Module 5

Question 1

What is RISC and CISC and explain memory differences

Answer 1

Reduced Instruction Set Computer
- Has fewer instructions available than CISC
- Carries out more, simpler instructions - needs more software as a result
- Works only in registers
- More useful in ES setting

Complex Instruction Set Computer
- More instructions that have highly specialised tasks built in
- Can manipulate operands directly in memory and registers

Question 2

Why is RISC preferred to CISC for ES?

Answer 2

RISC is more cost effective and easier to implement because it often requires less storage too. They are also more power efficient and have smaller physical footprints.

Question 3

What is the ARM Cortex 3-Stage pipeline?

Answer 3

That thing you got wrong in the test look at the memo

Question 4

What is Thumb and why use Thumb

Answer 4

Thumb instructions are half the size of ARM. The system can then load two instructions at the same time, however, this often makes design more complex - fewer instructions to choose from.

Question 5

What is AArch32

Answer 5

32-bit architecture that supports operations on bytes (8), half-words (16), and words (32)

Question 6

What are the modes of operation of the ARM processors?

Answer 6

User mode
- Limitations on register access
IRQ mode
- Low priority interrupt is signaled.
Supervisor mode
- IDk

Question 7

What are the ARM registers?

Answer 7

1 Program Counter
1 Current Program Status Register (CPSR)
5 Saved Program Status Register (SPSR)
30 General Purpose Registers r0 to r14

Question 8

What is the ARM exception vector

Answer 8

32 bytes that go from 0x00000000 to 0xFFFF0000 where each entry has some abort or interrupt instruction.

Question 9

What is Port Mapped IO? ADV and DIS

Answer 9

A special IO address space used to get to devices. There are specific CPU instructions used to access this space.

+ Peripherals can have simpler memory address decoding logic

• Special instructions needed

Question 10

Memory Mapped IO? ADV and DIS

Answer 10

+ No special techniques needed
- Some address space then used for peripherals.
- Uses RAM too

Question 11

How is the volatile keyword useful for memory mapped IO

Answer 11

Volatile tells the compiler to explicitly access memory locations for a variable.

Question 12

How are struct functions used and why are they useful?

Answer 12

typedef struct {
uint8_t item1;
uint8_t item2;

} NAME; //NAME is for the overall structure

volatile NAME* varName = (NAME*) ADDRESS; //varName is the name of this specific structure type.

varName -> item1 = 1; //write to a thing

x = varName ->item2; //read from a thing