mega-3dk v4.7

68000 3D engine base for Mega Drive, organized to grow from wireframe to flat-shaded triangles.

Focus of this v4.7

• Reduce obscure points in the bring-up
• Correct the misalignment between tile base and tile upload
• Bring up a default palette right in vdp_init
• Make the path framebuffer -> tiles -> name table -> VRAM more auditable

Important fixes in this version

• PRESENT_TILE_BASE stays 1 so tile 0 remains blank outside the centered 20x14 area

• vdp_init now calls vdp_init_default_palette

• Separate support for writing to CRAM has been added

• present_upload_minimal_cpu now documents and uses the tile base coherently

• STACK_TOP has been defined in config.inc, eliminating a boot loophole

Actual state

This v4.7 is still a serious technical bring-up, not a confirmed demo in the emulator. But the critical section is now shorter and has fewer obvious inconsistencies.

What's already more concrete

• Internal buffer 160x112 in 4bpp
• plot_pixel(x,y,color) in high/low nibble
• Entire Bresenham in draw_line
• Cube described by edges
• cube-first transformation
• Packing of the framebuffer in 8x8 tiles
• Linear name table 20x14
• Minimum upload to VRAM per CPU
• Default palette in CRAM at init

What's still missing to call it a ready demo

• Validate the first frame in the emulator
• Check the exact VDP command if a black screen or incorrect layout appears
• Actual reading of the 3-button controller
• Review the present for DMA after the first frame is validated

Next milestones

• v4.8: First visual frame validated
• v4.9: Backface culling + visible faces
• v5.0: Flat-shaded triangles