; FLASH GORDON driver
; Copyright 2012, Adrien Destugues <pulkomandy@gmail.com>
; This program is distributed under the terms of the MIT licence

; Start here.
	DI

	LD HL, 0xC9FB
	LD (0x38), HL

; Move the screen to $8000 or $0000 so we can display things to the user, while
; C000 will write to the ROM and 4000 will hold the data to write... That could
; get a bit messy so maybe we will need to use the screen at 4000 as a buffer
; for the ROM data as well. Or just use a bank for that ?
	; TODO

; Map the ROM in
	LD BC, 0x7F85
	OUT (C),C

; ask the user to enable writing
	; TODO

; Turns out with the MegaFlash design, we can't both read and write. When the
; memory is in write mode, reading is disabled. This means we can't identify
; the chip, or use the data polling features. And we have to go for the
; worst-case timing given in the datasheet :(

; ... anyway, start with erasing the sectors we need.
	LD B, 4
ERASE
	PUSH BC

	LD A, 0x80 ; ERASE
	CALL send_command

	CALL prepare_command
	
	LD B,0xDF
	LD C,5 ; ROM number to write (FIXME get it as a RSX param)
	OUT (C),C

	; Compute address near start of sector
	POP BC
	LD A,B
	DEC A
	SLA A
	SLA A
	
	ADD 0xC0

	LD H,A

	LD E, 0x30
	LD (HL), E

	; This will delay long enough - we need at least 25ms
	EI
	HALT
	HALT
	HALT
	HALT
	DI

	DJNZ ERASE

; Ok, now that we erased the 4 sectors we needed, we can write data to them
	LD HL, 0xC000
	LD IX, 0x4000
PROGRAM
	LD A, 0xA0 ; BYTE PROGRAM ;	2	10
	PUSH HL					  ;	3	13
	CALL send_command		  ; 5	18

	LD B,0xDF
	LD C,5 ; ROM number to write (FIXME get it as a RSX param)
	OUT (C),C

	POP HL

	LD A,(IX + 0)
	LD (HL),A		; Write occurs here. Need to wait 20 NOPs before next
					; operation on ROM. Our code is slow enough already !

	INC IX					;	3	5
	INC HL					;	2	2

	LD A,H
	OR L

	JR NZ, PROGRAM			;	3	8

	JR $

; Now reuse and adapt the code from OUL guys !
	; TODO

; That's all folks !
	RET

; Helper routines -----------------------------------------------------

; Send a command to the ROM. The available commands are :
;ERASE		equ	0x80
IDENTIFY	equ	0x90
BYTEPROG	equ 0xA0
RESET		equ	0xF0

; Input: Commend to send in A register
send_command:
	; That code is shared with sector erase which has some tricks
	call prepare_command

	; Select ROM 1 again and write the command to address 0xEAAA
	INC C
	OUT (C),C
	EX DE,HL
	LD (HL), A

	; Select ROM 0xFF, which basically prevents future accesses to get to the
	; Flash chip.
	DEC C
	DEC C
	OUT (C),C

	RET

prepare_command:
	; Select ROM 1
	LD BC,0xDF01
	LD HL,0xD555
	LD DE,0xEAAA

	; Select ROM 1 and write 0xAA to address 0xD555
	OUT (C),C
	LD (HL),E

	; Select ROM 2 and write 0x55 to address 0xEAAA
	DEC C
	OUT (C),C
	EX DE,HL
	LD (HL), E

	RET


; Print value of A, as 2 hex digits
printhex
	PUSH	AF
	RRA	
	RRA	
	RRA	
	RRA		;divise A par 8 
	CALL	PRNHEX1	;affiche le premier morceau
	POP	AF	;r{cup la valeur originale pour la suit
PRNHEX1			;affiche la valeur de A sur 1 chiffre
;affiche A sur 1 chiffre en Hexa
	AND	0xF	;ne prend que les unit{s
	OR	A
	DAA		;convertit en d{cimal  
	ADD	A,0xF0	;ajoute 240
	ADC	A,0x40	;ajoute 64+le carry (si >15)
;on a le code ascii du chiffre @ afficher
	JP	0xBB5A	;call-ret
;