; Pokemon Mini text engine by Alessandro Lo-Presti (Agilo).


; Write text on the screen using the charmap.
.macro	writestr	a_string

 ; Jump over the following bytes so as to avoid them from being interpreted.
 jmp _afterdata

; Store the string as bytes into memory.
_string:
.db	a_string, 0x7F

; Print the address of _string in the console when compiling.
.printf	"_string (0x%06X) is: %s\n", _string, a_string

_afterdata:

 ; Point HL to the Tile Map data.
 movw	HL, 0x1360

 ; Point BA to the location of the string.
 movw	BA, _string

 ; Skip increments, go to the first letter of the string.
 jmp	_firstletter
_incnext:
 ; Increment pointers to the string/tile map.
 inc	HL
 inc	BA
_firstletter:

 ; Push BA and HL onto the stack to preserve them.
 push	BA
 push	HL

 ; Move the pointer to the string into HL registers.
 ; You can't move a memory address held in BA into a register, HL can.
 movw	HL, BA

 ; Move a byte (letter) from the memory address into a.
 movb   a, [HL]

 ; Subtract 32 from the ASCII character to align with the charmap.
 sub    a, 32

 ; Restore HL.
 pop	HL

 ; Move the letter to the correct tile map.
 movb   [HL], a

 ; Restore BA.
 pop	BA

 ; If the letter isn't the end of the string, go to the next letter.
 cmp	[HL], 0x5F
 jl	_incnext

.endm

 ; Store the address of the image in the memory address register.
 movw   x1, charmap
 
 ; Write the address to a register of the LCD so the PM knows where to look.
 movw   [0x2082], x1

 ; Initialize empty screen. 
 writestr "                                                                                                "