frame buffer problem causes horizontal line problems at specific y positions

[mattvenn]

Expected behaviour

drawing a horizontal line by setting pixels in the frame buffer should result in a single pixel wide line on the display.

Resulting behaviour

• Drawing a line at y = 2 works as expected
• Drawing a line at y = 3 results in 2 short lines with a pixel space between them
• Drawing a line at y = 4 results in 2 px wide line in some places
• Drawing a line at y = 5 works as expected

To reproduce

• Clone https://github.com/mattvenn/had-badge-draw-app/tree/linetest
• make and copy to badge
• button up draws a 200 pix horizontal line at y = 2
• button right draws at y = 3 (with glitches as described above)
• button down draws at y = 4 (with glitches as above)
• button left draws at y = 5 which works as expected

[shaos]

Based on my experience it looks like DMA draws every ODD line of framebuffer twice (and EVEN lines are completely ignored). This is happening with FB only - tiles and sprites look high-res...

[shaos]

It sounds funny, but I think I've just fixed EVEN lines issue :)

Example with lines from Matt now draw "ghost" short line in case of y=4, but in all other cases lines look correct (I made background blue to count pixels):

[shaos]

This is my pull-request: https://github.com/Spritetm/hadbadge2019_fpgasoc/pull/155

[Spritetm]

Seems fixed by Shaos' PR.