BG fetch Force Blank test rom

[paulb-nl]

This is a test rom for showing the background fetching behavior during Force blank.

Press up or down to move the IRQ vertically and L & R to move it horizontally.

BG1-3 at the top half of the screen are all enabled with different priority. At the bottom half, only one BG is enabled.

The green color after disabling Force blank is palette color $1F because it reads Tile map data $FFFF for BG 3 with pixel data $FF. The color changes to dark purple at the lower BG1 because BG3 is disabled so it shows color $7F. The small tiles sometimes visible next to the colors are tile $3FF of BG1&2.

bg_fb.smc.zip

With PR #429 this behavior is exactly the same as original hardware.

Here is a video of original hardware:

2025-09-27.17-30-56_bg_fb_console.mp4