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Home Hardware Developing an Intel 8080 CPU Assembler with D: Step-by-Step Guide

Developing an Intel 8080 CPU Assembler with D: Step-by-Step Guide

Updated on Mar 30,2024

Developing an Intel 8080 CPU Assembler with D: Step-by-Step Guide

Table of Contents

  1. Introduction
  2. Writing the Parser
    1. Detecting Labels
    2. Processing Instructions
    3. Handling Arguments
    4. Error Handling
  3. Conclusion

Writing the Parser

In this part of the Tutorial, we will focus on writing the parser for our assembly language. While it may seem like a daunting task, it is actually quite straightforward. The parser's main goal is to process the different tokens that can exist in a line of assembly code, including labels, instructions, and arguments.

Detecting Labels

The first step in the parsing process is to detect labels. Labels are used to mark specific memory locations in the program. To detect a label, we can check if the first character of a line is not a space or a tab. If this condition is true, we know that we have a label. We can then store the label's end position in a variable called end_label using a for loop. If we encounter a colon character or any other end of token character, we can set end_label to the current position in the line. We can use the slice function in D to extract the label from the line. If the label ends with a colon, we can skip the colon character and move on to the next token.

Processing Instructions

Once we have detected the label, we can move on to processing instructions. Instructions are the actual commands that the computer will execute. To process an instruction, we can start at the position where the label ends and iterate through the line until we encounter the end of the token. Once we reach the end of the token, we can use the slice function again to extract the instruction from the line.

Handling Arguments

After processing the instruction, we can move on to handling arguments. Arguments provide additional information to the instruction. We don't know the number of arguments in advance, so we need to handle both cases where there is one argument or two arguments. We can start at the position where the instruction ends and iterate through the line to find the end of the first argument. If the line contains a comma, we know that there is a Second argument. We can extract the first argument using the slice function.

If there is a comma, we can skip it and find the start of the second argument. We can then iterate through the line again to find the end of the second argument. Once we have both arguments, we can use the slice function to extract them from the line.

Error Handling

In case there are extra tokens in the line, we need to handle error cases. If there are more tokens than expected, we can raise an exception and display an error message indicating that extra tokens were found. This will help us identify any syntax errors in our assembly code.

Conclusion

In this part of the tutorial, we have learned how to write a parser for our assembly language. We have covered the process of detecting labels, processing instructions, handling arguments, and error handling. With this parser, we can now successfully parse any line of assembly code. However, there are still some extra niceties that we can add to our assembler, such as allowing spaces before commas in argument separation. This can be done as a Homework assignment for further skill development.

Now that we have completed the parser, we can move on to the next part of the tutorial.

⭐ Highlights:

  • Writing a parser for assembly language
  • Detecting labels, processing instructions, and handling arguments
  • Error handling for syntax errors
  • Additional features as homework

⭐ FAQ

Q: What is the purpose of a label in assembly language? A: Labels are used to mark specific memory locations in the program, allowing easier navigation and referencing.

Q: How are instructions processed in the parser? A: Instructions are obtained by iterating through the line after the label and extracting the instruction token.

Q: How are arguments handled in the parser? A: The parser checks for the presence of a comma to determine if there are two arguments. It then extracts the arguments using the slice function.

Q: What happens if there are extra tokens in the line? A: If there are more tokens than expected, an exception is raised, and an error message is displayed.

Q: Are there any extra features that can be added to the assembler? A: Yes, there are additional niceties that can be implemented, such as allowing spaces before commas in argument separation.

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