CODEWITHSUNDEEP
assemblyriscvimmediate-operand
Betty
Betty

Reputation: 161

How to load an immediate number to a register in RV32I Base Instruction Set?

Recently, I am working on RV32I base instruction set, and I did not find any instruction looks like LD r1, imm. Thus, I am wondering how assembly programer load an immediate to a register in RV32I system? Thanks.

To do so, programmer could use ADDI r1, r0, imm. Since r0 is a constant 0, so this instruction move imm to register r1.

I have no idea if the designers of RV32I think this way, use ADDI to replace LD r1, imm?

Hope anyone could shed some lights on it. Thanks.

Upvotes: 7

Views: 20115

Answers (1)

FeelTheBurns
FeelTheBurns

Reputation: 1085

There is a li (load immediate) alias or pseudo instruction that provides the functionality you are referring too.

The following example shows the li pseudo instruction which is used to load immediate values:

.equ  CONSTANT, 0xdeadbeef

li    a0, CONSTANT

Which, for RV32I, generates the following assembler output, as seen by objdump:

00000000 <.text>:
   0: deadc537            lui a0,0xdeadc
   4: eef50513            addi    a0,a0,-273 # deadbeef <CONSTANT+0x0>

This snippet is from this github markdown that is a good reference when programming in riscv assembly. https://github.com/riscv/riscv-asm-manual/blob/master/riscv-asm.md#load-immediate

Upvotes: 8

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