YourFirstASM

This project was constructed using Flex and Bison. These utilities are
used to make various compilers such as gnu-c, gnu-asm, etc., based on
an input grammer similar to BNF language grammers. The files of most
interest in this project are the files scanner.l (the lexer file) and 
parser.y (the parser grammer). These files are the input to Flex and 
Bison, respectively. 

Here are a short description of each source file:

scanner.l	This file contains a definition for Flex. Flex compiles
		this file into a regular c file (scanner.c) that reads
		input from a file and outputs tokens to the parser. In
		simple terms, it breaks the input file into the various
		identifiers, keywords, numbers, strings, and punctuation.

parser.y	This file contains a BNF-like grammer definition. Bison
		compiles this file into a regular c file (parser.c) that
		takes tokens from the scanner and with the grammer
		syntax parses the input file. The grammer definition is
		embedded with actions that generate the assembler output
		for the given input file.

	** For more information on input scanners and parsers see ***
			Flex and Bison, or Lex and Yacc.

yfasm.h		The yfasm.h contain any definitions that are shared 
		between the lexer and the parser source files.

yfsys.h		Contains information about the CPU design such as bit
		widths of the instruction word and mnemonic op-codes.

scanner.c	These files are generated by Flex and Bison and the
  & parser.c	input files scanner.l and parser.y. Thus these files
  		are not included in the distribution and are also
		deleted by "make clean".

main.c		The main program. Very simple in design it calls the
		parser on each input file. It then takes the assembler
		output (raw instruction memory) and formats it to stdout.


This is the initial construction of an assembler for the Your First CPU
soft processor tutorial. To simplify the code many features were not
included such as a fancy command line parser with switches. 

Currently, the yfasm program assembles all source files on the command
line and outputs a single hex integer per line for each instruction.
This output file format is suitable for ModelSim and many others that
load memory contents via the $readmemh() verilog directive.


To compile the assembler, use:

$  make


To compile the test asm file with the assember, use:

$  ./yfasm test.asm > test.rom


The Makefile also contains some other commands, such as:

make clean	Cleans intermediate object files.

make test	Compiles the assembler and runs it against a test asm
  		input file (test.asm). (note!) Do not redirect this to a 
		rom file, or the assembler build info will be redirected
		as well!

make depend	refreshes the dependancies between the source files. Use
  		this if you adjust the include files or add source files
		to this project.

make rebuild	perform a "make clean" and "make".