Palette and Vsync statements are in place now.
I had modest successes with freeware games PACMAN, DOODLE and SCRAM
(the last one displays a monochrome intro pic with too much space in between).
Text seems totally broken (right to left). Guess "hgdc_draw_text" must be implemented, first
Could someone have a look at the offsets in "vram_w" and "hgdc_display_pixels", please? https://dl.dropboxusercontent.com/u/37819653/BANNISTER/2016_09_19_RAINBOW_CPP.txt
Without schematics or intimate knowledge of the 7220, it seems too much trial & error (i do not even own the hardware).
Perhaps there a circuit diagram of the Rainbow-100 graphics option (part number should be 54-15688 or PC1XX-BA)...?