9/20/6Lecture 3 - Instruction Set - Al1 Project Description

9/20/6Lecture 3 - Instruction Set - Al2 Semester Project Specification  Will interactive develop the specification and description for the semester simulation project.  Target is the Easy 68K assembler/simulator  Brings into focus and practice the topics discussed so far and many yet to come.

What is the objective  The objective is to write an 68k assembler written in 68K assembler.  Will not be for the full 68K assembler language, but a large subset to start.  Assemblers are 2 pass programs On the first pass lexical analysis is done and symbols are resolved into values. On the second pass, using the resolved symbols, code is generated. 9/20/6Lecture 3 - Instruction Set - Al3

The first step  Develop a dictionary of words and symbols For example: A label starts with a letter and then has up to xxx letters, numerals, and ‘_’s.  LABEL == LETTER {[LETTER|NUMERAL|_]}  LETTER == A|B|C|…  NUMERAL == 1|2|3|4|5|6|7|8|9  RESERVED_WORD == MOVE|ADDA|  As part of the start of the project define a dictionary. 9/20/6Lecture 3 - Instruction Set - Al4

Lexical Analysis  How to start the project  Create a dictionary  STEP 1 of coding Read the input file and be able to write it back out. Will use TRAP 15 to do this D0 has a value which indicates which task to perform. Write a program to output the file you just read in. 9/20/6Lecture 3 - Instruction Set - Al5

Step 1 completed  Should now be able to read input file and mirror it to an output file.  9/20/6Lecture 3 - Instruction Set - Al6

Once text file read in  Start scanning line to find elements in your dictionary  When a character/number/symbol is encountered you move into a decision chart to determine which element of you dictionary you have found 9/20/6Lecture 3 - Instruction Set - Al7

Actions  Scan the line read character by character, i.e., byte by byte  At the start, skip over white space, i.e., blank characters, a hexadecimal 20 until a non space character is found.  Then branch on what character is Build up a decision tree 9/20/6Lecture 3 - Instruction Set - Al8

Next step  Create the state table for identifying know names (in dictionary)  If user defined name find full name and enter into a table  Create a file with “some program in it” to allow development of code to start scanning it.  Scan the line to identify the reserved words and user defined names, special symbols, and numbers  User defined names are entered in a table and they will be linked with a value by the end of the 1 st pass.  Project a due date of about Feb 21.  For reserved words output a code that will be easier to identify on the 2 nd pass when the temp file is read in again. 9/20/6Lecture 3 - Instruction Set - Al9

Instructions to include INSTRUCTIONS Assembler Directives  ADD ORG  AND DC  Bcc DS  BRA END  CLR  CMP  CMPA  JMP  LEA  LSR,LSL  MOVE  MOVEA  NOT  OR  PEA  SUB 9/20/6Lecture 3 - Instruction Set - Al10

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