first working vm
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README.md
64
README.md
@ -2,50 +2,44 @@
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very early days for now.
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in the racket repl:
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in the racket repl (comments for reader comprehension, remove before running):
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```
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(run-lines (list
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(8b-ld-reg-imm 4 #x01)
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(8b-ld-reg-imm 5 #x50)
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(8b-ld-reg-imm 7 #x69)
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(8b-ld-reg-reg 6 7)
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(8b-ld-reg-reg 7 4)
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(8b-ld-reg-imm 5 #x51)
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(8b-ld-reg-reg 6 7)))
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(run-vm #x150 #x150 #x16 ; start-address, end-memory-view-addr, number-bytes-view
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'(#x3E #x69 ; LD A, $69
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#x26 #x01 ; LD H, $01
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#x2E #x62 ; LD L, $62
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#x77 ; LD (HL), A
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#x2E #x5B ; LD L, $5B
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#x36 #xE6 ; LD (HL), $E6 ($E6 is the opcode for XOR $xx)
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#x10 ; STOP (this instruction @ address $015B)
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#xF0 ; (non-instruction, will be arg for previous byte)
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#x2E #x63 ; LD L, $63
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#x77 ; LD (HL), A
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#x10 ; STOP
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))
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```
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will evaluate to:
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```
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PC: $07, SP: $00, Flags: %00000000
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PC: $16, SP: $00, Flags: %00000000
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BC: $0000, DE: $0000
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HL: $0151, AF: $0100
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(HL): $01
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$0150 > $69 $01 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 $00 < $0160
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HL: $0163, AF: $6000
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(HL): $60
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$0150 > $3e $69 $26 $01 $2e $62 $77 $2e $5b $36 $e6 $e6 $f0 $2e $63 $77 $10 $00 $69 $60 $00 $00 < $0165
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```
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which is the equivilent of:
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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.
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```
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LD H, $01
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LD L, $50
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LD A, $69
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LD (HL), A
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LD A, H
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LD L, $51
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LD (HL), A
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```
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## notes
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# notes
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register numbering is following how the LR35902 decodes instructions, as such:
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* 0: B
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* 1: C
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* 2: D
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* 3: E
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* 4: H
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* 5: L
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* 6: (HL)
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* 7: A
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currently supported instructions are:
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* `LD [reg], #imm`
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* `LD [reg], [reg]`
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* `XOR #imm`
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* `AND #imm`
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* `OR #imm`
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* `STOP`
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* `NOP`
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all other instructions treated as `NOP`
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126
vm.rkt
126
vm.rkt
@ -3,12 +3,13 @@
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(struct mem
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(regs pc sp flags bank))
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(define (make-mem)
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(mem (make-regs)
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0
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0
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0
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(make-bank)))
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(define (make-mem [start #x00] [bs '()])
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(set-bytes start bs
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(mem (make-regs)
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start
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0
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0
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(make-bank))))
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(define (make-regs)
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(make-vector 8 0))
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@ -38,8 +39,8 @@
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(struct-copy mem m [bank newbank]))))
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(error "unknown register index")))
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(define (make-bank)
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(make-vector 65536 #x00))
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(define (make-bank [def #x00])
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(make-vector 65536 def))
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(define (mod-8bit val)
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(modulo val 256))
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@ -51,6 +52,10 @@
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(begin
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(struct-copy mem m [pc (mod-16bit addr)])))
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(define (set-flags f m)
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(begin
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(struct-copy mem m [flags (mod-8bit f)])))
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(define (get-byte addr m)
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(let ([b (mem-bank m)])
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(if (and (>= addr 0)
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@ -74,16 +79,50 @@
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(cdr bs)
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(set-byte addr (car bs) m))))
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(define (get-x byte)
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(arithmetic-shift (bitwise-and #b11000000 byte) -6))
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(define (get-y byte)
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(arithmetic-shift (bitwise-and #b00111000 byte) -3))
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(define (get-z byte)
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(bitwise-and #b00000111 byte))
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(define (inc-sp m)
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(struct-copy mem m [sp (add1 (mem-sp m))]))
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(define (inc-pc m)
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(struct-copy mem m [pc (add1 (mem-pc m))]))
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(define (make-16b-addr x y)
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(bitwise-ior y (arithmetic-shift x 8)))
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(define (make-8b-ld-reg-imm y m)
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(letrec ([pc (mem-pc m)]
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[x (get-byte pc m)])
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(cons (8b-ld-reg-imm y x)
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(set-pc (add1pc pc) m))))
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(define (make-8b-ld-reg-reg y z m)
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(cons (8b-ld-reg-reg y z)
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m))
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(define (make-alu-imm z m)
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(letrec ([pc (mem-pc m)]
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[x (get-byte pc m)])
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(cons (case z
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[(4) (8b-and-imm x)]
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[(5) (8b-xor-imm x)]
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[(6) (8b-or-imm x)]
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[else (nop)])
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(inc-pc m))))
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(define (make-nop m)
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(cons (nop) m))
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(define (make-stop m)
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(cons 'STOP m))
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(define (8b-ld-reg-imm reg imm)
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(lambda (m)
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(set-reg reg imm m)))
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@ -94,6 +133,33 @@
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(get-reg src m)
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m)))
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(define (8b-xor-imm imm)
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(lambda (m)
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(let ([a (bitwise-xor (get-reg 7 m)
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(mod-8bit imm))])
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(displayln (format "~a xor ~a = ~a" (display-byte-hex (get-reg 7 m))
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(display-byte-hex (mod-8bit imm))
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a))
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(set-flags (if (= a 0) #b10000000 #x00)
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(set-reg 7 a m)))))
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(define (8b-or-imm imm)
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(lambda (m)
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(let ([a (bitwise-ior (get-reg 7 m)
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(mod-8bit imm))])
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(set-flags (if (= a 0) #b10000000 #x00)
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(set-reg 7 a m)))))
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(define (8b-and-imm imm)
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(lambda (m)
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(let ([a (bitwise-and (get-reg 7 m)
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(mod-8bit imm))])
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(set-flags (if (= a 0) #b10000000 #x00)
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(set-reg 7 a m)))))
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(define (nop)
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(lambda (m) m))
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(define (display-byte-hex v)
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(~a #:align 'right #:left-pad-string "0" #:width 2
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(format "~x" v)))
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@ -134,7 +200,7 @@
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(define (print-mem v)
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(display (format " $~a" (display-byte-hex v))))
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(let ([s (display-word-hex start)]
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[e (display-word-hex (mod-16bit (+ start count)))])
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[e (display-word-hex (mod-16bit (+ start (sub1 count))))])
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(display (format "$~a >" s))
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(let ([splice (vector-take
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(vector-drop (mem-bank m) start)
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@ -143,6 +209,46 @@
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(display (format " < $~a\n" e) ))
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(void))
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(define (add1pc pc)
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(mod-16bit (add1 pc)))
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(define (within x y z)
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(and (>= x y) (<= x z)))
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(define (decode-op m)
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(letrec ([pc (mem-pc m)]
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[op (get-byte pc m)]
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[npc (add1pc pc)]
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[x (get-x op)]
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[y (get-y op)]
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[z (get-z op)])
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(cond
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[(= #x00 op) (make-nop (set-pc npc m))]
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[(= #x10 op) (make-stop (set-pc npc m))]
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[(= 1 x)
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(make-8b-ld-reg-reg y z (set-pc npc m))]
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[(and (= 3 x) (within z 4 6))
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(make-alu-imm y (set-pc npc m))]
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[(and (= 0 x) (= 6 z))
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(make-8b-ld-reg-imm y (set-pc npc m))]
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[else (make-nop (set-pc npc m))])))
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(define (run-vm start bank-start bank-count bs)
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(let ([m (make-mem start bs)])
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(define (fin m)
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(begin (print-state m)
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(print-regs m)
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(print-part-bank bank-start bank-count m)))
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(define (run-op m)
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(letrec ([op-pc (decode-op m)]
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[op (car op-pc)]
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[newmem (cdr op-pc)])
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(if (and (not (procedure? op))
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(eq? op 'STOP))
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(fin newmem)
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(run-op (op newmem)))))
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(run-op m)))
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(define (run-lines ls)
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(define (run-line-help ls m)
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(if (null? ls)
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