From 7a8b8ec34148d48b9f420fa45e42829d57783d51 Mon Sep 17 00:00:00 2001
From: Alexandre Dumont <adumont@gmail.com>
Date: Fri, 21 May 2021 18:11:59 +0200
Subject: [PATCH] First forth attempt

---
 forth/forth00.asm | 204 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 204 insertions(+)
 create mode 100644 forth/forth00.asm

diff --git a/forth/forth00.asm b/forth/forth00.asm
new file mode 100644
index 0000000..3a1f1ce
--- /dev/null
+++ b/forth/forth00.asm
@@ -0,0 +1,204 @@
+; FORTH 
+; Alex Dumont
+
+; Help & Reference:
+; [Bitwise, Day 35: Implementing Forth](https://www.youtube.com/watch?v=rlayTh3sjiw)
+; [Moving Forth: Part 1](https://www.bradrodriguez.com/papers/moving1.htm)
+
+
+; IP: Next Instruction Pointer (IP)-->W
+; W : Address of the code to run
+W	.= $FE		; 2 bytes, an address
+IP	.= W -2
+DTOP	.= IP-2
+
+	*= $8000
+
+RES_vec
+   	CLD             ; clear decimal mode
+    	LDX #$FF
+    	TXS             ; set the stack pointer
+    	LDX #DTOP
+    	CLI
+
+	LDA #<lbl_test1
+	STA IP
+	LDA #>lbl_test1
+	STA IP+1
+
+
+NEXT: 	.MACRO
+; (IP) --> W
+	LDY #0
+	LDA (IP),y
+	STA W
+	INY
+	LDA (IP),y
+	STA W+1
+; IP+2 --> IP
+	CLC
+	LDA IP
+	ADC #2		; A<-A+2
+	STA IP
+	BCC .skip
+	INC IP+1
+.skip:
+; JMP (W)
+	JMP (W)
+	.ENDM
+	
+	NEXT
+	
+	
+	
+	*= $4000
+lbl_test1:	
+	.DW forth_prog
+	
+	*= $4100
+forth_prog:
+	JMP do_COLON
+	.DW do_PUSH1
+	.DW do_DUP
+	.DW do_DROP
+	.DW other_word
+	.DW do_DROP
+	.DW do_SEMI
+
+other_word:
+	JMP do_COLON
+	.DW do_LIT
+	.DW $0002
+	.DW do_LIT
+	.DW $0103
+	.DW do_PLUS
+	.DW do_SWAP
+	.DW do_SEMI
+	
+
+do_COLON: ; COLON aka ENTER
+; push IP to Return Stack
+	LDA IP+1	; HI
+	PHA
+	LDA IP		; LO
+	PHA
+
+; W+3 --> IP 
+; (Code at W was a JMP, so 3 bytes)
+	LDA W+1
+	STA IP+1
+	LDA W
+	ADC #3
+	STA IP
+	BCC skip
+	INC IP+1
+skip:
+	NEXT	
+
+
+; SEMICOLON aka EXIT
+do_SEMI:
+; POP IP from Return Stack
+	PLA
+	STA IP
+	PLA
+	STA IP+1
+; NEXT
+	NEXT
+
+do_SWAP:
+	LDA 2,X
+	LDY 4,X
+	STY 2,X
+	STA 4,X
+	LDA 3,X
+	LDY 5,X
+	STY 3,X
+	STA 5,X
+	NEXT
+
+do_DROP:
+	INX
+	INX
+	NEXT
+
+; FORTH Primitive words
+
+do_PUSH0:
+	STZ 0,x
+	STZ 1,x
+	DEX
+	DEX
+	NEXT
+
+do_PUSH1:
+	LDA #1
+	STA 0,x
+	STZ 1,x
+	DEX
+	DEX
+	NEXT
+
+; Push a literal word (2 bytes)
+do_LIT:
+; (IP) points to literal
+; instead of next instruction ;)
+	LDY #0
+	LDA (IP),y
+	STA 0,X
+	INY
+	LDA (IP),y
+	STA 1,X
+	DEX
+	DEX
+; Now advance IP
+; IP+2 --> IP
+	LDA IP
+	ADC #2
+	STA IP
+	BCC skip1
+	INC IP+1
+skip1:
+	NEXT
+
+do_DUP:
+	LDA 2,X
+	STA 0,X
+	LDA 3,X
+	STA 1,X
+	DEX
+	DEX
+	NEXT	
+
+do_PLUS:
+	CLC
+	INX
+	INX
+	LDA 0,X
+	ADC 2,X
+	STA 2,X
+	LDA 1,X
+	ADC 3,X
+	STA 3,X
+	NEXT
+	
+msg	.BYTE "Monitor v0", 0
+
+IRQ_vec
+NMI_vec
+	RTI
+
+
+	*= $0200
+
+BYTE	.DS 1
+LEN 	.DS 1	; Length of CMD
+CMD	.DS 16	; CMD string
+
+; system vectors
+
+    *=  $FFFA
+
+    .word   NMI_vec     ; NMI vector
+    .word   RES_vec     ; RESET vector
+    .WORD   IRQ_vec     ; IRQ vector
\ No newline at end of file