Lecture 2

Question 1

What is the instruction cycle?

Answer 1

The procedure of processing an instruction by the microprocessor

Question 2

What does a programming model define?

Answer 2

1. What instructions are avaılable
2. How instructions access their operands
3. How instructions are described in the processors assembly language

N.B. Processors with different programming models can offer similar sets of operations but may require VERY different approaches to programming

Question 3

What is a data transfer instruction?

Answer 3

Operations that move data from one place to another. They DON’T modify data, just copies it to destination

Question 4

What is a data operation instruction?

Answer 4

Instructions that modify the data values and store the result

Question 5

What is a program control instruction?

Answer 5

Jump or branch instructions used to go into another part of the program. Jumps can be absolute or conditional (If else)

Question 6

What are the different data transfer instructions?

Answer 6

Load data
Store data
Move data
Input data
Output data

Question 7

What does Input data do?

Answer 7

Instructions that input data from the input device into the microprocessor (e.g. what key was pressed)

Question 8

What does output data do?

Answer 8

Microprocessor copies data from one of its internal registers to and output device (e.g. show what key has been pressed)

Question 9

What does load data do?

Answer 9

Copy data from memory intro microprocessors registers

Question 10

What does store data do?

Answer 10

Similar to load data but data is copied in to opposite direction. Data is saved from internal microprocessor registers into the memory

Question 11

What does move data do?

Answer 11

Move data from one microprocessor register to another

Question 12

Explain how instructions use the stack

Answer 12

Instructions get their operands from the stack and write their results back to the stack

Question 13

What are some advantages of stack based architecture?

Answer 13

Program code takes little memory
- No need to specify the address of the operands in memory or registers
- Push is one exception because it needs to specify the operand

Question 14

What are stack based processors better suited for? Postfix or infix?

Answer 14

Postfix, writing programs for stack-based architectures is not easy

Question 15

What is infix notation

Answer 15

a+b

Question 16

What is postfix notation?

Answer 16

ab+

Question 17

What is needed for an expression to be easy to implement in a stack-based architecture?

Answer 17

Convert it into postfix notation

Question 18

What is a specific to a general purpose register architecture?

Answer 18

• The instructions read and writes to random access register file
• the register file allows the access of any register in any order by specifying the register ID

Question 19

What is the main difference between stack based and general purpose register?

Answer 19

• Repeatedly reading a register will produce the same result and will not modify the state of the register file (which it will in stack-based)
• Programs can choose which values should be stored in the register file at any given time, allowing them to cache most accessed data (in stack, once the data has been used, it’s gone)

Question 20

What does a GPR (general purpose register) need to specify?

Answer 20

• The register that hold their input operands
• And the register that will hold the result

ADD r1, r2, r3

Question 21

What performance metric is the difference between GPR and stack-based?

Answer 21

GPR architectures have better performance but at the expense of needing more storage space for the programs

Question 22

What is the difference between programming GPR architecture processor compared to stack-based?

Answer 22

There are fewer restrictions on the order in which the operations can be executed
- On a stack-based, instructions should execute in the order that would leave the operands for the next instructions on the top of the stack
- On GPR, any order that place the operands for the next instruction in the register file BEFORE that instruction executes is valid
- Operations that access different registers can be reordered without making the program invalid.

Question 23

Compare Stack based and GPR architectures

Answer 23

Stack-based:
- Instructions take fewer bits to encode
- Reduced amount of memory taken up by programs
- Manages the use of register automatically
- Instruction set does not change if size of register file has changed
Still good for certain embedded systems
GPR:
With evolution of technology, the amount of space taken up by a program is less important
- Compilers for GPR achieve better performance with a given number of GPRs than those on stack-based architectures with same numbers of register. The compiler can choose which values to keep (Cache) in register file at any time
Used in modern computers