16bitvm

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Registers

Name	Description
ip	Instruction pointer
acc	Accumulator
r1	General-purpose
r2	General-purpose
r3	General-purpose
r4	General-purpose
r5	General-purpose
r6	General-purpose
r7	General-purpose
r8	General-purpose
sp	Stack pointer
fp	Frame pointer

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Opcodes

Opcode	Mnemonic	Description	Format
0x10	MOV_LIT_REG	Move literal into register	0x10 [lit_lo] [lit_hi] [reg_id]
0x11	MOV_REG_REG	Move value between registers	0x11 [src_reg_id] [dest_reg_id]
0x12	MOV_REG_MEM	Move register value to memory	0x12 [reg_id] [addr_lo] [addr_hi]
0x13	MOV_MEM_REG	Load memory value into register	0x13 [addr_lo] [addr_hi] [reg_id]
0x14	ADD_REG_REG	Add two registers → acc	0x14 [reg1_id] [reg2_id]
0x15	JMP_NOT_EQ	Jump if acc != value	0x15 [val_lo] [val_hi] [addr_lo] [addr_hi]
0x16	PSH_LIT	Push literal to stack	0x16 [lit_lo] [lit_hi]
0x17	PSH_REG	Push register to stack	0x17 [reg_id]
0x18	POP	Pop from stack to register	0x18 [reg_id]
0x1A	CAL_LIT	Call subroutine at address	0x1A [addr_lo] [addr_hi]
0x5E	CAL_REG	Call subroutine in register	0x5E [reg_id]
0x5F	RET	Return from subroutine	0x5F
0xFF	HLT	Halt execution	0xFF

All literal and address values are 16-bit, little-endian.

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Features

• Memory Mapped I/O: Screen device mapped to 0x3000-0x30FF
• Stack Operations: Push/pop operations with SP and FP registers
• Subroutine Calls: Call and return with state preservation
• Extensible Architecture: Memory mapper for device integration

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Example Memory Layout

Address | Byte | Meaning
--------|------|------------------------------
0x00    | 0x10 | MOV_LIT_REG
0x01    | 0x34 | → r1 = 0x1234
0x02    | 0x12 |
0x03    | 0x04 | (register R1 address)

0x04    | 0x16 | PSH_LIT
0x05    | 0xAB | → push 0xCDAB to stack
0x06    | 0xCD |

0x07    | 0x1A | CAL_LIT
0x08    | 0x20 | → call subroutine at 0x0020
0x09    | 0x00 |

0x0A    | 0xFF | HLT

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Run

go run main.go