first working vm

README.md

@@ -2,50 +2,44 @@
 
 very early days for now.
 
-in the racket repl:
+in the racket repl (comments for reader comprehension, remove before running):
 
 ```
- (run-lines (list
+(run-vm #x150 #x150 #x16 ; start-address, end-memory-view-addr, number-bytes-view
-  (8b-ld-reg-imm 4 #x01)
+   '(#x3E #x69           ; LD A, $69
-  (8b-ld-reg-imm 5 #x50)
+     #x26 #x01           ; LD H, $01
-  (8b-ld-reg-imm 7 #x69)
+     #x2E #x62           ; LD L, $62
-  (8b-ld-reg-reg 6 7)
+     #x77                ; LD (HL), A
-  (8b-ld-reg-reg 7 4)
+     #x2E #x5B           ; LD L, $5B
-  (8b-ld-reg-imm 5 #x51)
+     #x36 #xE6           ; LD (HL), $E6  ($E6 is the opcode for XOR $xx)
-  (8b-ld-reg-reg 6 7)))
+     #x10                ; STOP          (this instruction @ address $015B)
+     #xF0                ;               (non-instruction, will be arg for previous byte)
+     #x2E #x63           ; LD L, $63
+     #x77                ; LD (HL), A
+     #x10                ; STOP
+     ))
 ```
 
 will evaluate to:
 
 ```
-PC: $07, SP: $00, Flags: %00000000
+PC: $16, SP: $00, Flags: %00000000
 BC: $0000, DE: $0000
-HL: $0151, AF: $0100
+HL: $0163, AF: $6000
-(HL): $01
+(HL): $60
-$0150 > $69 $01 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 < $0160
+$0150 > $3e $69 $26 $01 $2e $62 $77 $2e $5b $36 $e6 $e6 $f0 $2e $63 $77 $10 $00 $69 $60 $00 $00 < $0165
 ```
 
-which is the equivilent of:
+here we can see the program loaded starting from address `$0150`, including the `XOR` instruction loaded to `$015B` during execution, and the `$69` we loaded to memory, along with the result of `XOR $F0` we loaded to memory, at `$0162` and `$0163` respectively.
 
-```
+## notes
-LD H, $01
-LD L, $50
-LD A, $69
-LD (HL), A
-LD A, H
-LD L, $51
-LD (HL), A
-```
 
-# notes
+currently supported instructions are:
-
+   * `LD [reg], #imm`
-register numbering is following how the LR35902 decodes instructions, as such:
+   * `LD [reg], [reg]`
-
+   * `XOR #imm`
-   * 0: B
+   * `AND #imm`
-   * 1: C
+   * `OR #imm`
-   * 2: D
+   * `STOP`
-   * 3: E
+   * `NOP`
-   * 4: H
+all other instructions treated as `NOP`
-   * 5: L
-   * 6: (HL)
-   * 7: A

vm.rkt

@@ -3,12 +3,13 @@
 (struct mem
    (regs pc sp flags bank))
 
-(define (make-mem)
+(define (make-mem [start #x00] [bs '()])
+   (set-bytes start bs
       (mem (make-regs)
+           start
            0
            0
-        0
+           (make-bank))))
-        (make-bank)))
 
 (define (make-regs)
    (make-vector 8 0))
@@ -38,8 +39,8 @@
                  (struct-copy mem m [bank newbank]))))
        (error "unknown register index")))
 
-(define (make-bank)
+(define (make-bank [def #x00])
-   (make-vector 65536 #x00))
+   (make-vector 65536 def))
 
 (define (mod-8bit val)
    (modulo val 256))
@@ -51,6 +52,10 @@
    (begin
       (struct-copy mem m [pc (mod-16bit addr)])))
 
+(define (set-flags f m)
+   (begin
+      (struct-copy mem m [flags (mod-8bit f)])))
+
 (define (get-byte addr m)
    (let ([b (mem-bank m)])
       (if (and (>= addr 0)
@@ -74,16 +79,50 @@
                   (cdr bs)
                   (set-byte addr (car bs) m))))
 
+(define (get-x byte)
+   (arithmetic-shift (bitwise-and #b11000000 byte) -6))
+
+(define (get-y byte)
+   (arithmetic-shift (bitwise-and #b00111000 byte) -3))
+
+(define (get-z byte)
+   (bitwise-and #b00000111 byte))
+
 (define (inc-sp m)
    (struct-copy mem m [sp (add1 (mem-sp m))]))
 
 (define (inc-pc m)
    (struct-copy mem m [pc (add1 (mem-pc m))]))
 
-
 (define (make-16b-addr x y)
    (bitwise-ior y (arithmetic-shift x 8)))
 
+(define (make-8b-ld-reg-imm y m)
+   (letrec ([pc (mem-pc m)]
+            [x (get-byte pc m)])
+      (cons (8b-ld-reg-imm y x)
+            (set-pc (add1pc pc) m))))
+
+(define (make-8b-ld-reg-reg y z m)
+  (cons (8b-ld-reg-reg y z)
+        m))
+
+(define (make-alu-imm z m)
+   (letrec ([pc (mem-pc m)]
+            [x (get-byte pc m)])
+    (cons (case z
+            [(4) (8b-and-imm x)]
+            [(5) (8b-xor-imm x)]
+            [(6) (8b-or-imm x)]
+            [else (nop)])
+         (inc-pc m))))
+
+(define (make-nop m)
+  (cons (nop) m))
+
+(define (make-stop m)
+   (cons 'STOP m))
+
 (define (8b-ld-reg-imm reg imm)
    (lambda (m)
       (set-reg reg imm m)))
@@ -94,6 +133,33 @@
                (get-reg src m)
                m)))
 
+(define (8b-xor-imm imm)
+   (lambda (m)
+      (let ([a (bitwise-xor (get-reg 7 m)
+                            (mod-8bit imm))])
+         (displayln (format "~a xor ~a = ~a" (display-byte-hex (get-reg 7 m))
+                                             (display-byte-hex (mod-8bit imm))
+                                             a))
+         (set-flags (if (= a 0) #b10000000 #x00)
+            (set-reg 7 a m)))))
+
+(define (8b-or-imm imm)
+   (lambda (m)
+      (let ([a (bitwise-ior (get-reg 7 m)
+                            (mod-8bit imm))])
+         (set-flags (if (= a 0) #b10000000 #x00)
+            (set-reg 7 a m)))))
+
+(define (8b-and-imm imm)
+   (lambda (m)
+      (let ([a (bitwise-and (get-reg 7 m)
+                            (mod-8bit imm))])
+         (set-flags (if (= a 0) #b10000000 #x00)
+            (set-reg 7 a m)))))
+
+(define (nop)
+   (lambda (m) m))
+
 (define (display-byte-hex v)
   (~a #:align 'right #:left-pad-string "0" #:width 2
       (format "~x" v)))
@@ -134,7 +200,7 @@
    (define (print-mem v)
       (display (format " $~a" (display-byte-hex v))))
    (let ([s (display-word-hex start)]
-         [e (display-word-hex (mod-16bit (+ start count)))])
+         [e (display-word-hex (mod-16bit (+ start (sub1 count))))])
       (display (format "$~a >" s))
       (let ([splice (vector-take
                        (vector-drop (mem-bank m) start)
@@ -143,6 +209,46 @@
       (display (format " < $~a\n" e) ))
       (void))
 
+(define (add1pc pc)
+   (mod-16bit (add1 pc)))
+
+(define (within x y z)
+   (and (>= x y) (<= x z)))
+
+(define (decode-op m)
+   (letrec ([pc (mem-pc m)]
+            [op (get-byte pc m)]
+            [npc (add1pc pc)]
+            [x (get-x op)]
+            [y (get-y op)]
+            [z (get-z op)])
+      (cond
+         [(= #x00 op) (make-nop (set-pc npc m))]
+         [(= #x10 op) (make-stop (set-pc npc m))]
+         [(= 1 x)
+            (make-8b-ld-reg-reg y z (set-pc npc m))]
+         [(and (= 3 x) (within z 4 6))
+            (make-alu-imm y (set-pc npc m))]
+         [(and (= 0 x) (= 6 z))
+            (make-8b-ld-reg-imm y (set-pc npc m))]
+         [else (make-nop (set-pc npc m))])))
+
+(define (run-vm start bank-start bank-count bs)
+   (let ([m (make-mem start bs)])
+      (define (fin m)
+         (begin (print-state m)
+                (print-regs m)
+                (print-part-bank bank-start bank-count m)))
+      (define (run-op m)
+         (letrec ([op-pc (decode-op m)]
+                  [op (car op-pc)]
+                  [newmem (cdr op-pc)])
+            (if (and (not (procedure? op))
+                     (eq? op 'STOP))
+                (fin newmem)
+                (run-op (op newmem)))))
+      (run-op m)))
+
 (define (run-lines ls)
    (define (run-line-help ls m)
       (if (null? ls)