GebVM

GebvM is an 8-bit register-based virtual machine. GebVM has...

Registers There are 8 8-bit registers (R0-R7) that store unsigned values.

Memory There are 65,536 bytes of memory also storing unsigned values. The running program is loaded into memory starting at address 0x0000. A stack occupies the space from 0xFF00 to 0xFFFF.

Bytecode GebVM uses its own bytecode specification. A couple trivial compiled examples are included, and more interesting examples may be added if there is an assembler for the project in the future.

I/O Input, output, and errors are written from/to stdin, stdout, and stderr (respectively).

An Example

These commands and paths can vary with Go version and local settings. This was tested on v1.15.

> # Pull the code
> go get github.com/scottmcleodjr/gebvm
>
> # Run the tests
> go test github.com/scottmcleodjr/gebvm/...
?   	github.com/scottmcleodjr/gebvm	[no test files]
ok  	github.com/scottmcleodjr/gebvm/memory	0.009s
ok  	github.com/scottmcleodjr/gebvm/processor	0.033s
>
> # Build the project
> go build github.com/scottmcleodjr/gebvm
>
> # Run hellow_world.geb
> ./gebvm ~/go/src/github.com/scottmcleodjr/gebvm/examples/hello_world.geb
Hello, World!

Instructions

Instruction	Code	Arguments	Description
No Operation	0x00		Do nothing and continue execution
Move Lit Reg	0x01	Literal, Register	Copy literal value to register
Move Reg Reg	0x02	Source Register, Destination Register	Copy value from source to destination register
Move Lit Memory	0x03	Literal, Pointer Register	Copy literal value to address at pointer register
Move Reg Memory	0x04	Register, Pointer Register	Copy value from register to address at pointer register
Move Memory Reg	0x05	Pointer Register, Register	Copy value from address at pointer register to register
Logical And	0x20	Left Register, Right Register	Set R0 to logical and of values in left and right registers
Logical Or	0x21	Left Register, Right Register	Set R0 to logical or of values in left and right registers
Logical Xor	0x22	Left Register, Right Register	Set R0 to logical xor of values in left and right registers
Logical Bit Clear	0x23	Left Register, Right Register	Set R0 to logical bit clear of values in left and right registers
Logical Shift Left	0x24	Register, Shift Distance	Logical shift left value in register by distance bytes
Logical Shift Right	0x25	Register, Shift Distance	Logical shift right value in register by distance bytes
Inc	0x40	Register	Increment value in register by 1
Dec	0x41	Register	Decrement value in register by 1
Add	0x42	Left Register, Right Register	Set R0 to sum of values in left and right registers
Subtract	0x43	Left Register, Right Register	Set R0 to difference of values in left and right registers
Multiply	0x44	Left Register, Right Register	Set R0 to product of values in left and right registers
Divide	0x45	Left Register, Right Register	Set R0 to quotient of values in left and right registers
Jump	0x60	Address (High Byte, Low Byte)	Set IP to address
JumpEqual	0x61	Register, Address (High Byte, Low Byte)	Set IP to address if values in R0 and register are equal
JumpNotEqual	0x62	Register, Address (High Byte, Low Byte)	Set IP to address if values in R0 and register are not equal
StackPushLit	0x80	Literal	Push literal value onto the stack
StackPushReg	0x81	Register	Push value from register onto the stack
StackPop	0x82	Register	Pop the top value from the stack and store at register
Call	0x83	Address (High Byte, Low Byte)	Function call
Return	0x84		Function return
Print	0xE0	Address (High Byte, Low Byte), Length	Output length chars beginning at address to the writer
ReadInput	0xE1	Register	Store a single char from the reader to register
Halt	0xFF		Halt execution

Notes:

• A pointer register holds the high byte of the address. The sequential next register holds the low byte. R7 cannot be used as a pointer register.
• Registers are represented by the numbers 0x00 (R0) through 0x07 (R7).