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SPIM and MIPS programming

SPIM and MIPS programming. 6. 8 bits of data. 5. 8 bits of data. 4. 8 bits of data. 3. 8 bits of data. 2. 8 bits of data. 1 . 8 bits of data. 0. 8 bits of data. Review: Memory Organization. Large single-dimension array A memory address is an index into the array

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SPIM and MIPS programming

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  1. SPIM and MIPS programming

  2. 6 8 bits of data 5 8 bits of data 4 8 bits of data 3 8 bits of data 2 8 bits of data 1 8 bits of data 0 8 bits of data Review: Memory Organization • Large single-dimension array • A memory address is an index into the array • Memory stores 8 bits in each address • Registers store 32 bits of information • For example: • Li $t0, 0 • lw $t0, 0($t1) • Then $t0 will contain the data of the first four memory locations

  3. Review: Registers • MIPS has 32 registers, each containing 32 bits • Some registers are listed below • $zero: constant 0 • $at: reserved for the assembler • $v0 - $v1: function results • $a0 - $a3: function arguments • $t0 - $t9: temporary • $s0 - $s7: temporary

  4. Arithmetic Instructions (1/2) • Some instructions include: • Add • Subtract • Multiply • Divide • Must break expression into simple operations • use temporary registers ($t0 to $t9) to store intermediate results • use load to insert a value into a variable • use store to assign a value to a variable

  5. Instructions InstructionMeaning • add $s1, $s2, $s3 $s1 = $s2 + $s3 • sub $s1, $s2, $s3 $s1 = $s2 – $s3 • lw $s1, 100($s2) $s1 = Memory[$s2+100] • sw $s1, 100($s2) Memory[$s2+100] = $s1

  6. Global variables C programAssembly Program int variable = -42; .data variable: .word -42 int r1; r1: .space 4 .space allocates empty space in bytes .word allocates 4-byte value followed by the value to store

  7. Assember Directives • All assembler directives have names that begin with a period (`.'). • Examples: • .word w1 • allocate a 4-byte word • .half h1 • allocate 2-bytes • .byte b1 • allocate a single byte • .ascii “hello" • allocate a sequence of bytes and store ASCII values • .asciiz “hello" • allocate a sequence of bytes and store ASCII values. terminate string with 0 byte (end of string) • .float • .double

  8. Input/Output • On real machines (including real MIPS computers), I/O is very complicated • usually handled by operating system • In SPIM, I/O is managed by system calls • syscall instruction • SPIM suspends simulation to perform I/O, then resumes simulation

  9. System calls • Systems calls are used to interact with the user • To make a system call • determine which service you want • put service’s call code in register $v0 • put arguments in registers $a0, $a1, etc. • execute the syscall instruction • results are in registers $v0, $v1

  10. System calls

  11. .data value: .space 4 .text main: li $v0, 5 #Syscall 5: read int syscall sw $v0, value #Number is in $v0 li $v0, 1 #Syscall 1: print int lw $t0, value mul $a0, $t0, $t0 #$a0 is what to print syscall li $v0, 10 #Exit syscall Input/Output: Numbers

  12. .data msg: .asciiz "Type a string: " buff: .space 20 .text main: li $v0, 4 # print string la $a0, msg # $a0: address of string syscall li $v0, 8 # read string la $a0, buff # $a0: max length of buffer li $a1, 20 # $a1: max length of string syscall li $v0, 4 la $a0, buff syscall li $v0, 10 # exit syscall Input/Output: strings

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