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PseudoInstructions

PseudoInstructions. 21 - Extended Assembler. Pseudoinstructions Instructions defined at assembly level Assembler translates to machine intsructions. Intent. Intent signaling instructions. Convenience. lw : Load word with label Sets up base address/offset. Convenience.

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PseudoInstructions

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  1. PseudoInstructions

  2. 21 - Extended Assembler • Pseudoinstructions • Instructions defined at assembly level • Assembler translates tomachine intsructions

  3. Intent • Intent signaling instructions

  4. Convenience • lw : Load word with label • Sets up base address/offset

  5. Convenience • sw : Store register to labeled memory

  6. Load Address • la : Load Address • Get memory address of labeled item • Assembly pointer

  7. Other Pseudo Tricks (23) • Immediate value impliesimmediate instruction • Convenience math/logic

  8. Assembler Temporary Register • Instructions requiring multiple steps built using $1

  9. Registers • Registers have meanings defined by convention • Can use memnonic names instead of numbers

  10. Registers • Tips: • Avoid $0, $1and $26-$31 • $8-$25 safe for now :$t0-$t9 and $s0-$s7

  11. 24 – More Pseudo • Whole bunch o' branches and sets:

  12. Indexed Addressing • Arrays last week: • Move baseaddress around

  13. Unnatural • Offset/Base addressing ofteninconvenient • Indexed Addressing • Label(Offset)Array[i]

  14. Arrays Now • Arrays now • Change offset, uselabel as baseaddress

  15. Interrupts • Interrupt: signal to CPU that something needs to happen • Hardware Interrupts • Input/output ready • Ctrl-C • Code needs help • Trap from math overflow • Request for OS

  16. Interrupt Handling • OS take over • Saves stateof running program • Runs interrupt handler • Restores state

  17. 22 - Syscalls • syscall: program generated interruptOperating System please do something • Use registers to send/receive information

  18. Syscalls • Syscall codes:

  19. MIPS cin / cout • Read and print integer:

  20. More Syscalls • Properly end the program:

  21. Print String • Strings usually longer than word • Live in memory, not registers • String syscalls need pointer to string : $a0 • Prints bytes until null char (00)

  22. Read Print Int 3 Print promptand answermessages:

  23. Read String • Read string code needs • Location to write to • Space available

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