Setting up Codio for this HW:

1) Open the Codio assignment via Canvas

2) From the Codio File-Tree click on: assembler.c

NOTE:

If your program is crashing, before you can be helped via TA office hours, you must run GDB on your program. A small amount of detective work with GDB will save hours! Be prepared for  TAs to tell you to run GDB before they will help you in office hours. Watch the tutorial and run it on

your program if it is crashing!

Assignment Overview:

From lecture you!ve learned that C is file-oriented and that working with files represents I/O devices in C. C places files into two categories: "text” and "binary.” In this assignment you!ll        work with both types by reading in a text file and writing out a binary file. The text file that you will read in this assignment will be a .ASM file (a text file intended for PennSim) and the type of output file you!ll generate will be a .OBJ file ( the same type of binary file that PennSim would   write out) . Aside from reading and writing out the files, your task will be make a mini- LC4- Assembler! A program that reads in assembly language and generates its machine equivalent.  This assignment will require a bit more programming rigor than we!ve had thus far, but now      that you!ve gained a good amount of programming skill in this class and in others, it is the          perfect time to tackle a large programming assignment.

Problem #1: Reading in a text file (the .ASM file)

Open "assembler.c” from the helper files; it contains the main() function for the program. Carefully examine the variables at the top:

char* filename = NULL ;

char program [ROWS][COLS] ;

char program_bin_str [ROWS][17] ;

unsigned short int program_bin [ROWS] ;

The first pointer variable "filename” will be a pointer to a string that contains the text file you!ll be reading. Your program must take in as an argument the name of a .ASM file. As an  example, once you compile your main() program, you would execute it as follows:

./assembler test.asm

In your last HW you learned how to use the arguments passed into main(). So the first thing to implement is to check if argc has arguments, and if it does, point "filename” to the argument    that contains the passed in string that is the file !s name. You should return from main() immediately (with an error message) if the caller doesn!t provide an input file name as follows:

error1: usage: ./assembler 

Start by updating "assembler.c” to read in the arguments. Compile your changes and test them before continuing. You should take this moment to setup your Makefile as well, it should contain two basic directives: assembler and asm_parser.o

After you!ve successfully gotten the filename from the caller, the first function you must call will be:

int read_asm_file (char* filename, char program [ROWS][COLS] ) ; The purpose of read_asm_file() is to open the ASM file, and place its contents into the 2D array: program[][]. You must complete the implementation of this function in the provided helper  file: "asm_parser.c” . Notice, it takes in the pointer to the "filename” that you!ll open in this                  function. It also takes in the two dimensional array, program, that was defined back in main().    You!ll see that "ROWS” and "COLS” are two #define!ed constants in the file: asm_parser.h.  Rows is set to 100 and COLS is set to 255. This means that you can only read in a program that  is up    to 100 lines long and each line of this program can be no longer than 255.

You!ll want to look at the class notes (or a C-reference textbook) to use fopen() to open the   filename that has been passed in. Then you!ll want to use a function like: fgets() to read each line of the .ASM file into the program[][] 2D array. Be aware that "fgets()” will keep carriage  returns (aka – the newline character) and you!ll need to strip these from the input.

Take a look at test.asm file that was included in the helper file. It contains the following

program:

ADD R1, R0, R1

MUL R2, R1, R1

SUB R3, R2, R1

DIV R1, R3, R2

AND R1, R2, R3

OR R1, R3, R2

XOR R1, R3, R2

After you complete read_asm_file() and if you were to run it on test.asm, your 2D array: program[][]should contain the contents of the ASM file in this order:

Notice, there are no "newline” characters at the end of the lines.

If reading in the file is a success, return 0 from the function, if not, return 2 from the function

and print an error to the screen: error2: read_asm_file() failed     Implement and test this function carefully before continuing on with the assignment.

Problem #2: Parsing an Instruction

Once read_asm_file() is working properly, back in main(), you!ll call the function:

parse_instruction(), which is also located in asm_file.c:

int parse_instruction (char* instr, char* instr_bin_str) ;

NOTE: You are required to implement the following instructions:

ADD, MUL, SUB, DIV, AND, OR, XOR

(ADD IMMEDIATE and AND IMMEDIATE are not required

but will be EC, as detailed on page 10)

purpose, arguments & return value

The purpose of this function is to take in a single row of your program[][] array and convert to its binary equivalent – in text form. The argument: instr must point to a row in main()!s 2D       array: program[][]. The argument: instr_bin_str must point to the corresponding row in            main()!s 2D array: program_bin_str[][] . If there no errors are encountered the function will      return a 0 and if any error occurs (in this function) it should return the number 3 and an error message should be printed: error3: parse_instruction() failed.

Let!s assume you!ve called parse_instruction() and "instr” points to the first row in your program[][] array:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Parse_instruction() needs to examine this string and convert it into a binary equivalent. You!ll need to use the LC4 ISA to determine the binary equivalent of an instruction. When your         function returns, the memory pointed to by: instr_bin_str, should look like this:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Notice, this isn!t actually binary, but it is the "ADD” instruction!s binary equivalent in TEXT form. We will convert this string form of the binary instruction to HEX later in the function:                    convert_instrunction().

How to implement this function

The purpose of converting the instruction to a binary string (instead of to the binary # it will eventually become), is so that you can build this string up little by little. Investigate the        "strtok()” function in the standard C string library:

https://www.tutorialspoint.com/c_standard_library/c_function_strtok.htm

STRTOK() allows you to parse a string that is separated by "tokens” . In this function you!ll be    parsing the string pointed to be "instr” and you!ll be building up the string pointed to by            "instr_bin_str” . "instr” will contain spaces and commas (those will be your tokens). Your first   call to strtok() on the "instr” string should return back the OPCODE: ADD, SUB, MUL, DIV, XOR, etc. The only thing common to all 26 instructions in the ISA is that the very first part of them is the opcode. Once you determine the OPCODE, you!ll call the appropriate helper function to     parse the remainder of the instruction.

As an example, let!s say the OPCODE is ADD. For this problem, you do not need to worry about  the "immediate” variants of the ADD instruction (or AND immediate) – when we test your code, we won!t use ADD – immediate or AND immediate instructions. Once you!ve determined the     OPCODE is ADD, you would call the parse_add() helper function. It will take the instruction         (instr) as an argument, but also the instr_bin_str string because parse_add will be responsible    for determining the binary equivalent