Using copper to get interlace is involved, consult Hardware Reference Manual.
Using Blitz 2 to open an Intuition screen in interlace is pretty easy as per page 173;-
https://ia801009.us.archive.org/33/items/bb21manual/BB21Manual.pdfEDIT: The problem with interlace is that the start address of each bitplane has to be changed after each raster frame.
On a non-interlaced screen, the data read position is just reset back to the start address at the end of each frame.
This is no good for interlace, first the even frame is displayed, and the next video frame, the odd lines are displayed.
This makes for a convoluted copper list, having to change the bitplane start position on each frame.
Hey, you wanted total control in assembler. You got it.
