Video mode switching

[sixxie]

I've written a little tool to help determine the effects of mid-scanline mode switching. It's called "stripe" and is available from http://www.6809.org.uk/tmp/da/tests/ as assembly source, .cas and .wav.

From the source:

Code: Select all

; Controls:
;     Up, Down, Left, Right - move stripe around by changing timings.
;     1, Q - Set/reset !A/G, GM2, GM1
;     2, W - Set/reset GM0 (and !INT/EXT)
;     3, E - Set/reset GM2, GM1 (switch between 32- and 16-byte graphic modes)
;     4, R - Set/reset CSS
;     Enter - Cycle through different screen patterns
;     Break - Return to BASIC

There's still stuff to figure out (in particular what determines which data and colours get used when a mode change happens mid-byte), but I've done some preliminary work in getting XRoar to do the right thing in the latest snapshot here: http://www.6809.org.uk/tmp/xroar/.

PAL CoCo timings are still generally out, but it does finally render the opening screen of the PAL DragonFire hack correctly!

[zephyr]

Thanks Ciaran!