Machine & Assembly Language

Machine Language  Computer languages cannot be read directly by the computer – they are not in binary.  All commands need to be translated into binary instructions called machine language.  Each type of CPU has its own machine language.

Von Neumann Architecture CPU Control Unit ALU Registers Memory

Slightly More Complete Picture CPU Control Unit ALU Registers Memory Secondary Storage

Von Neumann Architecture  Program and Data are both stored in memory.  Fetch, Decode, Execute cycle…

Machine Language  We will look at a simulated CPU provided by the author of our book…  This machine language has only 12 different instructions  Each instruction is 16 bits long.  Data values are also limited to 16 bits.

Sample Instruction LOAD contents of memory location into register RR MMMMM example: R0 = Mem[3] Instruction IDRegister #Memory Location

Machine Language LOAD contents of memory location into register RR MMMMM ex: R0 = Mem[3] STORE contents of register into memory location RR MMMMM ex: Mem[4] = R MOVE contents of one register into another register RR RR ex: R0 = R

Machine Language ADD contents of 2 registers, store result in third RR RR RR ex: R0 = R1 + R SUBTRACT contents of 2 registers, store result into third RR RR RR ex: R0 = R1 – R Halt the program

Sample Machine Language Program Add the contents of register 1 to the contents of register 2 and store it in register 0:

Sample Machine Language Program Add the contents of memory location 1 to the contents of register 2 and store it in register 0:

Assembly Language  Set of mnemonic names for the instructions in a particular computer's machine language.  Works on registers and memory locations in the computer.  Translated into binary instructions.

Assembly Language Load contents of memory location into register LOAD [REG] [MEM] ex: R0 = Mem[3] LOAD R0 3 Store contents of register into memory location STORE [REG] [MEM] ex: Mem[4] = R0 STORE 4 R0 Move contents of second register into first register MOVE [REG1] [REG2] ie: R1 = R2 MOVE R1 R2

Assembly Language Add contents of 2 registers, store result in third. ADD [REG] [REG] [REG] ex: R0 = R1 + R2 ADD R0 R1 R2 Subtract contents of 2 registers, store result into third SUB [REG] [REG] [REG] ex: R0 = R1 – R2 SUB R0 R1 R2 Halt the programHALT

Sample Assembly Language Add the contents of register 1 to the contents of register 2 and store it in register 0: ADD R0 R1 R2 HALT

Sample Machine Language Add the contents of memory location 1 to the contents of register 2 and store it in register 0: LOAD R1 1 ADD R0 R1 R2 HALT

Sample Program LOAD R2 5 ADD R2 R2 R2 LOAD R1 3 ADD R3 R1 R2 HALT What does this program do?

Exercise  What would be the assembly instructions to swap the contents of registers 1 & 2?  STORE [MEM] [REG]  LOAD [REG] [MEM]  MOVE [REG] [REG]  ADD [REG] [REG] [REG]  SUB [REG] [REG] [REG]  HALT

Exercise Solution STORE 1 R1 MOVE R1 R2 LOAD R2 1 HALT

Exercise  What would be the assembly instructions to do the following computation: R0 = Mem[7] + R2 - R3  STORE [MEM] [REG]  LOAD [REG] [MEM]  MOVE [REG] [REG]  ADD [REG] [REG] [REG]  SUB [REG] [REG] [REG]  HALT

Exercise Solution SUB R2 R2 R3 LOAD R1 7 ADD R0 R1 R2 HALT (we want R0 = Mem[7] + R2 - R3)

Some More Instructions…  We are missing some crucial functionality…  ??

Some More Instructions…  We are missing some crucial functionality…  Loops! Branch to a location in memory BRANCH [MEM] Branch if the ALU result is zero. BZERO [MEM] Branch if the ALU result is negative. BNEG [MEM]

A More Complex Example 0ADD R3 R2 R3 1SUB R0 R0 R1 2BZERO 4 3BRANCH 0 4MOVE R2 R3 5HALT R03 R11 R2Number R30

In Python  The same program in Python would be the following: z = 0 x = 3 while x != 0: z += y x = x -1 y = z  Or the following: y = y*3

Compilers, Interpreters, Assemblers  Because it is not fun to program in Assembly, we have “high level” programming languages. Python Alice C, C++, Java, Fortran, Cobol, Pascal, C++, M, Ada, lisp, Ruby, Smalltalk, C#, … Compiler/Interpreter translates from the high- level language to machine language.

Program Translation z = 0 x = 3 while x != 0: z += y x = x -1 y = z ADD R3 R2 R3 SUB R0 R0 R1 BZERO 4 BRANCH 0 MOVE R2 R3 HALT CompilerAssembler