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jb302@37: \index Index
jb302@37: \shortcut idx
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jb302@37: \end_index
jb302@37: \secnumdepth 3
jb302@37: \tocdepth 3
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jb302@37: \quotes_language english
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jb302@37: \end_header
jb302@37: 
jb302@37: \begin_body
jb302@37: 
jb302@37: \begin_layout Part
jb302@37: The Assembler
jb302@37: \end_layout
jb302@37: 
jb302@37: \begin_layout Section
jb302@37: Assembler Design
jb302@37: \end_layout
jb302@37: 
jb302@39: \begin_layout Standard
jb302@39: The assembler will take assembly source code as input and produce two output
jb302@42:  files: a binary executable and a debug file.
jb302@39: \end_layout
jb302@39: 
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jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Graphics
jb302@39: 	filename /home/jmz/qm/ede/docs/img/asm/assembler.svg
jb302@39: 	display false
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
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jb302@39: 
jb302@39: 
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jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: The binary executable will be a simple raw binary file in big-endian format.
jb302@39:  The debug file will be a tabulated text file with the following format:
jb302@39: \end_layout
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jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Tabular
jb302@39: <lyxtabular version="3" rows="1" columns="5">
jb302@39: <features tabularvalignment="middle">
jb302@39: <column alignment="center" valignment="top" width="0">
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jb302@39: PC
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jb302@39: DATA
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jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: MNEMONIC
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jb302@39: 
jb302@39: \end_inset
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jb302@39: <cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
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jb302@39: 
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jb302@39: ARGUMENTS
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jb302@39: </lyxtabular>
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jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This file will essentially be the plain text source side by side with the
jb302@39:  binary machine code and address for each instruction (represented as hexadecima
jb302@39: l for greater readability).
jb302@39:  This file will provide the information needed for setting break pointers
jb302@39:  with the debugger later, it will also be generally useful for debugging
jb302@42:  programs written in the assembler, and the assembler itself.
jb302@39: \end_layout
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jb302@39: \begin_layout Standard
jb302@39: \begin_inset Newpage pagebreak
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsection
jb302@39: Language design in BNF syntax
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@42: The ELB816 specification [1] defines an assembly language in Backus Naur
jb302@42:  form, however the assembler designed for this project differs slightly
jb302@42:  (more details in Assembler Implementation below).
jb302@39:  Here is the language definition for this assembler:
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jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <assembly_code> ::= <line> <assembly_code> | <line> <EOF> 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <EOF> ::= <end of file>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <line> ::= [<statement> [";"<comment>]] <EOL>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <EOL> ::= <end of line character>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:   
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <statement> ::= [<label> ":"] <mnemonic> [<arguments>]
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:               | [<label>] <directive> [<arguments>]
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:               | <label> ":"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <character> ::= <any ASCII character>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <mnemonic> ::= "MOV" | "NOP" | "XCSD" | "SFA" | "LAF" | "ANL" 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "ORL" | "XRL" | "RL" | "RLC" | "RR" | "RRC"             
jb302@39:                                                                        
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "INC" | "DEC" | "SET" | "CLR" | "CPL" | "ADD" 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "ADD" | "ADDC" | "SUB" | "SUBB" | "PJUMP"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "PCALL" | "LJMP" | "LCALL" | "DJNZ" | "CJNE"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "RET" | "RETI" | "SJMP" | "JMP" | "JZ" | "JNZ"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "JC" | "JNC" | "JPO" | "JPE" | "JS" | "JNS"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | "PUSH" | "POP" | "IN" | "OUT" | "HLT"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <directive> ::= "ORG" | "EQU" | "DB" | "DS" 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <arguments> ::= <argument> | <arguments> "," <argument>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <argument> ::= <register> | <reg_pair> | ["@"] <address>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:              | <flag> | ["#"] <aggregate>
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <register> ::=  "A" | "FLAGS" | "R0" | "R1" | "R2" | "R3"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:               | "DPH" | "DPL" | "SPH" | "SPL"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <reg_pair> ::= "DPTR" | "SP" | "PC"
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <flag> ::= "C" | "IE" | "BS" 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: <aggregate> ::= ["("] <python arithmetic> [")"] | <python integer>
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@37: \begin_layout Section
jb302@37: Assembler Implementation
jb302@37: \end_layout
jb302@37: 
jb302@39: \begin_layout Standard
jb302@39: The assembler is written in pure Python 2 using only the standard library.
jb302@39:  It assembles the assembly the language described in the ELB816 specification
jb302@42:  [1] with a few minor differences.
jb302@39:  These differences are:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: In-line arithmetic must be wrapped in curved brackets eg.
jb302@39:  start with '(' and end with ')'.
jb302@39:  This is a limitation of the design of the program and to change it would
jb302@39:  require a large amount of code to be re-written.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: The only directives that have been implemented are 
jb302@39: \begin_inset listings
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jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: ORG
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: , 
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jb302@39: lstparams "basicstyle={\ttfamily}"
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jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: EQU
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: , 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: DB
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  and 
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jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: DS
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: .
jb302@39:  The other directives listed in the specification have not been implemented,
jb302@39:  but there omission is only due to time constraints and they could easily
jb302@39:  be implemented in a later version.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: Macros have not been implemented also due to time constraints.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: The assembler consists of two files: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
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jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: language.py
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  which contains the language definition in an index and some functions to
jb302@39:  help encode instructions.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: assembler.py
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  which contains the first and second pass functions and handles opening
jb302@39:  source files and writing binary files.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: The following sections details the design and behavior of the assembler.
jb302@39:  However it must be noted that these are abstract and high level descriptions
jb302@39:  that do not fully explain minor routines, but give an overview of the entire
jb302@39:  process.
jb302@42:  The full commented source code is provided with the Supporting Material
jb302@42:  and should be referenced for a deeper understanding of the program's operation.
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Newpage pagebreak
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsection
jb302@39: Data Structures
jb302@39: \end_layout
jb302@39: 
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jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: reserved arguments
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This structure contains a list of string representations of the reserved
jb302@39:  word arguments for the instruction set.
jb302@39:  These all equate to registers or register pointers.
jb302@39:  The full list is as follows:
jb302@39: \end_layout
jb302@39: 
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jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: a, c, bs, ie, flags, 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: r0, r1, r2, r3, 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: dptr, dpl, dph,  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: sp, sph, spl,
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: @a+pc, @a+dptr, @dptr
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
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jb302@39: \begin_layout Itemize
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jb302@39: status open
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jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: relative instructions
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This structure contains a list of string representations of the mnemonics
jb302@39:  of instructions that use relative addressing.
jb302@39:  The full list is as follows:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily},captionpos=b,frame=tb,framexbottommargin=1em,framextopmargin=1em,keywordstyle={\color{blue}},tabsize=4"
jb302@39: inline false
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: djnz, cjne, sjmp, jz,
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: jnz, jc, jnc, jpo, 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: jpe, js, jns
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: instruction index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This structure contains an index of all possible instructions in the instruction
jb302@39:  set, along with the the corresponding opcode and instruction width.
jb302@39:  This is implemented using a combination of Python's dictionary, tuple and
jb302@39:  list objects.
jb302@39:  Its structure is demonstrated below:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily},captionpos=b,frame=tb,framexbottommargin=1em,framextopmargin=1em,keywordstyle={\color{blue}},tabsize=4"
jb302@39: inline false
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: mnemonic: (arg type, arg type, ...): [opcode, width]
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: Each mnemonic has an entry in the parent index which returns another index
jb302@39:  of possible argument formats for that mnemonic with their corresponding
jb302@39:  opcode and length.
jb302@39:  Argument types can be either be one of the reserved arguments or one of
jb302@39:  the following values: 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: address
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: , 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: pointer
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: , 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: data
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  or 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: label
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  .
jb302@39:  Width is represented in number of bytes, ie.
jb302@39:  
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: width = 3
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  means 1 byte of opcode and 2 bytes of arguments.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: label index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This structure is used to store an index of label definitions.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: equate index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This structure is used to store an index of equated strings.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Newpage newpage
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsection
jb302@39: Functions
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: first_pass(source file)
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This function pre-processes a source file and stores it in a format containing
jb302@39:  the necessary data for the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: second_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  function to assemble it.
jb302@39:  It processes labels and 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: EQU
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  directives by storing strings and their corresponding values in indexes
jb302@39:  and replacing any subsequent appearances of the string with the value.
jb302@39:  It prepares 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: ORG
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  and 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: DB
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  statements for the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: second_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: .
jb302@39:  It uses the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: tokenize()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  function to determine the argument symbols and operand bit string.
jb302@39:  Finally it uses the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: instruction index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  to determine the instruction width.
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: second_pass(asm, label index)
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This function takes the pre-processed assembly code and 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: label index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  output by 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: first_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  as input.
jb302@39:  First it checks for 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: ORG
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  and 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: DB
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  statements and handles them if necessary.
jb302@39:  Then it replaces any labels that were used before they were defined and
jb302@39:  therefore not replaced on by 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: first_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  .
jb302@39:  It uses the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: instruction index 
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  to determine the opcode and the width of the instruction, then it writes
jb302@39:  the opcode and operand to the file.
jb302@39:  If the combined width of the opcode and operand is greater than the instruction
jb302@39:  width the function raises an error.
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: tokenize(mnemonic, arguments)
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This function processes an instruction in order to produce a hashable symbol
jb302@39:  that represents the format of its arguments.
jb302@39:  This symbol is used to look up opcodes in the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: instruction index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: .
jb302@39:  It also detects string representations of numbers in the arguments and
jb302@39:  stores a C type struct representation of the operands to be returned along
jb302@39:  with the symbol.
jb302@39:  It does this with the help of the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: stoi()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  function and Python's 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: struct
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  module .
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Itemize
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: stoi(string)
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: This function is a general purpose function that is actually used throughout
jb302@39:  the code, although mainly in the 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: tokenize()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  function.
jb302@39:  It takes a string as an input and tries to convert it to an integer using
jb302@39:  Pythons integer representation syntax.
jb302@39:  It can recognize decimal, octal, hexadecimal and binary numbers which are
jb302@39:  denoted with different prefixes.
jb302@39:  If it receives a string it can not represent as an integer it returns the
jb302@39:  string 'NaN', (Not a Number)
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset ERT
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 
jb302@39: \backslash
jb302@39: bigskip
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: Below is an abstract representation major components of the assembler.
jb302@39:  The 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: first_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  and 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: second_pass()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  are represented in pseudo-code, 
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\ttfamily}"
jb302@39: inline true
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: tokenize()
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39:  is more easily understood when represented as flowcharts.
jb302@39:  
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Newpage newpage
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsubsection
jb302@39: first_pass
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\small\ttfamily},captionpos=b,frame=tb,framexbottommargin=3em,framextopmargin=3em,keywordstyle={\color{blue}},showstringspaces=false,tabsize=4"
jb302@39: inline false
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: first_pass(source file):
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	address = 0
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	for statement in source file:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		remove comments
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		for word in statement:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			if word is in equate index:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				replace word with equated value
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			else if word is in label index:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				replace word with address at label
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			if first word == 'org'
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				address = second word
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			else if last character of first word == ':':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				remove ':'
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				add word = address to label index
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				next statement
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			else if second word == 'equ'
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				add first word = third word to equate index
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				next statement
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		mnemonic = first word
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		arguments = [second word ...
jb302@39:  last word]
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		symbol, constant = tokenize(arguments)
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		if mnemonic == 'db':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = address + width of constant
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			next statement
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		if mnemonic == 'ds':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = address + first argument
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			next statement
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:         width = instruction index[mnemonic][symbol][width]
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		address = address + width
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		append [mnemonic, argument, symbol, constant] to asm
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	return asm, label index
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \begin_inset Newpage newpage
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsubsection
jb302@39: second_pass
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset listings
jb302@39: lstparams "basicstyle={\small\ttfamily},breaklines=true,captionpos=b,frame=tb,framexbottommargin=3em,framextopmargin=3em,keywordstyle={\color{blue}},tabsize=4"
jb302@39: inline false
jb302@39: status open
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: second_pass(file, asm, label index):
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	address = 0
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	for line in asm:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		file offset = address
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		mnemonic, arguments, symbol, constant = line
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		if mnemonic == 'org':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = first argument
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			next line
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		else if mnemonic == 'db':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			write constant to file
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = address + width of constant
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			next line
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		if mnemonic == 'ds':
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = address + first argument
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39:             next line
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		for argument in arguments:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			if argument is a label:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				replace argument with address at label
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				symbol, data = tokenize(argument)
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 				append data to constant
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		op, width = instruction index[mnemonic][symbol]
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		write op to file
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		if width of constant - width + 1 > 0:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			raise error
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 		else if:
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			write constant to file
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 			address = address.+ width
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Plain Layout
jb302@39: 
jb302@39: 	return file
jb302@39: \end_layout
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Newpage pagebreak
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Subsubsection
jb302@39: tokenize
jb302@39: \end_layout
jb302@39: 
jb302@39: \begin_layout Standard
jb302@39: \begin_inset Graphics
jb302@39: 	filename /home/jmz/qm/ede/docs/img/asm/tokenize.svg
jb302@39: 	display false
jb302@39: 
jb302@39: \end_inset
jb302@39: 
jb302@39: 
jb302@39: \end_layout
jb302@39: 
jb302@37: \begin_layout Section
jb302@37: Assembler Testing
jb302@37: \end_layout
jb302@37: 
jb302@41: \begin_layout Standard
jb302@41: The assembler was tested by assembling the entire instruction table, while
jb302@41:  at the same time testing labels and directives.
jb302@41:  The test file was assembled and then the binary and .dsm files were inspected
jb302@41:  manually by checking their size and content.
jb302@42:  None of this testing is automated and files are inspected by hand.
jb302@42:  The test files and results can be found in the Supporting Material.
jb302@41: \end_layout
jb302@41: 
jb302@37: \end_body
jb302@37: \end_document