Thanks, Crazyc! I made some progress. Debugging is dead slow, plus i havent mastered palette and IRQ handling yet.
How do i set up a second, independent palette for SCREEN 2?
Is there a way to speed up debugging under Visual Studio 2015 (i have quite a beefy laptop with a core I7 and an SSD, but it comes to a crawl with debug builds)...?
I added a macro statement for VSYNC
MCFG_UPD7220_VSYNC_CALLBACK(DEVWRITELINE("upd7220", upd7220_device, ext_sync_w)))
... but don't know where to put the actual IRQ code:
if(m_GDC_MODE_REGISTER & GDC_MODE_ENABLE_VSYNC_IRQ)
(WIP: pacman ghosts on the right. No palette, no colors. Still some VRAM bugs)