Computer Architecture Project 1: Building Assembler ✓ Solved

Computer Architecture Project 1 Building Assembler

Computer architecture is made up of two main components: the Instruction Set Architecture (ISA) and the RTL model for the CPU. In this class, we will have two software projects that will help in your understanding of the ISA and RTL model for the CPU. The first project is the creation of an assembler.

The assembler will be used for you to write assembly language programs that will be executed on the CPU you will design in project #2. The CPU we will be using is based on the DLX design. What is an assembler? All computer software goes through a set of applications to create an executable file that can be used by the end user. The first program a programmer will use is a high-level language program (C, C++, etc.).

The programmer writes in a very high-level abstract environment, writing code such as: For(x=0; x The high-level language allows the programmer to write his program without knowing how the ISA and hardware architecture functions. The language hides all the hardware from the programmer. At some point, the source code needs to be transferred to a language that takes into account the ISA and hardware architecture. The compiler is the next step in the development process. The compiler will take in high-level source code and translate the program into assembly language.

Assembly language is the ISA for a computer. Assembly is the instructions that the computer can perform. The compiler will convert C language to Assembly as follows: c = a + b; becomes load r1, a; load r2, b; add r3, r1, r2; store r3, c; The last part of the development process is taking the assembly code created by the compiler and converting it into machine code that the computer will execute. A computer cannot run written language such as ADD r1,r2,r3;. It runs a program by reading data stored in memory, which contains machine code — the binary representation of an assembly language instruction.

All the information for the DLX machine code and assembly instructions can be found in the handouts given in class. Each of the DLX instruction is 32-bits in length and broken down into three types: R-type, I-type, and J-type.

An example of the R-type instruction is ADD rd, rs1, rs2, with the breakdown of bits as follows: Bits 31-26 is the opcode, Bits 25-21 is rs1, Bits 20-16 is rs2, Bits 15-11 is rd, and Bits 10-0 is the funct. The funct tells what type of ALU operation is being conducted. An example of the I-type instruction is ADDI rs1,rs2,immm, which has bits assigned similarly to the R-type instruction. The J-type instruction example, J address, focuses on the jump operation.

Your Assignment

Project #1 Part 1: This part is not graded but will help you understand the programming aspects you'll need. To get started on creating your assembler, you must enable the program to understand the basic syntax of a text file containing a program. The following items must be completed for part 1:

1. You will need to read in arguments passed from the command line.
2. You will need to parse a string.
3. You will need to convert all letters to lowercase.
4. You will need to compare a string to a list of known words (add, load, store, r0, r1, r).
5. You will need to convert numbers in text to integers in the C program.
6. You will also need to read and write files.

Project #2 Part 2: Your assignment is to create a simple assembler for the DLX processor, using the core instructions only (excluding floating-point instructions). Register names will be r0 to r31, and the assembly source code will hard code any constants and memory locations. You will use labels for branching and jumping in code. For part 2, you must submit a report detailing how you created your program, the source code, test files, and a flow chart.

It is common to run an assembler in a two-pass structure. The first pass goes through the source files and finds all labels and addresses for each instruction, starting the first line of code at memory location 0. You will create a table for labels and addresses. On the second pass, you will convert the assembly instructions into machine code and fill in any labels using your table.

Paper For Above Instructions

The assembler is a crucial component in bridging high-level programming languages and machine code. It translates human-readable assembly instructions into the binary format that a CPU can execute directly. Below is a comprehensive approach to building an assembler for the DLX processor, which adheres to the specifications and requirements outlined in the project instructions.

Part 1: Basic Syntax Understanding

The first part of the project focuses on the fundamental aspects of string processing and file handling. The assembler must be able to read input and output files specified via command line arguments. To accomplish this, the argc and argv arguments in C can be utilized to capture these inputs effectively. Parsing strings using the strtok() function allows the assembler to split the input lines into meaningful tokens, representative of the instructions and operands.

In addition, converting all letters to lowercase helps maintain consistency in instruction recognition, enabling accurate comparisons against a predefined set of valid instructions, such as add, load, store, and register identifiers like r0, r1, etc. The assembler must also convert string representations of numbers into integers, which can be done using the atoi() function in C.

File Input and Output

File handling is another crucial aspect of this initial phase. The assembler needs to be able to read from an input file and write output to a specified output file. Utilizing the C standard library functions such as fopen(), fgets(), and fprintf() will facilitate these operations smoothly. Each line of the input file is processed individually, and all relevant information is extracted from the instructions.

Part 2: Assembler Implementation

For the second part of the project, a simple assembler for the DLX processor will be constructed, focusing solely on core instructions without floating-point operations. The assembler will read the simplified assembly language code, processing it in two distinct passes:

First Pass: Label and Address Table Creation

During the first pass, the assembler will analyze each line of the assembly code to identify labels and instructions. Labels, which are defined by a unique identifier followed by a colon (e.g., loop:), will be stored in a label table along with their respective memory addresses. By starting the first instruction at memory address 0, subsequent instructions are assigned incremental memory locations based on their position in the source code.

Second Pass: Code Translation

In the second pass, the assembler will convert valid assembly instructions into their corresponding machine code representations. This involves looking up the opcode for each assembly instruction based on the DLX instruction set specification and utilizing the label table to resolve any labels in branch or jump instructions. Additionally, instructions will be translated into their binary format, ensuring that each instruction is precisely 32 bits long, with the appropriate fields populated according to the instruction type (R-type, I-type, J-type).

Conclusion

The assembler serves as a fundamental tool in the software development process, enabling programmers to write in a more understandable and manageable form. By completing this project, students will gain hands-on experience with the syntax, structure, and functionality of an assembler, paving the way for a deeper understanding of computer architecture and the interaction between hardware and software.

References

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