asm
This commit is contained in:
Sven Riwoldt
192
asm/asm01.py
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192
asm/asm01.py
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"""Assembler for the hack computer
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Usage:
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python assembler.py file
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Loads an assembly file and translate it into machine language for the hack
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computer as specified in project 6 of the nand2tetris course.
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# Assembler implementation details
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This assembler works in 3 steps:
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1. Load and clean the assembly file
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2. Construct a symbol table referencing the user-defined labels and variables
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3. Translate the asm file to binary code
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The file follows this pattern:
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File parsing (line 147)
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Symbol table (line 207)
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Assembling (line 322)
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??
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# Assembly language specifications:
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## Note on registers
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The Hack computer has three 16-bit registers: the D-, A- and M-registers.
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The D-register is used to store "data" that can be used as input for the ALU.
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The A-register can be used in the same way but it also has a second role:
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The RAM use it as address input. So any read/write instruction to the RAM is
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done on the register which has the value of the A-register as address.
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The M-register represents this register in the RAM that is 'pointed' onto by the
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A-register. Reading/writing to it consists actually in reading/writing to
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the RAM.
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## Assembly instructions
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There are three types of assembly instructions: A-instructions, C-instructions
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and labels. Indents and blanks are ignored. Comments can only be in-line, start
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with "//" and are ignored.
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## A-instructions
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- `"@" integer` where integer is a number in the range 0->32768. Sets the A
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register to contain the specified integer. Ex: @42
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- `"@" label` where label is a user-defined label. Sets the A register to
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contain the code address corresponding to the label.
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Labels are upper-cased by convention, with "_" as word separator. Ex: @MAIN
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- `"@" variable` where variable is a user-defined variable. Sets the A register
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to contain the RAM adress corresponding to the variable. If a variable is
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encountered for the first time, it is automatically assigned an address.
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The address assignment starts at RAM address 16 and increments.
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Variables are lowercased by convention, with "_" as word separator. Ex: @i
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## C-instructions
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`(Dest-code "=")? op-code (";" jump-code)?`
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- op-code:
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Only the op-code is mandatory. It represents an instruction to be performed
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by the ALU. Available codes and their associated outputs are:
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- 0 -> the constant 0
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- 1 -> the constant 1
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- -1 -> the constant -1
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- D -> the value contained in the D-register
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- A -> the value contained in the A-register
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- M -> the value contained in the M-Register
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- !D -> bit-wise negation of the D-register
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- !A -> bit-wise negation of the A-register
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- !M -> bit-wise negation of the M-register
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- -D -> numerical negation of the D-register using 2's complement
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- -A -> numerical negation of the A-register using 2's complement
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- -M -> numerical negation of the M-register using 2's complement
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- D+1 -> 1 + value of the D-register
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- A+1 -> 1 + value of the A-register
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- M+1 -> 1 + value of the M-register
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- D-1 -> -1 + value of the D-register
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- A-1 -> -1 + value of the A-register
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- M-1 -> -1 + value of the M-register
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- D+A -> value of the D-register + value of the A-register
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- D+M -> value of the D-register + value of the M-register
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- D-A -> value of the D-register - value of the A-register
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- D-M -> value of the D-register - value of the M-register
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- A-D -> value of the A-register - value of the D-register
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- M-D -> value of the M-register - value of the D-register
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- D&A -> bit-wise AND of the values of the D and A registers
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- D&M -> bit-wise AND of the values of the D and M registers
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- D|A -> bit-wise OR of the values of the D and A registers
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- D|M -> bit-wise OR of the values of the D and M registers
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- dest-code:
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If specified, should be followed with a "=" character. Available codes are:
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- D -> write the ALU instruction's output to the D-register
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- A -> write the ALU instruction's output to the A-register
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- M -> write the ALU instruction's output to the M-register
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- AD -> write the ALU instruction's output to the A- and D-registers
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- AM -> write the ALU instruction's output to the A- and M-registers
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- MD -> write the DLU instruction's output to the D- and M-registers
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- ADM -> write the DLU instruction's output to the A-, D- and M-registers
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- jump-code:
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If specified, should be preceded by a ";" character. The computer is fed
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with a programm containing one binary instruction per line. Each of those
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instructions should be seen as having a number, starting at 0 and increasing
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by one. The jump-code lets the computer jump to the instruction of which the
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address is contained in the A-register if the result of the current
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operation satisfies a certain condition. Available codes and corresponding
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conditions are:
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- JEQ -> jump if the output is equal to 0
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- JLT -> jump if the output is lower than 0
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- JLE -> jump if the output is lower than 0 or equal to 0
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- JGT -> jump if the output is greater than 0
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- JGE -> jump if the output is greater than 0 or equal to 0
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- JNE -> jump if the output is not 0
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- JMP -> just jump wathever the output
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- Examples:
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@3 // Set A to 3
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0;JMP // unconditional jump to code line 3.
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@42 // Set A to 42
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D=D-A;JEQ: // Set D to D-A. if D-A == 0, jump to code line nb 42.
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@i // Point onto var i, the real RAM address is handled by the assembler
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M=A // Set corresponding value to it's own address
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A=A+1 // Point to the RAM address just after i
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## Labels
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`"(" LABEL_NAME ")"`
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When performing a jump, the appropriate line of code should be put in the
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A-register. Setting directly the line number with a `@integer` instruction
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is delicate since one has to figure out the line number ignoring comments,
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blank lines, etc... And all the addresses have to be updated if the beginning of
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the assembly code is edited afterward.
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So the assembly language proposes to mark lines with a label using the `(LABEL)`
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syntax. The assembler will then automatically adjust any `@LABEL` instruction
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to match the desired code line at assembly time.
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Example:
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// This code runs a loop 42 times and then stops in an infinite empty loop
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00 @MAIN // @2
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01 0;JMP
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(MAIN)
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02 @42 // Set D to 42
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03 D=A
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04 @DECREMENT // @6
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05 0;JMP
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(DECREMENT)
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06 D=D-1 // Decrement D
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07 @END // @11
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08 D;JEQ // Go there if D==0
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09 @DECREMENT // Or continue the loop
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10 0;JMP
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(END)
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11 @END // Infinity loop to end the programm
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12 0;JMP
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"""
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import sys
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import re
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def create_symbol_table():
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# Erzeugen eines dict
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return {
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key: (value)
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for key, value in {
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**{'@SP': 0,
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'@LCL': 1,
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'@ARG': 2,
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'@THIS': 3,
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'@THAT': 4,
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'@SCREEN': 0x4000,
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'@KBD': 0x6000,},
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**{f'@R{i}': i
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for i in range(16)}
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}.items()}
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def asm(file):
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symbol_table = create_symbol_table()
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print(symbol_table)
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regex = r"^\n"
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asmfile = open(file, 'r')
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asmlines = asmfile.readlines()
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asm =[]
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#print(asmlines)
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for l in asmlines:
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if l.startswith('//'):
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pass
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elif re.match(regex, l):
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pass
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else:
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asm.append(l.replace('\n', ''))
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print(l)
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print(asm)
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print (sys.argv)
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asm_file = asm(sys.argv[1])
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