Memory Mapped I/O

Question 1

What are the control registers

Answer 1

Control registers are flip flops which can be used for reading/ writing AND connected to other circuits

Question 2

What are the two methods for a CPU to interact with the control registers

Answer 2

I/O instructions included in the processors instruction set
Memory Mapped I/O, registers with addresses reserved in memory space

Question 3

What are some factors which affect the choice between using memory mapped I/O and using I/O instructions

Answer 3

The size of the address space
The addressing mode
The size of the instruction set
Any caching complications

Question 4

C assumes Von-Neumann Architecture (single address space), but Memory mapped IO contradicts this by having registers separate to RAM, how can we get around this

Answer 4

We can use a offset for the start of the address space such that C views it as one big address space

Question 5

What type should unsigned, 8 bit registers be represented with in c

Answer 5

uint8_t

Question 6

What does the _BV(bit) macro do

Answer 6

The _BV(bit) macro allows for a byte value with a singular bit in the set position set

#define _BV( bit ) ( 1<<(bit))

Question 7

What does register |= _BV(2); do

Answer 7

Sets bit 2 in register to true

Question 8

What does register &= ~(_BV(2)); do

Answer 8

Sets bit 2 in the register to false

Question 9

What does register ^= _BV(2); do

Answer 9

Toggles bit 2 in the register