Computer Architecture

1
Computer Architecture

• MIPS Simulator and Assembly language.

2
MIPS AND SPIM

• SPIM IS A SIMULATOR THAT RUNS PROGRAMS FOR THE
  MIPS R2000/R3000 RISC (REDUCED INSTRUCTIONS SET
  COMPUTER).
• SPIM IS BASED ON A VIRTUAL MACHINE ( A SIMULATION
  OF THE ACTUAL MICROPROCESSOR).
• SINCE SPIM IS A SIMULATOR CERTAIN THINGS ARE NOT
  IDENTICAL TO THE ACTUAL COMPUTER
• TIMING.
• MEMORY CACHES OR MEMORY LATENCY.
• DELAYS FOR FLOATING POINT OPERATIONS OR
  MULTIPLICATIONS OR DIVISIONS.

3
MIPS AND SPIM

• INFORMATION ON THE ASSEMBLY LANGUAGE CAN BE FOUND
  IN
• APPENDIX A OF THE TEXT FOR COMPUTER ARCHITECTURE
• BY GOING TO THE WEB SITE www.cs.wisc.edu/larus/s
  pim.html AND DOWNLOADING THE PDF FILE OF APPENDIX
  A OF THE TEXT
• THE BACK COVER OF THE TEXT HAS A SYNOPSIS OF THE
  ASSEMBLY LANGUAGE INSTRUCTIONS.

4
MIPS AND SPIM

• Assembler syntax
• Comments start with a . Everything from the the
  sharp sign to the end of the line is ignored.
• Identifiers are a sequence of alphanumeric
  characters, underbars ( _ ) and ( . ) that do
  not begin with a number.
• Opcodes for instructions are reserved words that
  are not valid identifiers.
• Labels are declared at the beginning of a line
  followed by a colon
• Item .word 1
• Strings are enclosed in double quotes.
• Special characters follow C , newline \n, tab
  \t, quote \ .
• .align n --- Align the next data on a 2
  raised to the n power bytes boundary.
• .align 2 means aligns the next value on a
  word boundary (4 bytes)

5
MIPS AND SPIM

• .ascii str ---- Store the string in memory, but
  do not null-terminate it.
• .asciiz str ---- Store the string in memory and
  null terminate it.
• .byte b1, ., bn ---- Store the n values in
  successive bytes in memory.
• .data ltaddrgt --- The following data items
  should be stored in the data segment. If the
  argument addr is present the arguments are stored
  beginning with address ltaddrgt.
• .double d1, .., dn ---- Store the n floating
  point double precision numbers in successive
  memory locations.
• .extern sym size ----- Declare that the data
  stored in sym is size bytes large and it is a
  global symbol. This directive allows the
  assembler to store the datum in a portion of the
  data segment that is efficiently accessed via
  register gp .
• .float f1, ,fn ---- Store the n floating
  point single precision numbers in successive
  memory locatoions.

6
MIPS AND SPIM

• .globl sym Declare that symbol sym is global
  and can be refernced from other files.
• .half h1, , hn ----Store the n 16-bit
  quantities in successive memory halfwords.
• .kdata ltaddrgt ---- The following data items
  should be stored in the kernel data segment. If
  argument addr is present, the items are stored
  beginning with address ltaddrgt.
• .ktext ltaddrgt ----- The next items are put in
  the kernel text segment. In SPIM these items may
  only be instructions or words. If the argument
  addr is there, the items are stored beginning
  with address ltaddrgt.
• .space n ---- Allocate n bytes of space in the
  current segment (which must be the data segment
  in SPIM).
• .text ltaddrgt ----- The next items are put in the
  user text segment. In SPIM these items may only
  be instructions or words. If the argument addr
  is there, the items are stored beginning with
  address ltaddrgt.

7
MIPS AND SPIM

• .word w1, , wn ----- Store the n-32 bit
  quantities in successive memory words.
• SYSTEM CALLS
• SPIM provides a small set of operating-system
  like services through the system call
  instruction. To request a service a program loads
  the system call code into register v0 and the
  arguments into registers a0 a3 (or f12 for
  floating point values)
• print_int , the code is 1 , the argument
  goes in a0 integer
• print_float, the code is 2 , the argument goes
  to f12 float
• print_double, the code is 3, the argument goes
  into f12double
• print_string, the code is 4, the argument goes
  into a0string
• read_int, the code is 5, the result goes in v0

8
MIPS AND SPIM

• read_float, the code is 6, the result goes in
  f0
• read_double, the code is 7, the result goes in
  f0
• read_string, the code is 8, the argument is
  a0buffer, a1length
• sbrk , the code is 9, the argument is
  a0amount, the result is address in v0
• exit, the code is 10
• For example to print the answer 5, use
• .data
• str .asciiz the answer .text li
  v0, 4 la a0, str
• syscall li v0, 1 li a0,
  5 syscall

9
MIPS REGISTERS

• NAME NUMBER USAGE
• zero 0 Constant 0
• at 1 Reserved for assembler
• v0 2 Expression evaluation and result of
  a function
• a0 4 Argument 1
• a1 5 Argument 2
• a2 6 Argument 3
• a3 7 Argument 4
• to-t7 8-15 Temporary (not preserved
  across call).

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MIPS REGISTERS

• s0- s7 16-23 Saved Temporary (preserved
  across call)
• t8 and t9 24, 25 Temporary (not preserved
  across call)
• k0, k1 26, 27 Reserved for OS kernel
• gp 28 Pointer to global area
• sp 29 Stack Pointer
• fp 30 Frame pointer
• ra 31 Return address (used by function
  call)

11
MIPS REGISTERS

• MIPS CONTAINS 32 GENERAL PURPOSE REGISTERS.
• REGISTER 0 ALWAYS CONATINS THE HARDWIRED 0
  VALUE.
• REGISTERS at, k0, k1 ARE RESERVED FOR USE BY
  THE ASSEMBLER AND THE OS.
• REGISTERS a0-a3 ARE USED TO PASS THE FIRST 4
  ARGUMENTS TO ROUTINES (REMAINING ARGUMENTS ARE
  PASSED ON THE STACK).
• REGISTERS v0 - v1 ARE USED TO RETURN VALUES
  FROM FUNCTIONS.
• REGISTERS to - t9 ARE CALLER SAVED REGISTERS
  FOR TEMPORARY QUANTITIES 9NOT PRESERVED ACROSS
  CALLS)

12
MIPS REGISTERS

• REGISTERS s0 - s7 ARE CALLEE SAVED REGISTERS
  THAT HOLD LONG LIVED VALUES THAT SHOULD BE
  PRESERVED ACROSS CALLS.
• REGISTER sp POINTS TO THE FIRST FREE LOCATION ON
  THE STACK.
• REGISTER fp IS THE FRAME POINTER.
• REGISTER ra HAS THE RETURN ADDRESS FOR A CALL
• REGISTER gp POINTS TO THE MIDDLE OF TH E64 K
  BLOCK MEMORY OF THE HEAP THAT HOLDS GLOBAL
  VARIABLES AND CONSTANTS.