msx-karts 1st playable demo

Nice nice!
Have you considered using outd to mirror stuff in stead of using a rotated/mirrored copy?

You got me thinking for a while! But I think I do not get any useful mirroring options:

The original code was:

pop de
add hl, de
ld a, (hl)
out (0x98), a

but did find out that outi makes it 2 cycles faster. The increment is actually a side-effect that I need to compensate on the lockup table.

To perform some mirroring I would need to replace the add hl, de for a "sub hl, de", but this instruction does not exist :S

pop de
add hl, de
ld a, (hl)
out (0x98), a

In the texture map routine I made for my 3D engine I did the same. However my strategy was to have DE as a fixed coordinate in the map and then do a POP HL as an offset-value. This way I had an (easier to calculate) offset table and I could move DE around as origin in the texture. Due to the fact that you could POP HL all the time you can simply ignore the side effect of the OUTI.

salutte would it help you an arrangement of the characters in columns, instead of rows, in order to be able to work on adjacent VRAM addresses ?

Wow! This is very impressive! Looks amazing, a little like F-nano 2 for MSX turbo-R, but then even better.
On a msx1... I'm speechless