Question

What list the three branching operands in MIPS. Explain each.

Answer 1

When MIPS instructions are classified according to coding format, they fall into three categories: R-type, I-type, J-type.

Machine Language: R Format
------------------------------------

• Instructions, like registers and words of data, are also 32 bits long
– Example: add $t0, $s1, $s2
– registers have numbers, $t0=9, $s1=17, $s2=18

000000

10001

10010

01000

00000

100000

op

rs

rt

rd

shamt

funct

R-Format Example:

• add $8,$9,$10

Translate the above instruction.Specifically: Look up “add” on green card. As you can see, “add” is R format.

Look up the R format and the opcode/funct values for add. Then, fill in the tables and the underline below.

0

9

10

8

0

32

Binary number per field representation (use the right # of bits!):

000000

01001

01010

01000

00000

100000

hex representation: __0x012A4020

Machine Language: I format

---> Consider the load-word and store-word instructions,

– What would the regularity principle have us do?

– New principle: Good design demands a compromise

---> Introduce a new type of instruction format

– I-type for data transfer instructions

– other format was R-type for register

Example: lw $t0, 32($s2)

35

18

9

32

op

rs

rt

16 bit number

I-Format Example:

MIPS Instruction: addi $8,$9,7 $8 is rt; $9 is rs.

This instruction adds 7 to the contents of $9 and stores it in $8.

Translate the instruction above to fill in the following tables:

Decimal number per field representation:

8

9

8

7

Binary number per field representation:

001000

01001

01000

0000000000000111

Hex representation:__0x21280007

Machine Language: J Format

---> Jump (j) , Jump and link (jal) instructions have two fields

– Opcode

– Address

---> Instruction should be 32 bits (Regularity principle)

– 6 bits for opcode

– 26 bits for address

op	26 bit address

MIPS Instruction Formats:

---> simple instructions all 32 bits wide

---> very structured, no unnecessary baggage

---> only three instruction formats

R

op

rs

rt

rd

shamt

funct

I

op

rs

rt

16 bit number

J

op	26 bit address