annotate doc/general/ede.lyx~ @ 32:b4a4ae2f127e

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\begin_body

\begin_layout Title
EDE: ELB816 Development Environment
\end_layout

\begin_layout Author
James Bowden (110104485)
\end_layout

\begin_layout Abstract
The ELB816 Development Environment consists of an assembler, emulator and
 debugger for the ELB816 microprocessor system.
 This report details the design and usage of each of its elements.
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Standard
\begin_inset CommandInset toc
LatexCommand tableofcontents

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Part
Introduction and Specification
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

\end_inset


\end_layout

\begin_layout Section
Motivations
\end_layout

\begin_layout Standard
The ELB816 architecture is designed to be a 
\begin_inset Quotes eld
\end_inset

simple to understand 8-bit microprocessor system to help learn about microproces
sor electronics.
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The combination of an ELB816 emulator, debugger and assembler could be used
 as a set of tools for learning or teaching microprocessor programming without
 the intricacies of real-world commercial microprocessors getting in the
 way of a fundamental understanding of the subject.
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

\end_inset


\end_layout

\begin_layout Standard
A PC based emulator would allow students to quickly develop and debug programs
 written in a simple assembly language on any modern desktop or laptop and
 an MCS-51 port running on an 8052 would allow students to test programs
 in an actual circuit.
\end_layout

\begin_layout Section
Project Aims
\end_layout

\begin_layout Itemize
Develop an assembler for the ELB816 assembly language.
\end_layout

\begin_layout Itemize
Develop an emulated programmable microprocessor system based on the ELB816
 architecture.
\end_layout

\begin_layout Itemize
Develop a debugger that allows interactive debugging of programs running
 on the emulator.
\end_layout

\begin_layout Section
Methodology
\end_layout

\begin_layout Subsection
Assembler
\end_layout

\begin_layout Description
Language: Python
\end_layout

\begin_layout Description
Priority: First
\end_layout

\begin_layout Standard
The assembler will be developed before anything else so that it can subsequently
 be used to assemble test programs during development of the emulator.
 
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Subsection
Emulator
\end_layout

\begin_layout Description
Language: C
\end_layout

\begin_layout Description
Priority: Second
\end_layout

\begin_layout Standard
The emulator will use only standard libraries in order to ensure it is portable
 between compilers and platforms.
 Specifically GCC for x86 and Keil C51 for Intel MCS-51.
 The emulator will first be developed on Linux to facilitated rapid development.
 It will be ported to MCS-51 once it is complete
\end_layout

\begin_layout Subsection
Debugger
\end_layout

\begin_layout Description
Language: C/Python
\end_layout

\begin_layout Description
Priority: Second
\end_layout

\begin_layout Standard
The debug interface will be developed along side the emulator.
 It will consist of a simple text based interface built into the emulator
 that will read commands using C's 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

stdio.h
\end_layout

\end_inset

 library.
 This means that on Linux the commands will be issued using 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

STDIN
\end_layout

\end_inset

 and on the MCS-51 version they will be issued over a serial interface.
 Python will be used to provide a cleaner interface for common debug procedures
 such as writing programs to memory and setting break-points.
 
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The remainder of this report is split into three parts, one for each component
 of the project, and will attempt to demonstrate the design and usage of
 each of these components.
 
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Part
Assembler
\end_layout

\begin_layout Standard
The assembler is written in pure Python 2 using only the standard library.
 It assembles the assembly the language described in the ELB816 specification
 with a few minor differences.
 These differences are:
\end_layout

\begin_layout Itemize
In-line arithmetic must be wrapped in curved brackets eg.
 start with '(' and end with ')'.
 This is a limitation of the design of the program and to change it would
 require a large amount of code to be re-written.
\end_layout

\begin_layout Itemize
The only directives that have been implemented are 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

ORG
\end_layout

\end_inset

, 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

EQU
\end_layout

\end_inset

, 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

DB
\end_layout

\end_inset

 and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

DS
\end_layout

\end_inset

.
 The other directives listed in the specification have not been implemented,
 but there omission is only due to time constraints and they could easily
 be implemented in a later version.
\end_layout

\begin_layout Itemize
Macros have not been implemented also due to time constraints.
\end_layout

\begin_layout Standard
The assembler consists of two files: 
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

language.py
\end_layout

\end_inset

 which contains the language definition in an index and some functions to
 help encode instructions.
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

assembler.py
\end_layout

\end_inset

 which contains the first and second pass functions and handles opening
 source files and writing binary files.
\end_layout

\begin_layout Standard
The following sections details the design and behavior of the assembler.
 However it must be noted that these are abstract and high level descriptions
 that do not fully explain minor routines, but give an overview of the entire
 process.
 The full source code is attached in the Appendix and should be referenced
 for a deeper understanding of the program's operation.
 The final section is a short programmers manual demonstrating the assembler's
 features.
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Section
Data Structures
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

reserved arguments
\end_layout

\end_inset


\end_layout

\begin_layout Standard
This structure contains a list of string representations of the reserved
 word arguments for the instruction set.
 These all equate to registers or register pointers.
 The full list is as follows:
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "basicstyle={\ttfamily},captionpos=b,frame=tb,framexbottommargin=1em,framextopmargin=1em,keywordstyle={\color{blue}},tabsize=4"
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\begin_layout Plain Layout

a, c, bs, ie, flags, 
\end_layout

\begin_layout Plain Layout

r0, r1, r2, r3, 
\end_layout

\begin_layout Plain Layout

dptr, dpl, dph,  
\end_layout

\begin_layout Plain Layout

sp, sph, spl,
\end_layout

\begin_layout Plain Layout

@a+pc, @a+dptr, @dptr
\end_layout

\end_inset


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lstparams "basicstyle={\ttfamily}"
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\begin_layout Plain Layout

relative instructions
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This structure contains a list of string representations of the mnemonics
 of instructions that use relative addressing.
 The full list is as follows:
\end_layout

\begin_layout Standard
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djnz, cjne, sjmp, jz,
\end_layout

\begin_layout Plain Layout

jnz, jc, jnc, jpo, 
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jpe, js, jns
\end_layout

\end_inset


\end_layout

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\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
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\begin_layout Plain Layout

instruction index
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This structure contains an index of all possible instructions in the instruction
 set, along with the the corresponding opcode and instruction width.
 This is implemented using a combination of Python's dictionary, tuple and
 list objects.
 Its structure is demonstrated below:
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "basicstyle={\ttfamily},captionpos=b,frame=tb,framexbottommargin=1em,framextopmargin=1em,keywordstyle={\color{blue}},tabsize=4"
inline false
status open

\begin_layout Plain Layout

mnemonic: (arg type, arg type, ...): [opcode, width]
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Each mnemonic has an entry in the parent index which returns another index
 of possible argument formats for that mnemonic with their corresponding
 opcode and length.
 Argument types can be either be one of the reserved arguments or one of
 the following values: 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

address
\end_layout

\end_inset

, 
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lstparams "basicstyle={\ttfamily}"
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\begin_layout Plain Layout

pointer
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\end_inset

, 
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lstparams "basicstyle={\ttfamily}"
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data
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\end_inset

 or 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
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\begin_layout Plain Layout

label
\end_layout

\end_inset

 .
 Width is represented in number of bytes, ie.
 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

width = 3
\end_layout

\end_inset

 means 1 byte of opcode and 2 bytes of arguments.
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

label index
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This structure is used to store an index of label definitions.
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

equate index
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This structure is used to store an index of equated strings.
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Section
Functions
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

first_pass(source file)
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This function pre-processes a source file and stores it in a format containing
 the necessary data for the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

second_pass()
\end_layout

\end_inset

 function to assemble it.
 It processes labels and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

EQU
\end_layout

\end_inset

 directives by storing strings and their corresponding values in indexes
 and replacing any subsequent appearances of the string with the value.
 It prepares 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

ORG
\end_layout

\end_inset

 and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

DB
\end_layout

\end_inset

 statements for the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

second_pass()
\end_layout

\end_inset

.
 It uses the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

tokenize()
\end_layout

\end_inset

 function to determine the argument symbols and operand bit string.
 Finally it uses the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

instruction index
\end_layout

\end_inset

 to determine the instruction width.
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

second_pass(asm, label index)
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This function takes the pre-processed assembly code and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

label index
\end_layout

\end_inset

 output by 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

first_pass()
\end_layout

\end_inset

 as input.
 First it checks for 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

ORG
\end_layout

\end_inset

 and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

DB
\end_layout

\end_inset

 statements and handles them if necessary.
 Then it replaces any labels that were used before they were defined and
 therefore not replaced on by 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

first_pass()
\end_layout

\end_inset

 .
 It uses the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

instruction index 
\end_layout

\end_inset

 to determine the opcode and the width of the instruction, then it writes
 the opcode and operand to the file.
 If the combined width of the opcode and operand is greater than the instruction
 width the function raises an error.
 
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

tokenize(mnemonic, arguments)
\end_layout

\end_inset


\end_layout

\begin_layout Standard
This function processes an instruction in order to produce a hashable symbol
 that represents the format of its arguments.
 This symbol is used to look up opcodes in the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

instruction index
\end_layout

\end_inset

.
 It also detects string representations of numbers in the arguments and
 stores a C type struct representation of the operands to be returned along
 with the symbol.
 It does this with the help of the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

stoi()
\end_layout

\end_inset

 function and Python's 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

struct
\end_layout

\end_inset

 module .
\end_layout

\begin_layout Itemize
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

stoi(string)
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
This function is a general purpose function that is actually used throughout
 the code, although mainly in the 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

tokenize()
\end_layout

\end_inset

 function.
 It takes a string as an input and tries to convert it to an integer using
 Pythons integer representation syntax.
 It can recognize decimal, octal, hexadecimal and binary numbers which are
 denoted with different prefixes.
 If it receives a string it can not represent as an integer it returns the
 string 'NaN', (Not a Number)
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Below is an abstract representation of each functions logical process.
 The 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

first_pass()
\end_layout

\end_inset

 and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

second_pass()
\end_layout

\end_inset

 are represented in pseudo-code, however 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

stoi()
\end_layout

\end_inset

 and 
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

tokenize()
\end_layout

\end_inset

 are more easily understood when represented as flowcharts.
 
\end_layout

\begin_layout Standard
\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Subsection
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

first_pass
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "basicstyle={\small\ttfamily},captionpos=b,frame=tb,framexbottommargin=3em,framextopmargin=3em,keywordstyle={\color{blue}},language=Python,showstringspaces=false,tabsize=4"
inline false
status open

\begin_layout Plain Layout

first_pass(source file):
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

	address = 0
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

	for statement in source file:
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

		remove comments
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		for word in statement:
\end_layout

\begin_layout Plain Layout

		
\end_layout

\begin_layout Plain Layout

			if word is in equate index:
\end_layout

\begin_layout Plain Layout

				replace word with equated value
\end_layout

\begin_layout Plain Layout

			else if word is in label index:
\end_layout

\begin_layout Plain Layout

				replace word with address at label
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

			if first word == 'org'
\end_layout

\begin_layout Plain Layout

				address = second word
\end_layout

\begin_layout Plain Layout

			else if last character of first word == ':':
\end_layout

\begin_layout Plain Layout

				remove ':'
\end_layout

\begin_layout Plain Layout

				add word = address to label index
\end_layout

\begin_layout Plain Layout

				next statement
\end_layout

\begin_layout Plain Layout

			else if second word == 'equ'
\end_layout

\begin_layout Plain Layout

				add first word = third word to equate index
\end_layout

\begin_layout Plain Layout

				next statement
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		mnemonic = first word
\end_layout

\begin_layout Plain Layout

		arguments = [second word ...
 last word]
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		symbol, constant = tokenize(arguments)
\end_layout

\begin_layout Plain Layout

		if mnemonic == 'db':
\end_layout

\begin_layout Plain Layout

			address = address + width of constant
\end_layout

\begin_layout Plain Layout

			next statement
\end_layout

\begin_layout Plain Layout

		
\end_layout

\begin_layout Plain Layout

        width = instruction index[mnemonic][symbol][width]
\end_layout

\begin_layout Plain Layout

		address = address + width
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		append [mnemonic, argument, symbol, constant] to asm
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

	return asm, label index
\end_layout

\end_inset


\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Subsection
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

second_pass
\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
\begin_inset listings
lstparams "basicstyle={\small\ttfamily},breaklines=true,captionpos=b,frame=tb,framexbottommargin=3em,framextopmargin=3em,keywordstyle={\color{blue}},language=Python,tabsize=4"
inline false
status open

\begin_layout Plain Layout

second_pass(file, asm, label index):
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

	address = 0
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

	for line in asm:
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

		file offset = address
\end_layout

\begin_layout Plain Layout

		
\end_layout

\begin_layout Plain Layout

		mnemonic, arguments, symbol, constant = line
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		if mnemonic == 'org':
\end_layout

\begin_layout Plain Layout

			address = first argument
\end_layout

\begin_layout Plain Layout

			next line
\end_layout

\begin_layout Plain Layout

		else if mnemonic == 'db':
\end_layout

\begin_layout Plain Layout

			write constant to file
\end_layout

\begin_layout Plain Layout

			address = address + width of constant
\end_layout

\begin_layout Plain Layout

			next line
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		for argument in arguments:
\end_layout

\begin_layout Plain Layout

			if argument is a label:
\end_layout

\begin_layout Plain Layout

				replace argument with address at label
\end_layout

\begin_layout Plain Layout

				symbol, data = tokenize(argument)
\end_layout

\begin_layout Plain Layout

				append data to constant
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		op, width = instruction index[mnemonic][symbol]
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

		write op to file
\end_layout

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout

		if width of constant - width + 1 > 0:
\end_layout

\begin_layout Plain Layout

			raise error
\end_layout

\begin_layout Plain Layout

		else if:
\end_layout

\begin_layout Plain Layout

			write constant to file
\end_layout

\begin_layout Plain Layout

			address = address.+ width
\end_layout

\begin_layout Plain Layout

	
\end_layout

\begin_layout Plain Layout

	return file
\end_layout

\end_inset


\begin_inset Newpage newpage
\end_inset


\end_layout

\begin_layout Subsection
\begin_inset listings
lstparams "basicstyle={\ttfamily}"
inline true
status open

\begin_layout Plain Layout

tokenize
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout


\backslash
bigskip
\end_layout

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stoi
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\begin_layout Description
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\begin_layout Section
Assembly language manual
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\begin_layout Part
Emulator
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\begin_layout Section
Core microprocessor emulation
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The core of the emulator is written in C using only standard libraries.
 It executes the machine code output by the assembler according to the ELB816
 specification.
 It consists of the following files:
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iset.c
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iset.h
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These files contain the emulator instruction functions and function look-up
 table.
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mem.c
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mem.h
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These files contain the emulators memory structure and memory access functions.
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emu.c
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This file contains the program's 
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main()
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 function.
 It initializes the emulator and executes the programs fetch/decode/execute
 cycle.
 
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Below is a high level description of the content of each of these files
 which should demonstrate how the emulator works.
 There is also a large amount of material relevant to the emulator's design
 in the appendix, which will be referenced when applicable.
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iset.c
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Each mnemonic in the ELB816 instruction set has a function defined in these
 files.
 Each function is responsible for execution of all the instructions that
 use its corresponding mnemonic.
 The function look-up table is an array of pointers to these functions,
 where a pointer's position in the list corresponds to the opcode of the
 instruction to be executed.
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mem.c
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mem.h
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The figures bellow illustrate the emulator's memory layout as defined in
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mem.h
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 header file.
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 contains functions that can be used to access this memory from the rest
 of the code.
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emu.c
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\begin_layout Standard
This file contains the emulator's set-up and control procedures.
 It includes all of the projects header files and controls the execution
 of the functions contained in them.
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It first executes a number of initialization procedures and then passes
 control over to the main fetch/decode/execute cycle.
 This procedure is shown below as a flowchart.
 To understand this it you must be familiar with C's function pointer syntax.
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\begin_layout Section
Peripherals
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