer by using sprites, but that is something for the future
By BlueCrystal
Rookie (23)
15-01-2012, 23:19