Scroll area routines.

Summary

Scroll area routines.
Macros
scroll_set	Initialize a scroll area.
Functions
scroll_hsync_callback	Set scroll coordinates with the current scroll display list entry, and program the next hsync callback.

Initialize a scroll area.

scroll_set id, top, bottom, x, y, flag

id	scroll area id (between 0 and 3).
top	coordinate of the first raster line.
bottom	coordinate of the last raster line.
x	X scroll coordinate.
y	Y scroll coordinate.
flag	VDC flags.

Set scroll coordinates with the current scroll display list entry, and program the next hsync callback.