Chase H.Q.: Routine at A637

Otherwise A is negative.

A must be zero to arrive here.

I'm failing to understand what the following section does. It's a countdown that, when it hits zero, picks a new random countdown value summed with smash_5d1b. I can only think that it's a delay loop.

In-place decrementing counter.

When it hits zero we pick a random number...

This gets hit at some point during the smash process.

This smells like it's detecting position and turning that into lanes. The values are like those used by get_spawn_lanes.

Countdown+rng stuff again... as at A69B

In-place decrementing counter.

When it hits zero we pick a random number...

sampled IX = $A188 (hazards)

Distance to perp is 12 or less.

HL += (15 - A) * DE

This seems to be using the distance to the perp as a scale by which to adjust its horizontal position.

Distance to perp is 5 or less.

And then we do nothing with A?

This gets called whenever the perp is within sight of the hero car.
smash_handler	A637	LD A,($A230)	Return if perp_caught_phase > 0
	A63A	AND A
	A63B	RET NZ
	A63C	LD A,($A22E)	Call perp_sighted if sighted_flag is zero
	A63F	AND A
	A640	CALL Z,perp_sighted
	A643	LD A,(IX+$07)	A = IX[7]
	A646	AND A	Set flags
	A647	JR Z,sh_a650	Jump if zero
	A649	JP P,sh_a78a	Jump if positive
Otherwise A is negative.
	A64C	INC (IX+$07)	IX[7]++
	A64F	RET NZ	Return if non-zero
A must be zero to arrive here.
sh_a650	A650	PUSH IY	Preserve IY
	A652	LD C,(IX+$01)	C = IX[1]
	A655	LD B,$05	5 iterations
	A657	LD IY,$A19C	IY = &hazards[1]
	A65B	LD DE,$0014	DE = 20 -- stride of hazards
sh_hazards_loop	A65E	RLC (IY+$00)	If the hazard is active then jump to sh_a66c
	A662	JR C,sh_a66c	If the hazard is active then jump to sh_a66c
sh_a664	A664	ADD IY,DE	Move to next hazard
	A666	DJNZ sh_hazards_loop	Loop while B
	A668	POP IY	Restore IY
	A66A	JR sh_a68f	Jump to sh_a68f
sh_a66c	A66C	LD A,(IY+$0F)	A = IY[15]
	A66F	RLA	Check top bit
	A670	JP NC,sh_a664	Jump if clear
	A673	LD A,(IY+$01)	A = IY[1] - C
	A676	SUB C	A = IY[1] - C
	A677	JP NC,sh_a67e	Jump to sh_a67e if IY[1] > c
	A67A	ADD A,$02	A += 2
	A67C	JR sh_a680	Jump to sh_a680
sh_a67e	A67E	SUB $03	A -= 3
sh_a680	A680	JR NC,sh_a664
	A682	LD A,(IY+$11)	A = IY[17]
	A685	CP (IX+$12)	Compare to IX[18]
	A688	JP NZ,sh_a664
	A68B	POP IY	Restore IY $A650 pushed
	A68D	JR sh_a6d8	Jump to sh_a6d8
sh_a68f	A68F	LD A,$00	A = <self modified>
	A691	AND A	Jump if non-zero
	A692	JR NZ,sh_a6f6	Jump if non-zero
	A694	LD A,(IX+$01)	A = IX[1]
	A697	CP $07	Jump if A >= 7
	A699	JR NC,sh_a6f6	Jump if A >= 7
I'm failing to understand what the following section does. It's a countdown that, when it hits zero, picks a new random countdown value summed with smash_5d1b. I can only think that it's a delay loop. In-place decrementing counter.
	A69B	LD A,$14	A = <self modified> - 1 -- Self modified below
	A69D	DEC A	A = <self modified> - 1 -- Self modified below
	A69E	JR NZ,sh_update_counter	Jump to sh_update_counter if non-zero
When it hits zero we pick a random number...
	A6A0	INC C	[C incremented but overwritten in a moment - no effect?]
	A6A1	CALL rng	C = rng() & 31
	A6A4	AND $1F
	A6A6	LD C,A
This gets hit at some point during the smash process.
	A6A7	LD A,($5D1B)	A = smash_5d1b + C
	A6AA	ADD A,C	A = smash_5d1b + C
sh_update_counter	A6AB	LD ($A69C),A	Self modify 'LD A,x' at A69B (above) to load A
This smells like it's detecting position and turning that into lanes. The values are like those used by get_spawn_lanes.
	A6AE	LD HL,($A26C)	HL = road_pos - 164
	A6B1	LD DE,$00A4
	A6B4	SBC HL,DE
	A6B6	LD BC,$0404	BC = $0404
	A6B9	JR C,sh_a6cf	Jump to sh_a6cf if HL < 164
	A6BB	LD E,$46	DE = $0046
	A6BD	DEC B	BC = $0304
	A6BE	SBC HL,DE	HL -= DE -- includes previous
	A6C0	JR C,sh_a6cf	Jump to sh_a6cf if HL < 70
	A6C2	DEC B	BC = $0203
	A6C3	DEC C	BC = $0203
	A6C4	SBC HL,DE	HL -= DE -- includes previous
	A6C6	JR C,sh_a6cf	Jump to sh_a6cf if HL < 70
	A6C8	DEC B	BC = $0102
	A6C9	DEC C	BC = $0102
	A6CA	SBC HL,DE	HL -= DE -- includes previous
	A6CC	JR C,sh_a6cf	Jump to sh_a6cf if HL < 70
	A6CE	DEC C	BC = $0101
sh_a6cf	A6CF	LD A,(IX+$12)	A = IX[18]
	A6D2	CP C	Jump to sh_a6d8 if A == C
	A6D3	JR Z,sh_a6d8	Jump to sh_a6d8 if A == C
	A6D5	CP B	Jump to sh_a6f6 if A == B
	A6D6	JR NZ,sh_a6f6	Jump to sh_a6f6 if A == B
sh_a6d8	A6D8	LD C,(IX+$12)	C = IX[18]
	A6DB	CALL rng	Call rng
	A6DE	INC C	C++
	A6DF	AND A	Jump if C positive
	A6E0	JP P,sh_a6e5	Jump if C positive
	A6E3	DEC C	C -= 2
	A6E4	DEC C	C -= 2
sh_a6e5	A6E5	LD A,C	A = C
	A6E6	AND A	Set flags
	A6E7	LD C,$02	C = 2
	A6E9	JP Z,sh_a6f2	Jump if A is zero
	A6EC	CP $05	Jump if A < 5
	A6EE	JR C,sh_a6f3	Jump if A < 5
	A6F0	LD C,$FE	C = $FE
sh_a6f2	A6F2	ADD A,C	A += C
sh_a6f3	A6F3	LD (IX+$12),A	IX[18] = A
sh_a6f6	A6F6	LD C,(IX+$01)	C = IX[1]
	A6F9	CALL get_spawn_lanes	Call get_spawn_lanes
	A6FC	LD A,(IX+$12)	A = IX[18]
	A6FF	CP B	Jump to sh_a707 if A >= B -- upper boundary?
	A700	JR NC,sh_a707	Jump to sh_a707 if A >= B -- upper boundary?
	A702	ADD A,$02	A += 2
	A704	LD (IX+$12),A	IX[18] = A
sh_a707	A707	CP C	Jump to sh_a711 if A <= C -- lower boundary?
	A708	JR Z,sh_a711
	A70A	JR C,sh_a711
	A70C	SUB $02	A -= 2
	A70E	LD (IX+$12),A	IX[18] = A
sh_a711	A711	LD A,(IX+$12)	A = IX[18]
	A714	LD HL,$A7E6	HL = $A7E6 -> table_a7e7 data block
	A717	ADD A,L	L += A
	A718	LD L,A	L += A
	A719	LD A,(IX+$05)	A = IX[5]
	A71C	CP (HL)	A == *HL ?
	A71D	LD C,$01	C = 1
	A71F	JR Z,sh_a735	Jump if A == *HL
	A721	JR C,sh_a72e	Jump if A < *HL
	A723	SUB $0A	A -= 10
	A725	JR C,sh_a72a	Jump if A was < 10
	A727	CP (HL)	A == *HL ?
	A728	JR NC,sh_a737	Jump if A >= *HL
sh_a72a	A72A	DEC C	C--
	A72B	LD A,(HL)	A = *HL
	A72C	JR sh_a737	Jump sh_a737
sh_a72e	A72E	ADD A,$0A	A += 10
	A730	JR C,sh_a735	Jump if A+10 carried
	A732	CP (HL)	A == *HL ?
	A733	JR C,sh_a737	Jump if A < *HL
sh_a735	A735	DEC C	C--
	A736	LD A,(HL)	A = *HL
sh_a737	A737	LD (IX+$05),A	IX[5] = A
	A73A	LD A,C	Self modify 'LD A' @ sh_a68f to load C
	A73B	LD ($A690),A	Self modify 'LD A' @ sh_a68f to load C
	A73E	LD A,$00	A = <self modified>
	A740	AND A	Set flags
	A741	LD DE,$001E	DE = $1E
	A744	LD HL,$00E6	HL = $E6
	A747	JR NZ,sh_a762	Jump sh_a762 if non-zero
Countdown+rng stuff again... as at A69B In-place decrementing counter.
	A749	LD A,$14	A = <self modified> - 1 -- Self modified below
	A74B	DEC A	A = <self modified> - 1 -- Self modified below
	A74C	LD ($A74A),A	Self modify 'LD A,x' @ A749 (above) to load A
	A74F	JR NZ,sh_a776	Jump to sh_a776 if non-zero
When it hits zero we pick a random number...
	A751	PUSH HL	Preserve HL [what's in it?]
	A752	CALL rng	Call rng
	A755	POP HL	Restore HL
	A756	AND $0F	C = (result of rng) & 15
	A758	LD C,A	C = (result of rng) & 15
	A759	LD A,($5D1C)	A = smash_5d1c + C
	A75C	ADD A,C	A = smash_5d1c + C
	A75D	LD ($A74A),A	Self modify 'LD A,x' @ A749 (above) to load A
	A760	LD A,$0A	A = 10
sh_a762	A762	DEC A	A--
	A763	LD ($A73F),A	Self modify 'LD A,x' @ A73E (above) to load A
	A766	JR Z,sh_a776	Jump to sh_a776 if zero
sampled IX = $A188 (hazards)
	A768	LD A,(IX+$01)	A = IX[1] -- load hazard_1 distance byte
	A76B	CP $0D	Jump if A >= 13 -- too far
	A76D	JR NC,sh_a776	Jump if A >= 13 -- too far
Distance to perp is 12 or less. HL += (15 - A) * DE This seems to be using the distance to the perp as a scale by which to adjust its horizontal position.
	A76F	CPL	B = (15 - A) -- iterations
	A770	ADD A,$0E
	A772	LD B,A
sh_a773_loop	A773	ADD HL,DE	HL += DE
	A774	DJNZ sh_a773_loop	Loop to loop_a773 while B > 0
sh_a776	A776	LD A,(IX+$01)	A = IX[1] - 6 -- load hazard_1 distance byte again
	A779	SUB $06	A = IX[1] - 6 -- load hazard_1 distance byte again
	A77B	JR NC,sh_store_exit	Jump to sh_store_exit if A >= 6
Distance to perp is 5 or less.
	A77D	ADD A,$05	Put back most of what we just subtracted
	A77F	ADD A,A	Multiply by 8
	A780	ADD A,A
	A781	ADD A,A
And then we do nothing with A?
	A782	ADD HL,DE	HL += DE
sh_store_exit	A783	LD (IX+$0D),L	wordat(IX + 13) = HL -- store horizontal position (or accel?)
	A786	LD (IX+$0E),H
	A789	RET	Return
sh_a78a	A78A	LD (IX+$07),$FC	IX[7] = $FC
	A78E	CP $03	Jump if A < 3 -- preserve A
	A790	PUSH AF
	A791	JR C,sh_check_boost
	A793	SUB $03	A -= 3 -- 0..
sh_check_boost	A795	EX AF,AF'	Bank
	A796	LD A,($A24E)	Load turbo boost time remaining (60..0)
	A799	AND A	Set flags
	A79A	LD A,$C8	200 when not turbo boosting
	A79C	JR Z,sh_a7a0	Jump if no turbo boost
	A79E	LD A,$E6	230 when turbo boosting
sh_a7a0	A7A0	EX AF,AF'	Bank value chosen from boost; Unbank other
	A7A1	CALL cc_hit_scenery2	Call cc_hit_scenery2
	A7A4	LD HL,($B32F)	Read HL from 'LD BC,x' @ B32E
	A7A7	LD DE,$0028	HL += 40
	A7AA	ADD HL,DE	HL += 40
	A7AB	LD ($B32F),HL	Self modify 'LD BC,x' @ B32E
	A7AE	LD D,$00	D = 0 -- bonus middle digit
	A7B0	POP AF	-- restore A which holds the IX[7] flags from earlier AND FLAGS TOO
	A7B1	LD HL,$B4F0	Put a call to smash on the stack
	A7B4	PUSH HL	Put a call to smash on the stack
	A7B5	JR NC,sh_a7be	Jump if no carry
	A7B7	CP $02	Jump if A == 2
	A7B9	JR Z,sh_a7be	Jump if A == 2
	A7BB	PUSH HL	Put another call to smash on the stack
Break?
	A7BC	LD D,$04	D = 4 -- bonus middle digit
sh_a7be	A7BE	LD A,($8007)	D = wanted_stage_number + D (D could be 0 or 4)
	A7C1	ADD A,D
	A7C2	LD D,A
	A7C3	LD E,$00	E = 0 -- bonus top digit(s)
	A7C5	LD A,($8006)	Jump if retry_count is zero
	A7C8	AND A
	A7C9	JR Z,sh_retry_was_zero
	A7CB	LD A,D	Middle digit(s) of bonus
	A7CC	LD D,E	Set top two digits of bonus
	A7CD	RLCA	Move middle digit into position
	A7CE	RLCA
	A7CF	RLCA
	A7D0	RLCA
	A7D1	LD E,A	Set middle digits of bonus
sh_retry_was_zero	A7D2	XOR A	Clear low digits of bonus
	A7D3	CALL bonus	Call bonus
	A7D6	LD A,$05	A = 5
	A7D8	LD ($A73F),A	Self modify 'LD A' @ A73E to load A
	A7DB	LD HL,$98D6	Point HL at smash_chatter ("BEAR DOWN" / "OH MAN" / etc.)
	A7DE	CALL start_chatter	Call start_chatter (priority 5)
	A7E1	LD BC,$0301	Effect 3 (car crash), Priority 1
	A7E4	JP start_sfx	Exit via start_sfx