registers-memory
See also: Local vs non-local variables
| Register | Memory |
|---|---|
| Contains [local] data currently being processed | Contains program instructions and data that the whole program requires for execution (data that must survive function calls) |
| Small amount of data | Larger amount of data |
| Memory locations that are directly accessible by CPU | RAM (primary memory, internal to CPU) and hard drive (secondary memory, external to CPU) |
| Faster access by CPU (one CPU clock cycle) | Slower access by CPU |
Source: samek-embedded
Registers
Some special registers are described in the following.
Program counter (PC)
- The
PC(Program Counter) register holds the memory address of the current instruction to be executed. - Every instruction increments
PCas a side effect.
Link register (LR)
- The
LRlink register remembers the place in the code to return to after a branch function completes - Modified as a result of the
BLinstruction
Stack pointer (SP)
- Points to the top of the stack .
Memory
Visualisation of memory
Each address holds one unit of memory (a byte)
Example: the RAM on TM4C123G
- RAM is located from the address 0x2000'0000 up to 0x2000'7FFFF
- The RAM contains $8000_{16} = 32768_{10}$ units of memory (bytes)
$$ \begin{aligned} 32 768 \text{~B} &= \frac{32 768}{2^{10}} \text{~KB} = \frac{32 768}{1024} \text{~KB}\
&= 32 \text{~KB or } 32 \text{~KiB} \end{aligned} $$