Chase H.Q.: Routine at 5B00

5B00: The game has loaded

This is entered when the game is first loaded. It disables interrupts, moves memory into the right position, detects 128K machines and then runs the secondary loader to load the first stage (48K) or all stages (128K) as required.
The game starts here.
start	5B00	DI	Disable interrupts
	5B01	LD SP,$5C00	Set stack pointer
Copy $4910 bytes from $5C00+ to $76F0+ (copying backwards to avoid overlap).
	5B04	LD HL,$A50F	Final source byte
	5B07	LD DE,$BFFF	Final destination byte
	5B0A	LD BC,$4910	Count
	5B0D	LDDR	Copy
Detect 128K machines. Assuming bank 0 is mapped in to start with, we copy a byte from bank 0.
detect_128k	5B0F	LD HL,$FFF0	Read the byte at $FFF0 into E
	5B12	LD E,(HL)	Read the byte at $FFF0 into E
Now we modify it, then store it back after attempting to page in bank 1.
	5B13	LD A,$01	Attempt to map RAM bank 1 to $C000
	5B15	LD BC,$7FFD
	5B18	OUT (C),A
	5B1A	LD A,E	Increment the read byte by $FD (a convenient non-zero value)
	5B1B	ADD A,C
	5B1C	LD (HL),A	Store it
If the modified byte remains present after restoring bank 0 then it's a 48K machine.
	5B1D	XOR A	Attempt to map RAM bank 0 to $C000
	5B1E	OUT (C),A	Attempt to map RAM bank 0 to $C000
	5B20	LD A,(HL)	Load potentially changed byte
	5B21	LD (HL),E	Restore original byte
	5B22	LD HL,$5B7D	Point HL at loader_commands_48K
If byte was modified no paging took place, so this is a 48K machine.
	5B25	CP E	If modified, jump to loader with loader_commands_48K setup
	5B26	JR NZ,loader	If modified, jump to loader with loader_commands_48K setup
mode_is_128k	5B28	LD HL,$5B87	Otherwise point HL at loader_commands_128K
The loader accepts a command list and uses it to load the game into memory. The 48K command list at loader_commands_48K loads stage 1, then starts the game. The 128K command list at loader_commands_128K loads all stages while paging in the appropriate banks, then starts the game.
loader	5B2B	LD E,(HL)	Load a handler address from HL
	5B2C	INC HL
	5B2D	LD D,(HL)
	5B2E	INC HL
	5B2F	PUSH DE	Call the handler
	5B30	RET	Call the handler
Loader handler that loads a stage.
loader_load	5B31	PUSH HL	Preserve command list address
	5B32	LD IX,$5BD5	Address of loader_scratch
	5B36	LD DE,$0002	Length of loader_scratch
	5B39	CALL loader_load_chunk	Call loader_load_chunk
	5B3C	POP HL	Restore command list address
loader_load_headerless	5B3D	LD E,(HL)	Load address from command list into IX
	5B3E	INC HL
	5B3F	LD D,(HL)
	5B40	INC HL
	5B41	PUSH DE
	5B42	POP IX
	5B44	LD E,(HL)	Load length from command list into DE
	5B45	INC HL
	5B46	LD D,(HL)
	5B47	INC HL
	5B48	PUSH HL	Preserve command list address
	5B49	CALL loader_load_chunk	Call loader_load_chunk
The following instruction is the point at which this disassembly was captured.
	5B4C	POP HL	Restore command list address
	5B4D	JR loader	Process next entry
Subroutine that loads DE bytes to address IX.
loader_load_chunk	5B4F	CALL tape_load_at_ix	Call tape_load_at_ix
	5B52	RET C	Return if no errors
Infinitely cycle through border colours if a tape loading error occurred.
loader_load_failed	5B53	OUT ($FE),A
	5B55	INC A
	5B56	JR loader_load_failed
Loader handler that pages in the specified RAM bank.
loader_set_bank	5B58	LD A,$80	Page in RAM where interrupt vector lives
	5B5A	LD I,A	Set Interrupt Control Vector Register
	5B5C	LD A,(HL)	Load 128K paging flags byte
	5B5D	INC HL	Second byte is unused
	5B5E	INC HL	Second byte is unused
	5B5F	LD BC,$7FFD	128K: Set paging register
	5B62	OUT (C),A	128K: Set paging register
	5B64	JR loader	Process next entry
Loader handler that copies data around.
loader_copy	5B66	PUSH HL	Preserve command list address
	5B67	LD HL,$5C00	Move $5C00..$76EF to $C000 onwards
	5B6A	LD DE,$C000
	5B6D	LD BC,$1AF0
	5B70	LDIR
	5B72	POP HL	Restore command list address
	5B73	JR loader	Process next entry
Loader handler that starts the game.
loader_start_game	5B75	LD A,(HL)	Load entrypoint address from HL
	5B76	INC HL
	5B77	LD H,(HL)
	5B78	LD L,A
	5B79	XOR A	Set border to black
	5B7A	OUT ($FE),A	Set border to black
	5B7C	JP (HL)	Exit via entrypoint just read
Loader commands for 48K mode.
loader_commands_48K	5B7D	DEFW loader_load	Load stage 1 at $5C00 ($1AF0 bytes)
	5B7F	DEFW bitmap_horizon,$1AF0	Load stage 1 at $5C00 ($1AF0 bytes)
	5B83	DEFW loader_start_game	Start game at entrypt_48k
	5B85	DEFW entrypt_48k	Start game at entrypt_48k
Loader commands for 128K mode.
loader_commands_128K	5B87	DEFW loader_load	Load stage 1 at $5C00 ($1AF0 bytes)
	5B89	DEFW bitmap_horizon,$1AF0	Load stage 1 at $5C00 ($1AF0 bytes)
	5B8D	DEFW loader_set_bank	Set bank 1 (second byte is unused in Set Bank commands)
	5B8F	DEFB $01,$00	Set bank 1 (second byte is unused in Set Bank commands)
	5B91	DEFW loader_copy	Copy $5C00..$76EF to $C000
	5B93	DEFW loader_load	Load stage 2 at $E000 ($1AF0 bytes)
	5B95	DEFW $E000,$1AF0	Load stage 2 at $E000 ($1AF0 bytes)
	5B99	DEFW loader_set_bank	Set bank 6
	5B9B	DEFB $06,$00	Set bank 6
	5B9D	DEFW loader_load	Load stage 3 at $C000 ($1AF0 bytes)
	5B9F	DEFW $C000,$1AF0	Load stage 3 at $C000 ($1AF0 bytes)
	5BA3	DEFW loader_load	Load stage 4 at $E000 ($1AF0 bytes)
	5BA5	DEFW $E000,$1AF0	Load stage 4 at $E000 ($1AF0 bytes)
	5BA9	DEFW loader_set_bank	Set bank 7
	5BAB	DEFB $07,$00	Set bank 7
	5BAD	DEFW loader_load	Load stage 5 at $C000 ($1AF0 bytes)
	5BAF	DEFW $C000,$1AF0	Load stage 5 at $C000 ($1AF0 bytes)
	5BB3	DEFW loader_load	Load end screen at $E000 ($1AF0 bytes)
	5BB5	DEFW $E000,$1AF0	Load end screen at $E000 ($1AF0 bytes)
	5BB9	DEFW loader_set_bank	Set bank 3
	5BBB	DEFB $03,$00	Set bank 3
	5BBD	DEFW loader_load_headerless	(Headerless) Load animated title screen at $C000 ($4000 bytes)
	5BBF	DEFW $C000,$4000
	5BC3	DEFW loader_set_bank	Set bank 4
	5BC5	DEFB $04,$00	Set bank 4
	5BC7	DEFW loader_load_headerless	(Headerless) Load sampled speech at $C000 ($4000 bytes)
	5BC9	DEFW $C000,$4000	(Headerless) Load sampled speech at $C000 ($4000 bytes)
	5BCD	DEFW loader_set_bank	Set bank 0
	5BCF	DEFB $00,$00	Set bank 0
	5BD1	DEFW loader_start_game	Start game at entrypt_128k
	5BD3	DEFW entrypt_128k	Start game at entrypt_128k
loader_scratch	5BD5	DEFB $01,$01	loader_load loads two bytes to here. -- unsure what uses them