SIC/EM Translator

You shall develop an absolute translator for a subset of the SIC/XE machine instructions described in your course text (BECK). It will use the same machine instruction mnemonics, opcodes, registers, formats, and requirements as described in BECK, except where noted. The subset will be referred to as a SIC/EM machine (SIC Economy Model).

BECK Appendix A is an important reference for machine instructions. Chapter provides further details, such as the numerical designations for the different registers.

Your translator shall read a special language described below, and generate at most a single machine instruction for each statement it reads.

SIC/EM Machine

The SIC/EM machine, as an economy model of the SIC/XE, is missing some of the features of the SIC/XE, but like the SIC/XE, is upward-compatible with the basic SIC machine. Also, SIC/EM programs will run on a SIC/XE machine, as the SIC/EM does not introduce any new features.

The SIC/EM machine lacks a floating-point unit, and so does not have a floating-point register, nor does it handle any of the floating-point instructions specified for the SIC/XE. Also, the SIC/EM does not have a base register, so no base-relative addressing modes are provided. (The "b" bit is always zero in a SIC/EM instruction.) Only direct addressing and PC-relative addressing are understood by the SIC/EM machine. Further, the SIC/EM does not support channel I/O, so those instructions are likewise not supported.

Translator Language

The translator shall read statements until an EOF (end of file) is read. Each statement will be read and then processed. Each statement shall have the following format:

MNEMONIC MODE OPERAND MODIFIER ;COMMENT

Where:
• MNEMONIC - the opcode listed in appendix A; a + preceding the mnemonic indicates Format 4, if applicable
• MODE - one of:
  • - use simple addressing mode
  • @ use indirect addressing mode
  • # use immediate addressing mode
• OPERAND - A decimal numeric value, or a user-defined symbol
• MODIFIER - one of:
  • a ",X" to indicate indexed-mode
  • a ",P" to indicate PC-relative addressing
  Only one of ,X or ,P may be specified, or neither; it is optional.
• ;COMMENT - anything following a semicolon is considered a comment, up to the end of the statement; comments are optional

Symbols and instructions are not case sensitive. (You may cast all input to upper or lower case as you desire.) All symbols begin with a character in A..Z (or a..z), and are followed by up to seven additional characters in A..Z0..9 (or a..z0..9). Symbols longer than eight characters should generate an error. No user-defined symbol may be the same as any instruction or psuedo-operation.

Note that since a ,P (PC-relative addressing) mode is explicitly specified, the assembler does not have to decide whether or not to choose simple addressing over relative addressing. However, it still must check -- if PC-relative addressing is specified, and the specified location is not in the range PC-2048..PC+2047 (PC-x800..PC+x7FF), then an error should occur ("Operand out of range"). This is not the techniqued specified by BECK.

Psuedo-Operations

A number of psuedo-operations, or assembler directives, are defined for this assembler.

• EQU is of the form

  EQU symbol expr

EQU is used to define new symbols. You may not redefine an existing symbol. The expr must be a decimal number or an expression in terms of previously defined symbols. If the expr is a *, then it is taken as the value of the location counter. Note that this has the effect of defining a label.


• START is of the form

  START symbol expr

START must be used exactly once in every program. It must be used before the location counter is ever referenced or altered. The expr must be an expression that is already defined (either a symbol defined with EQU or a decimal number). The effect is to set the initial value of the location counter and to also assign that value to the specified symbol.


• END is of the form

  END expr

END is similiar to BECK's END. The expression must only involve previously-defined quantities.


• BYTE is of the form

  BYTE absexpr

BYTE allocates and initializes a single byte of memory from the provided absolute expression. BECK's X'hh' and C'c' syntax should be supported.


• WORD is of the form

  WORD expr

WORD allocates and initalizes a single word of memory, and expr is an absolute or relocatable expression. For example:

          WORD 63
          WORD ALPHA
          WORD *
    



• RESB is of the form

  RESB absexpr

RESB allocates, but does not initialize, the specified number of bytes of storage. Note that absexpr must be already been defined, or it must be a decimal number. No output records need to be produced, just the location counter advanced.


• RESW is of the form

  RESW absexpr

RESW allocates, but does not initalize, the specified number of bytes of storage. Note that absexpr must already be defined, or it must be a decimal number. No output records need to be produced, just the location counter advanced.

Sample Input

Sample input and output files will be provided.

Input
• Example Input File
• Example Output File