C-Course-Assembler-Project

This project is based on the two-pass assembler model.

Getting Started

The project was coded and compiled using Ubuntu, but it may run on all Linux versions.

Usage

To build the program you can use makefile by make command:

>   make

The assembly files need to be with an .as extension. After compile, you can send the file names to the program as arguments (without the file extensions).

To compile the files x.as, y.as, hello.as you need to run:

>   assembler x y hello

The output files with the same filenames and the following extensions:

• .ob - Object file
• .ent - Entries file
• .ext - Externals file

An example of input and output files can be found under input-output folder.

Instruction

Instruction Structure

Every software instruction is encoded into a few words in memory, The first word is of the following structure:

23 22 21 20 19 18	17 16	15 14 13	12 11	10 9 8	7 6 5 4 3	2 1 0
Opcode	Addressing source	Source	Addressing destination	Destination	Funct	A R E

Commands

Instruction name	funct	Opcode (decimal)
mov		0
cmp		1
add	1	2
sub	2	2
lea		4
clr	1	5
not	2	5
inc	3	5
dec	4	5
jmp	1	9
bne	2	9
jsr	3	9
red		12
prn		13
rts		14
stop		15

Directives

A directive line of the following structure:

1. An optional preceding label. e.g. HELLO: .

2. A directive: .data, .string, .struct, .entry or .extern.

3. Operands according to the type of the directive.

   .data

   Allocates memory in the data, storing received integers later in memory. The parameters of .data are valid integers (separated by a comma).
   E.g: .data 7, –57, +17, 9.

   .string

   Receives a string as an operand and stores it in the data image. (stores char encoded ny their ASCII values). E.g. STR: .string “abcdef”

   .entry

   Received name of a label to the symbol table, for recognize later in other assembly files (and they would be able to use it). E.g.

   ; file1.as
   .entry HELLO 
   HELLO: add #1, r1 
   

   .extern

   Receives a name of a label as a parameter and declares the label as being external (defined in another file).

Registers

There are 8 CPU registers: r0, r1, r2, r3, r4, r5, r6, r7.
The size of each register is 24 bits.

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