Immediate and register instructions

Many instructions in the RISC-V instruction set have multiple variants:

• An immediate variant
• A register variant

What is an immediate value?

Immediate mode is essentially when we are working with constant values.

For example, consider this addi instruction:

addi x0, x1, 5 

Because we are adding a constant value (5) to the value of register x1, this is an example of an immediate instruction.

In contrast, consider this add instruction:

add x0, x1, x2

Here, we’re not using a constant value, but rather the value stored in register x2. That means this is a register instruction.