Cyberun: Routine at C33C

C33C: Save Restart Position

Used by the routine at RunFrame. Called when the bottom two bits of the frame counter are zero. The position of the ship is saved when it is safe to restart there: that is when the row of the screen at 57C1 holds only 55, or when none of the four tiles that are on the screen has anything in it other than the tile A6. The position is kept at F5FA to F5FF. This is a best reading of the code.
SaveRestartPosition	C33C	LD HL,$57C1	HL=57C1.
	C33F	LD B,$1C	B=1C.
SaveRestartPosition_Loop	C341	LD A,(HL)	Read HL.
	C342	CP $55	Jump to SaveRestartPosition_Tiles if A is not 55.
	C344	JR NZ,SaveRestartPosition_Tiles	Jump to SaveRestartPosition_Tiles if A is not 55.
	C346	INC L	Advance L.
	C347	DJNZ SaveRestartPosition_Loop	Decrease B and jump to SaveRestartPosition_Loop until none remain.
SaveRestartPosition_Zero	C349	LD B,$00	Clear B.
SaveRestartPosition_Store	C34B	LD HL,($CE57)	Fetch the word at MapPosition into HL.
	C34E	LD ($F5FA),HL	Update the map column of the position that the ship restarts at.
	C351	LD HL,($CE45)	Fetch the word at PositionAcross into HL.
	C354	LD A,L	A=L.
	C355	OR B	Set the bits of A that are set in B.
	C356	LD L,A	L=A.
	C357	LD ($F5FC),HL	Update the position of the ship: horizontal then vertical.
	C35A	LD HL,($CE41)	Fetch the word at HorizontalOffset into HL.
	C35D	LD ($F5FE),HL	Update the scroll offsets: horizontal then vertical.
	C360	RET	Return.
SaveRestartPosition_Tiles	C361	LD HL,$DC91	The visible tiles.
	C364	LD B,$04	B=04.
SaveRestartPosition_Row	C366	LD A,(HL)	Read HL.
	C367	AND A	Jump to SaveRestartPosition_Next if A is zero.
	C368	JR Z,SaveRestartPosition_Next	Jump to SaveRestartPosition_Next if A is zero.
	C36A	CP $A6	Return if A is not A6.
	C36C	RET NZ	Return if A is not A6.
SaveRestartPosition_Next	C36D	INC HL	Advance HL.
	C36E	DJNZ SaveRestartPosition_Row	Decrease B and jump to SaveRestartPosition_Row until none remain.
	C370	LD B,$01	B=01.
	C372	JR SaveRestartPosition_Store	Jump to SaveRestartPosition_Store.