Decoding MIPS Assembly

1. Decoding MIPS Assembly

2. MIPS Memory • MIPS • 32 and 64 bit versions • 32 bits for • Data width • Instruction size • Address space • 232 ~ 4 billion addresses

3. MIPS Memory • 232 ~ 4 billion addresses • Assigned to bytes • 32 bits : 4 GB addressable memory

4. OS & Memory • OS generallyreserves memory fordevices andcritical OS code

5. MIPS Memory • MIPS takes top half of space • Program space • 0x00000000-0x7FFFFFFF • ~2GB

6. MIPS Memory • Text : code • Data : • Static : allocated by assembler • Dynamic : allocated by OSat run time (heap) • Stack : local variable storage • Managed by compiler

7. Memory Units byte — eight bits. word — four bytes, 32 bits double word — eight bytes, 64 bits • Addresses in bytes, instructions/data often words

8. Dissection • A simple program: • #XXX Comment • .XXX Assembler directive • XXX: Label

9. Directives • Common directives: • .text # the succeeding lines contain instructions • .data # the succeeding lines contain data • .globl name # name is global symbol (visible to code in other files) • .asciiz# store a null terminated string

10. Labels • Label : human readable alias for location in code • Can be on same line or line before named code • Assembler replaces label with named thing/address:

11. Main • Global main tells OS whereto start • MARS doesn't need • Well behaved program should also tell OS when it is done… later

12. An Instruction • Instructions combine registers or literal valuesput results in registers

13. Instruction • Registers • Can use register #or memnonic • Don't use 0 or 1!!!

14. Instruction • An instruction:

15. Standardized Format • Op Operation code • RsFirst source register operand • RtSecond source register operand • Rd Destination register operand • ShamtShift amount - used in shift instructions • FunctSelect the variant of the operation in the op code field

16. Instruction • An instruction: