Chase H.Q.: Routine at A955

A955: Chooses random dirt and stones (not tumbleweeds though)

One particle is set up per frame on dirt track sections, and nothing happens unless both on_dirt_track and allow_spawning are non-zero. The sign of a random byte picks the type, 1 for a stone and 2 for dirt, and a second random byte gives the horizontal position. Both go into the particle table at $ED28 and the three self modified flags that drive the laying out and drawing of the particles are set to 1. Used by the routines at main_loop and drive_attract_demo.
choose_dirt_and_stones	A955	LD A,($A248)	Return if on_dirt_track is zero
	A958	AND A
	A959	RET Z
	A95A	LD A,($A254)	Return if allow_spawning is zero
	A95D	AND A
	A95E	RET Z
	A95F	LD DE,$ED28	Point DE at (something above the stack)
	A962	CALL rng	Generate a random byte
	A965	AND A	Store 1 (stone) if it's +ve or zero, or 2 (dirt) if it's -ve
	A966	LD A,$01
	A968	JP P,cdas_store
	A96B	INC A
cdas_store	A96C	LD (DE),A
	A96D	CALL rng	Generate a random byte -- the entry's position byte; see layout_dirt_and_stones
	A970	INC DE	Store that random byte
	A971	LD (DE),A	Store that random byte
	A972	LD A,$01	Self modify 'LD A' @ layout_dirt_and_stones to load 1
	A974	LD ($A97F),A
	A977	LD ($C0BC),A	Self modify 'LD A' @ rm_hazard_continue to load 1
	A97A	LD ($A9DF),A	Self modify 'LD A' @ draw_dirt_and_stones to load 1
	A97D	RET	Return