The document provides a detailed comparison of three prominent RISC architectures: MIPS, ARM, and SPARC, discussing their histories, applications, architectural differences, operating modes, and more. It highlights the strengths of each architecture in terms of performance, cost, and suitability for various applications. The conclusion emphasizes the importance of analyzing product requirements to select the most appropriate architecture for prototyping and market competitiveness.

1. Insightful comparison between three of the most popular
and widely used RISC processors: MIPS, ARM and SPARC
Apurv Nerlekar
Rishabh Sreedhara
Rishikesh Nagare
Shivakumar Soppannavar

2. Index
1. Introduction
2. History
3. Applications and market
4. Architectural difference
5. Register conventions
6. Operating modes
7. Addressing modes
8. Conditional execution
9. Exception handling
10 Stack implementation
11.Conclusion

3. Introduction
1. Why do we need to study the differences?
● Every application is different, and hence each application requires different crucial
factors that decide the architecture to use.
● Some may be performance dependent, some crucial with respect to reliability, some
might require to reduce the cost.
2. We will discuss about how to select a specific processor for particular
application along with few use cases.
3. The presentation will help you scale your application and adapt an
architecture which is a best fit.

4. History
Reduced instruction set computing ( RISC ).
● MIPS : Microprocessor without Interlocked Pipeline Stages. - Developed since 1980.
MIPS-32 and MIPS-64 with versions MIPS 1 to MIPS 5
Ex: Embedded systems, Connectivity.
● ARM : Advanced RISC Machines. - Developed since 1985.
Developed because of the emerging trend of low cost machines.
Ex: Mobile devices, Automotive.
● SPARC : Scalable Processor Architecture. - Developed since 1987.
Developed because of the concept of making it compatible for various different
languages to code on and deploy softwares which can provide high performance.
Ex: Network Servers, Mobile Devices.

5. Applications and market
1. MIPS
● Unlike other architectures MIPS has many market applications.
● Open source implementations available.
● Simple coding syntax, easier to use.
● Benefits help them to be used for educational purpose.
● The cost for devices using MIPS is less.
● Support for Graphics, and long term support.
Ex: Few Applications
● MM : Memory Management application .
● MMU : Memory Management Unit.
● Mobile Devices, Networking devices, Audio devices.
Overall : Low cost, huge functionality and high performance gives it a bigger market than
the rest.

6. Applications and market (contd..)
2. ARM
● Support for 64 bit architecture. Continuous updation.
● Development over architecture depending upon the market.
Ex. ARM v8-A for high performance market like mobile devices.
ARM v8-R for embedded devices like automotive, industrial control.
● Variety of units as per demand. Some include virtual platforms, code generation tools,
debug solution tools.
● Every device configured with respect to consume low power.
● Extension approach like java acceleration, SIMD, advanced SIMD, security (Trustzone).
● Support for Graphics, long term support.
Overall : Low cost, adaptability, variety of low power-high performance devices gives it a
bigger market than the rest.

7. Applications and market (cont..)
3. SPARC
● Used majorly by programmers and Architects. Low level programing.
● Multi core functionality introduced by this architecture.
● Use cases include softwares and devices where need for performance with respect to
throughput is required.
● A bit higher on cost than others
● Highest support of Integration with other architectures.
● Multiple servers can be written with the help of Solaris OS which is the best fit.
Overall : Adaptability, Extreme high performance architecture makes it ideal for systems
which are highly concerned about throughput and extreme server processing.

8. Architectural difference
1.MIPS
● Low overhead - less time wasted
● Power Efficient- less number of instructions
2.ARM with Thumb
● Reduced total amount of Memory
● Extra Thumb ISA
● Switching between states
3.SPARC
● Register file model unlike others its not flat

9. Register conventions
Registers referred using:
● MIPS
$ ex: $R0
● ARM
ex: R0
● SPARC %
ex: %R0

10. MIPS
32 bit wide 32 registers
Two special registers:
Hi/Lo -> Multiply and Divide
Units
mfhi $r1
mflo $r0

11. ARM
For ARM Cortex- M3
● 32 bit wide 16 registers
● 12 general purpose registers
Status registers:
● CPSR

12. SPARC
● 32 bit wide 32 Registers
● Registers are divided into four groups.
1. global registers
2. output registers
3. local registers
4. input registers
● Register file model not flat.
● Overlapping register windows.
Procedure Calling Mechanism

13. ARM
Operating modes
User Mode Privileged Mode
System Mode Exception Mode
SVC - Supervisor Mode
UND- Undefined Mode
ABT - Abort Mode
IRQ- Interrupt Mode
FIQ- Fast Interrupt Mode
MIPS
Kernel Mode User Mode
SPARC
Supervisor Mode User Mode

14. M
I
P
S
Operating Modes - MIPS and SPARC
kernel mode, (Status Bit - 0)
● Can access and change all registers.
● This mode has the privilege over other modes and gets switched to in case of an
error, interruption, exception or at power up
User mode, (Status Bit - 1)
● Accessed by users and has a lower privilege than that of the kernel mode.
● It also prevents different users from interfering with one another
kernel mode, (Status Bit - 0)
● Used to access the processor state registers, such as the Window Invalid Mask (WIM), and the
input/output devices.
● Full access to the memory and its system tables making it privileged in almost all architectures.
User mode, (Status Bit - 1)
● Used to write to and read from the processor state register and has a limited access to the memory
since a load or a store instruction cannot be executed in it.
● Additionally, to know whether the processor is in the user mode or in the supervisor mode, the
processor status word is used to determine the current state of the processor
S
P
A
R
C

15. Operating Modes - ARM
ARM has seven basic operating modes, starting with the processor mode which has two operating
modes under it, the user mode and the privileged mode.
1. User mode
The user mode is where most applications’ contents or operating systems’ tasks run.
2. Privileged mode
The privileged mode has under it two operating modes, system mode and the exception mode.
❖ System mode is the privileged mode which uses the same registers as used by the user mode
❖ Exception mode has 5 operating modes
1. Supervisor mode (SVC) which is entered under two conditions, when on restore or when Software
Interrupt Instruction (SWI) is executed
2. Abort (ABT) mode which is used to handle memory access violations
3. Undefined (UND) mode which is used to handle undefined instructions
4. Interrupt (IRQ) mode which is entered when a high priority interrupt is raised.
5. Fast Interrupt (FIQ) mode which is entered when a high priority interrupt is raised

16. Operating Modes - ARM - Register Organization

17. Addressing modes
Addressing modes are the ways how architectures specify the address of an object they want to
access.
MIPS
SPARC
ARM
1. Register Addressing
2. Immediate
3. PC-Relative
4. Pseudo-direct
5. Base
1. Pre indexed Addressing
2. Pre indexed Addressing with write back
3. Post indexed Addressing
4. Program counter Relative Addressing
1. Register indirect with index
2. Register indirect with immediate

18. Addressing modes - MIPS
MIPS support five addressing modes:
1. Register Addressing: This mode is mainly used in calculating the effective address of the jump register (jr)
instruction. Ex: Jump $R3; ADD $R5, $R6, $R7
2. Immediate Addressing: This mode does not access memory and thus is relatively faster than other modes.
The immediate is of size equal to 16-bits. Ex: ADD $R1, $R1, 10; i.e R1= R1+100
3. PC-Relative Addressing: This mode is used to determine when the branch instruction occurs by summing the
offset value with the PC. EX: BEQZ $R5, Loop;
4. Pseudo-direct Addressing: This mode is used in the jump instruction where the value of the offset is 6-bits
and the target of the instruction jumped to is 26-bits. The upper four bits of the PC and the least two
significant bits, which are 00, are all concatenated with the 26-bit immediate resulting in a 32-bit
instruction. EX: MOVE $R1, $R2 means move value of $R2 into $R1, this is translated into actual code like Add
$R1, $R1, $ZERO
5. Base Addressing: This mode is used in store word and load word instructions. It is known as the indirect
addressing since the register acts as a pointer to some memory location whose address could be found in the
register. EX: LW $R1, 24($R1); Address is the sum of the register and constant 24

19. Addressing Mode - ARM
ARM supports multiple addressing modes, including modes that allow direct bit shifting. There are four main
addressing modes to calculate the effective address:
1. Pre-indexed Addressing: In this mode, the source/destination address is stored in a register offset by
another value. Figure 1 (a), shows how the load operation is used to calculate the pre-indexed
effective address. EX: LDR R3, [R5, R6]
2. Pre-indexed Addressing with Write Back: In this mode, it is sometimes useful to save the new address
in a register. To indicate that this effective address is being written back, add an exclamation mark (!)
at the end of the load instruction. Figure 1 (b) describes the operation of the write back. EX: LDR R3,
[R5, R6]!
3. Post-Indexed Addressing: This mode is similar to Pre-Indexed Addressing with Write back. However,
the address is modified and saved only after the load/store operation. Figure 1 (c) illustrates the
effective address calculation in the post-indexed addressing mode. EX: LDR R3, [R5], R6
4. Program Counter Relative Addressing: This mode allows the ARM architecture developers to address
memory relative to the Program Counter (R15). LDR R0, [R15, #24]

20. Addressing Mode - ARM (cont..)
Pre-indexed addressing
mode
Pre-indexed addressing
mode with write back
Post-indexed addressing
mode

21. Addressing mode -SPARC
SPARC supports two addressing modes to compute the effective address:
1. The Register indirect with index: This mode computes the effective address by adding the contents of the
base register to those of the index register. The effective address cannot be equal to only the base register but
the index register could be made equal to zero and by that the effective address will be equal to the base register.
E.g: Add %i3, %i1, %i2
Typically used to access array where one register holds the base value and other holds the (scaled) index of the
element
2. The Register indirect with immediate: This mode computes the effective address by sign extending the
13-bit immediate to 64 bits and then adds the contents of the base register to it. The effective address could be
made equal to the base register by making the constant equal to zero.
E.g: Add %o1, 4, %o2

22. Stack implementation
A stack is a data structure that is used for the storage of data.
MIPS ARM SPARC
Direction of
Stack growth
Stack grow
downwards
Stack grow
downwards and
upwards
Stack grow
downwards
Push and Pop
instruction
Does not support
push/pop
instructions.
Instead, it
manipulates the
stack pointer
(register 29)
No explicit
push/pop
instructions but it
can manipulate the
stack pointer to do
so
No explicit push/
pop instructions
but can be
implemented using
the stack pointer
(sp)

23. Stack implementation - Stack Popping
Stack popping. The stack pointer (SP) copies the data, in the address given, in a register first,
and then moves the stack pointer.
Initial Stack
After
adjusting
SP
Empty
Data
Stack
SP SP
SP
Empty
Data
Stack
Empty
Data
Stack
000FFFFC
00100000
000FFFFC
00100000
000FFFFC
00100000
After
Copying

24. Stack implementation - Stack Pushing
Stack pushing. The stack pointer (SP) is moved in order to place the contents of register 3 (R
[3]) into the address that the stack pointer is pointing to.
Initial Stack
After
Copying
Empty
Stack
SP
SP SPEmpty
Stack
Empty
R[3]
Stack
000FFFFC
00100000
00100000
000FFFFC
00100000
After
Adjusting
SP

25. Conditional Execution
Advantage of conditional statements is that, we can make certain statements to execute
conditionally.
MIPS
No Conditional bits
depends on branch instructions
Example:
beq $5, $13, label1

26. ARM
Four Conditional Flags:
● Zero (Z), Overflow(V), Carry (C), Negative (N)
Data processing instructions do not affect the conditional flags
postfix the instruction with letter “s”
Example:
ADDS r0, r1, r2
Data processing Instructions:
Arithmetic operations, comparisons, logical operations, data movement between registers.
SPARC
Four Conditional flags:
● Zero (Z), Overflow(V), Carry (C), Negative (N)
Suffix “cc” to operations
Example:
ADDc Rs1, Rs2, Rd
ADDccc Rs1, Rs2, Rd

27. Exception handling
Normal execution of instructions may be interrupted when an exception occurs.
Are 2 types:
● Synchronous exceptions: occurs at the same place every time a program is executed
● Asynchronous exceptions: happen with no temporal relation to the program being executed
Register Number Register Name Usage
8 BadVAddr This holds Memory address where exception occurred
12 Status Masks the Interrupts, enable bits, and changes status when
exception occurred
13 Cause Type of exception occurred and pending interrupt bits
14 EPC Holds Address of instruction that caused exception
MIPS
Cause Register Pending Interrupt Exception Code
Bits 15-10 Bits 5-2

28. Exception handling
ARM
● Exception happens only in ARM mode.
● Core copies CPSR and is saved in SPSR.
● CPSR is updated with ARM state, CPU to exception mode, interrupts are disabled.
● PC is set to interrupt vector address.
SPARC
● When Exception occurs Trap Enable gets cleared
● Execution state changes to supervisor mode
● Current window pointer is decremented
● Program counter, processor state register, NPC are saved to local registers %l0 to %l2
● trap handling code is saved to %l3 to %l7

29. Conclusion
We conclude that once the detail analysis of your product is done and If
the tables and flowcharts from this presentation is followed, it can help
us decide which architecture to choose before even starting the
prototyping of product.
This will help making the product competitive and help them keep
updated in the market with high assured performance.

30. References
[1] A. I. Center., ARM Information Center. N.p., n.d.
[2] B. J. Catanzaro, Ed., The SPARC Technical Papers. New York, NY, USA: Springer-Verlag
New York, Inc., 1991.
[3] C. Corporation, Best Practices For Improving Application Performance and Lowering Cost
by Managing MIPS., 2012.
[4] R. Teodorescu, Instruction Set Architecture of MIPS Processor Presentation B. The Ohio
State University, 2008.
[5] C. Lin, Understanding the Stack. Department of Computer Science, University of Maryland,
2003.

31. Thank you