Micro VM

The stories created through the official Story Editor using graphical nodes are compiled into a binary executable. This binary is then interpreted by a micro virtual machine embedded in the OpenStory firmware.

Here is a description of that VM.

Registers

name	number	type	call-preserved
r0-r9	0-9	general-purpose	N
t0-t9	10-19	temporary registers	Y
pc	20	program counter	Y
sp	21	stack pointer	Y
ra	22	return address	N

Instructions

Instruction	Encoding	Arguments (bytes)	Description	Example
nop	0	0	Do nothing
halt	1	0	Halt execution
syscall	2	1	System call handled by user-registered function. Machine specific. Argument is the system call number, allowing up to 256 system calls.	`syscall 42`
lcons	3	4	Store an immediate value in a register. Can also store a variable address.	`lcons r0, 0xA201d800`, `lcons r2, $DataInRam`
mov	4	2	Copy a register in another one.	`mov r0, r2`
push	5	1	Push a register onto the stack.	`push r0`
pop	6	1	Pop the first element of the stack to a register.	`pop r7`
store	7	3	Copy a value from a register to a ram address located in a register with a specified size	`store @r4, r1, 2` ; Copy R1 to address of R4, 2 bytes
load	8	3	Copy a value from a ram address located in a register to a register, with a specific size.	`load r0, @r3, 1` ; 1 byte
add	9	2	sum and store in first reg.	`add r0, r2`
sub	10	2	subtract and store in first reg.	`sub r0, r2`
mul	11	2	multiply and store in first reg .	`mul r0, r2`
div	12	2	divide and store in first reg.	`div r0, r2`
shiftl	13	2	logical shift left.	`shl r0, r1`
shiftr	14	2	logical shift right.	`shr r0, r1`
ishiftr	15	2	arithmetic shift right (for signed values).	`ishr r0, r1`
and	16	2	and two registers and store result in the first one.	`and r0, r1`
or	17	2	or two registers and store result in the first one.	`or r0, r1`
xor	18	2	xor two registers and store result in the first one.	`xor r0, r1`
not	19	1	not a register and store result.	`not r0`
call	20	1	Set register RA to the next instruction and jump to subroutine, must be a label.	`call .media`
ret	21	0	return to the address of last callee (RA).	`ret`
jump	22	1	jump to address (can use label or address).	`jump .my_label`
jumpr	23	1	jump to address contained in a register.	`jumpr t9`
skipz	24	1	skip next instruction if zero.	`skipz r0`
skipnz	25	1	skip next instruction if not zero.	`skipnz r2`

Assembler

Basic grammar

Example:

; ---------------------------- Base node Type: Transition
.mediaEntry0004:
    lcons r0, $fairy
    lcons r1, $la_fee_luminelle
    syscall 1
    lcons r0, .mediaEntry0006
    ret

Global variables