felsweg / pseudo-asm-javascript

Pseudo Assembler Virtual Machine in Javascript using Ember

Virtual Assembler Interpreter in Javascript (VASM)

This project implements a fictional assembler language interpreter in javascript. The main purpose of this project is to get acquainted with (toy) assembler languages, and the concepts behind it.

Quickstart

Everything is handled and done via make and docker. To install emberjs, call the target:

make install.ember

This will create a new docker image called emberjs in your local docker repository. Next the application needs to be build. Run

make setup

This will install all npm dependencies.

To launch the application just run:

make

This will start ember serve on the code repository. A small message will show on the console, how to access the application via the browsers.

Per default it should be http://localhost:4200

Instruction Set

The following tables give an overview of the instructions, the memory layout, and the registers.

abbreviations

• Register (R)
• Number (N)

OpCode	Description
jmp	unconditional jump
jeq	jump, if FLG register == 0
jne	jump, if FLG register != 0
jez	jump, if FLG register == 0 (?)
jgz	jump, if FLG register > 0
jlz	jump, if FLG register < 0
add R / N
sub R / N
div R / N
mul R / N
mod R / N
mov R, R / N
tst R, R/N	tests, if target and source are the same. modifies FLG
swp	swaps acc and bak
psh	push a value to the stack
pop	pops a value from the stack
nop	no operation
swp R / N	swp acc with bak

Future Opcodes (not implemented yet)

OpCode	Description
shl R / N	shift acc left
shr R / N	shift acc right
xor R / N	(bitwise) xor acc
orr R / N	(bitwise) or acc
and R / N	(bitwise) and acc

Registers

VASM consists of four registers

Register	Description
ACC	A general purpose registers called the accumulator. All operations are done on this register.
BAK	A backup register. Cannot be directly written to, but read from.
FLG	The flag register. The main purpose of this register is to store information on operations done on acc.

Future Registers

Register	Description
(LFT)	Access data from left port
(RGH)	Access data from right port
(TOP)	Access data from top port
(BOT)	Access data from bottom port
(LST)	Access data from last port
(ANY)	Access data from any port, whatever provides data first
(ZER)	A zero registers. This mainly does nothing, when read from it provides a zero

Example Code

The following example code initializes acc with 0 and loops, adding 1 on each iteration, swp the result of acc to bak returning to the beginning of the list of instructions.

begin:              
mov acc, 0          
                    
loop:               
add 1               
cmp acc, 10         
jeq end             
jmp loop            
                    
end:                
swp                 
jmp begin           

Parser Internals

The VASM parsers is technically a LR(1) parser that reads a symbol at a time, looks the next symbol(token), and creates an instruction in form of a javascript function, that will be pushed at the end of the list of instructions. It sucessfully handles labels (jump targets), by pushing the seen label into a temporary stack. If the next token is an instruction, the temporary label stack is being cleared, and the respective label will be stored with the address of that instruction ( which effectively simulates the program counter or "pc"). Since, we simply do not to handle memory addresses directly ( but indeces of the list of instructions), we don't have to calculate the memory offsets all by ourselfes, which makes things quite easy.

TODO

• convert logic into ember component