path: root/programs/subasm.s

; SuBAsm
; The Sux Bootstrapped Assembler.
;
; by mr b0nk 500 <b0nk@b0nk.xyz>

; Variables
.org $1000
prg_name:
	.byte "SuBAsm"
ver_txt:
	.byte ", version "
ver_num:
	.byte "0.1"

; Directives.
dir:
	.byte "org"
	.byte "byte"
	.byte "word"
	.byte "dword"
	.byte "qword"

; Instruction mnemonics.
mne:
	.byte "CPS"
	.byte "ADC"
	.byte "AAB"
	.byte "PHB"
	.byte "PHP"
	.byte "PHA"
	.byte "PHY"
	.byte "TAY"
	.byte "PHX"
	.byte "TAX"
	.byte "TYX"
	.byte "JMP"
	.byte "SBC"
	.byte "SAB"
	.byte "PLB"
	.byte "PLP"
	.byte "PLA"
	.byte "PLY"
	.byte "TYA"
	.byte "PLX"
	.byte "TXA"
	.byte "TXY"
	.byte "JSR"
	.byte "AND"
	.byte "ABA"
	.byte "STT"
	.byte "TAB"
	.byte "TSX"
	.byte "BPO"
	.byte "ORA"
	.byte "OAB"
	.byte "TBA"
	.byte "SEI"
	.byte "TXS"
	.byte "BNG"
	.byte "XOR"
	.byte "XAB"
	.byte "CLI"
	.byte "BCS"
	.byte "LSL"
	.byte "LLB"
	.byte "STB"
	.byte "SEC"
	.byte "STA"
	.byte "STY"
	.byte "STX"
	.byte "BCC"
	.byte "LSR"
	.byte "LRB"
	.byte "LDB"
	.byte "CLC"
	.byte "LDA"
	.byte "LDY"
	.byte "LDX"
	.byte "BEQ"
	.byte "ROL"
	.byte "RLB"
	.byte "SSP"
	.byte "BNE"
	.byte "ROR"
	.byte "RRB"
	.byte "CSP"
	.byte "BVS"
	.byte "MUL"
	.byte "MAB"
	.byte "SEV"
	.byte "BVC"
	.byte "DIV"
	.byte "DAB"
	.byte "CLV"
	.byte "RTS"
	.byte "CMP"
	.byte "CAB"
	.byte "CPY"
	.byte "CPX"
	.byte "CPB"
	.byte "ENT"
	.byte "RTI"
	.byte "INC"
	.byte "IAB"
	.byte "INY"
	.byte "INX"
	.byte "DEC"
	.byte "DBA"
	.byte "DEY"
	.byte "DEX"
	.byte "WAI"
	.byte "JSL"
	.byte "ASR"
	.byte "ARB"
	.byte "NOP"
	.byte "RTL"
	.byte "BRK"


scr_row:
	.byte $0
scr_col:
	.byte $0
a:
	.word $0
b:
	.word $0
c:
	.word $0
d:
	.word $0

str_buf:

; Input buffer.
.org $2000
buf:

.org $2400
ptr1:
	.qword $2500

ptr2:
	.qword $2900

; Control Register.
.org $C000
ctrl_reg:

; Screen.
.org $C001
scr:

; Keyboard.
.org $C002
kbd:

; Main program.
.org $0
reset:
	cps
	ldx.w #$FFFF
	txs
	ldy #0
	jsr clr_buf
	ldx.w #0	; Reset x.
	ldy #0		; Reset y.
	jmp print_title

read:
	lda ctrl_reg	; Is the keyboard ready?
	beq read	; Loop until the keyboard is ready.
	lda #0		; Start resetting the control register.
	sta ctrl_reg	; Reset the control register.
	jmp getchar	; We got a key.

rset_x:

	ldx #0		; Reset x.
	stx.w x
	rts

print_title:
	lda prg_name, x
	beq print_ver	; Did we find a null terminator?
	sta		; Print character.
	inx		; Increment offset.
	inc x
	jmp print_title	; Keep printing more characters.

print_ver
	jsr rset_x
	lda ver_txt, x
	beq print_num	; Did we find a null terminator?
	sta scr		; Print character.
	inx		; Increment offset.
	jmp print_ver	; Keep printing more characters.

print_num:
	lda ver_num, x
	beq getline	; Did we find a null terminator?
	sta scr		; Print character.
	inx		; Increment offset.
	jmp print_num	; Keep printing more characters.
getline:
	lda #$A
	sta scr		; Print newline
	inc scr_row
	lda #0
	sta scr_col
	inc y
	jsr rset_x
	jmp read

getchar:
	lda kbd		; Get typed character.
	cmp #$1B	; Did the user type an escape?
	beq esc		; Yes, so start getting the escape code.
	cmp #$A		; Did the user type a newline?
	beq nl		; Yes, so start parsing the input.
	cmp #8		; Did the user type a backspace?
	beq bs		; Yes, so start checking the buffer.
	jsr echo	; Print character to screen.

store_char:
	sta buf, y	; Store typed character into the input buffer.
	iny		; Increment buffer offset.
	jmp read	; Get another character.

esc:
	lda ctrl_reg	; Skip the '['.
	lda ctrl_reg	; Get the next character.
	beq read	; We have an error, so discard it, and go back to getting user input.
	lda kbd		; Get the escape code.
	sta c		; Store the escape code, until we need it.
	jsr isup	; Check if the user pressed up.
	lda d
	cmp #0
	bne esc_end
	jsr isdown	; Check if the user pressed down.
	lda d
	cmp #0
	bne esc_end
	lda #0
	jsr isleft	; Check if the user pressed left.
	lda d
	cmp #0
	bne esc_end
	jsr isright	; Check if the user pressed right.
esc_end:
	lda #$0
	sta d
	jmp rset_a	; Go back to getting user input.

isup:
	lda scr_row	; Is the cursor at the top of the screen?
	beq isup_done	; Yes, so return.
	lda c		; No, so load the escape code back into the accumulator.
	cmp #$41	; Did the user press the up arrow key?
	beq up		; Yes, so move the cursor up.
isup_done:
	rts		; End of isup.

isdown:
	lda scr_row	; Start checking the y coordinate of the cursor.
	cmp #$17	; Is the cursor at the bottom of the screen?
	beq isdown_done	; Yes, so return.
	lda c		; No, so load the escape code back into the accumulator.
	cmp #$42	; Did the user press the down arrow key?
	beq down	; Yes, so move the cursor down.
isdown_done:
	rts		; End of isdown.

isright:
	lda scr_col	; Start checking the x coordinate of the cursor.
	cmp #$4F	; Is the cursor at the far right of the screen?
	beq isright_end	; Yes, so return.
	lda c		; No, so load the escape code back into the accumulator.
	cmp #$43	; Did the user press the right arrow key?
	beq right	; Yes, so move the cursor right.
isright_end:
	rts		; End of isright.

isleft:
	lda scr_col	; Is the cursor at the far left of the screen?
	beq isleft_done	; Yes, so return.
	lda c		; No, so load the escape code back into the accumulator.
	cmp #$44	; Did the user press the left arrow key?
	beq left	; Yes, so move the cursor left.
isleft_done:
	rts		; End of isleft.

up:
	dec scr_row
	jsr update_pos
	lda #1
	sta d
	jmp isup_done
down:
	inc scr_row
	jsr update_pos
	lda #1
	sta d
	jmp isdown_done
right:
	inc scr_col
	jsr update_pos
	jmp isright_end
left:
	dec scr_col
	jsr update_pos
	lda #1
	sta d
	jmp isleft_done

update_pos:
	lda #$1B	; Print an escape character
	sta scr		; to the screen.
	lda #$5B	; Print '['
	sta scr		; to the screen, and start the escape sequence.
	jsr getrow	; Start printing the row number to the screen.
	jsr getcol	; Start printing the column number to the screen.
	lda #$48	; Print 'H'
	sta scr		; to the screen.
	rts		; End of update_pos.
getrow:
	lda scr_row	; Get the cursor's y coordinate.
	div #$A		; Divide A by 10.
	adc #$30	; Convert it to ascii, and
	sta scr		; print to the screen.
	tba		; Get the remainder.
	adc #$30	; Convert it to ascii, and
	sta scr		; print to the screen.
	rts		; End of getrow.
getcol:
	lda #$3B	; Print ';'
	sta scr		; to the screen.
	lda scr_col	; Get the cursor's x coordinate.
	div #$A		; Divide A by 10.
	adc #$30	; Convert it to ascii, and
	sta scr		; print to the screen.
	tba		; Get the remainder.
	adc #$30	; Convert it to ascii, and
	sta scr		; print to the screen.
	rts		; End of getrow.



nl:
	sta scr		; Print newline.
	inc scr_row	; Move the cursor down one line.
	lda #0		; Put a null terminator, in place of the newline.
	sta scr_col	; Move the cursor back to column 0.
	sta buf, y	; Place it into the input buffer.
	ldy.w #0	; Reset y, to parse the input.
	jsr parse	; Start parsing input.

back:
	sta scr		; Print backspace.
	lda #0		; Put a null terminator, in place of the backspace.
	sta buf, y	; Place it into the input buffer.
	dey		; Decrement buffer offset.
	dec scr_col
	jmp read	; Get next character.

bs:
	cpy #0		; Are we at the start of the buffer?
	beq read	; We are, so do not store the backspace into the buffer.
	jmp back	; We are not, so add the backspace to the buffer.

parse:
	jsr getdir
	jsr
	rts

getdir:
	iny		; Increment offset.
	lda buf, y
	jsr iswhite
	bcs getdir	; Reset y, if we hit the null terminator.
	cmp #$2E	; Is this character a '.'?
	bne getdir_exit	; No, so return.
	jsr clr_ptr

getdir_end:
	iny		; Increment offset.
	lda buf, y
	jsr iswhite
	bcs getdir_cmp
	ora #%00100000	; Make character lower case.
	sta (ptr1), y
	jmp getdir_end
gettok:
	ply #1
	iny
gettok2:
	lda buf, y
	jsr istoken
	bcs gettok3
	jmp gettok2
gettok3:
	cmp #$
	cmp #$24	; Is this character, a '$'?
	beq getaddr	; Yes, so start getting the address.



getdir_cmp:
	phy #1
	ldy.w #0
	tyx
getdir_cpl:
	ldb dir, x	; Start checking if the directive we're using, is "org".
	stb (ptr2), y
	beq getdir_scmp
	inx
	iny
	jmp getdir_cpl
getdir_scmp:
	ldy #0
	jsr strcmp
	cpx #0
	beq getdir_tok
getdir_exit:
	rts		; End of getdir.


istoken:
	cmp #$20	; Is this character a space?
	beq istoken_f	; Yes, so return false.
	cmp #$09	; Is this character a tab?
	beq istoken_f	; Yes, so return false.
	cmp #$A		; Is this character a newline?
	beq istoken_f	; Yes, so return false.
	cmp #$3B	; Is this character a ';'?
	beq istoken_f	; Yes, so return false.
	cmp #0		; Is this character a null terminator?
	beq istoken_f	; Yes, so return false.
	sec		; Return true.
	rts		; End of istoken.
istoken_f
	clc		; Return false.
	rts		; End of istoken_f.

iswhite:
	cmp #$20	; Is this character a space?
	beq iswhite_t	; Yes, so return true.
	cmp #9		; Is this character a tab?
	beq iswhite_t	; Yes, so return true.
	clc		; No, so return false.
	rts		; End of iswhite.
iswhite_t:
	sec		; Return true.
	rts		; End of iswhite_t.

rset_y:
	ldy.w #0
	jmp print_buf	; Print the input buffer.

print_buf:
	lda buf, y	; Get a character from the input buffer.
	beq fin		; Are we done with printing the buffer?
	sta scr		; Print said character.
	iny
	jmp print_buf	; Keep printing the buffer.

spin:
	nop
	nop
	nop
	jmp spin

clr_buf:
	lda #0
	cpy.w #$3FF
	beq clr_end
	sta buf, y
	iny
	jmp clr_buf
clr_sbuf:
	lda #0
	cpy.w #$1FF
	beq clr_end
	sta str_buf, y
	iny
	jmp clr_sbuf

clr_end:
	rts

echo:
	tab
	ldx scr_col
	cpx #$4F
	bne echo_print
	cmp #$A
	beq linewrap
linewrap:
	inc scr_row
	ldx #0
	stx scr_col
	jsr update_pos
echo_print:
	tba
	sta scr		; Echo typed character.
	inc scr_col	; Increment the cursor's x coordinate.
	sta buf, y	; Store typed character into the input buffer.
	iny		; Increment the buffer offset.
	rts		; Return.

clr_ptr:
	lda #0
	cpy.w #$3FF
	beq ptr_end
	sta (ptr1), y
	sta (ptr2), y
	iny
	jmp clr_ptr
ptr_end:
	rts

strcmp:
	lda (ptr1), y
	cmp (ptr2), y
	bne strcmp_l1
	tax
	beq strcmp_l3
	iny
	bne strcmp
	jmp strcmp


strcmp_l1:
	bcs strcmp_l2
	ldx #0
	dex
	rts

strcmp_l2:
	ldx #1
strcmp_l3:
	rts


.org $FFC0
.qword reset

.org $FF50
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin

.org $FFA0
.qword irq_routine
.org $0
v
.org $100
v
.org $200
v
.org $300
v
.org $1000
v
.org $1100
v
.org $1200
v
.org $1300
v
.org $1400
v
q