Nightshade: Routine at C1DB

Used by the routine at NEW_GAME.

At every new game each cell type from 2 to 35 is given 16-31 finds, the low four bits of bytes read from a random place in the first 4K of the ROM, plus 16 (STOCKS). Types 0, open ground, and 1 get none.

Then the third protection check: bit 7 of R must be set. The refresh counter the Z80 keeps in R counts only its low seven bits, so bit 7 changes only when a program loads R, and the loader did (LOADER). A copy started by any other means has it clear, and falls into RESET, which jumps to address 0: the Spectrum starts again as if just switched on. NEW_LIFE jumps to RESET as well when its own check fails.

Used by the routine at NEW_GAME. At every new game each cell type from 2 to 35 is given 16-31 finds, the low four bits of bytes read from a random place in the first 4K of the ROM, plus 16 (STOCKS). Types 0, open ground, and 1 get none. Then the third protection check: bit 7 of R must be set. The refresh counter the Z80 keeps in R counts only its low seven bits, so bit 7 changes only when a program loads R, and the loader did (LOADER). A copy started by any other means has it clear, and falls into RESET, which jumps to address 0: the Spectrum starts again as if just switched on. NEW_LIFE jumps to RESET as well when its own check fails.
STOCK_BUILDINGS	C1DB	CALL NEXT_TURN	count a turn, and stir the random number
	C1DE	LD HL,(RANDOM)	HL = somewhere in the first 4K of the ROM
	C1E1	LD A,H
	C1E2	AND $0F
	C1E4	LD H,A
	C1E5	LD DE,$BBD0	16-31 for each type from 2 to 35
	C1E8	LD B,$22
STOCK_BUILDINGS_0	C1EA	LD A,(HL)
	C1EB	INC HL
	C1EC	AND $0F
	C1EE	OR $10
	C1F0	LD (DE),A
	C1F1	INC DE
	C1F2	DJNZ STOCK_BUILDINGS_0
	C1F4	LD A,R	protection check 3: R's bit 7, the loader's mark, still set: carry on
	C1F6	BIT 7,A
	C1F8	RET NZ
This entry point is used by the routine at NEW_LIFE.
RESET	C1F9	XOR A	RESET: start the Spectrum again (never ran in the sessions)
	C1FA	LD L,A
	C1FB	LD H,A
	C1FC	JP (HL)