Build A RISC-V Chip From Scratch
  • Tutorial
    • Overview
    • RISC-V Basics
    • Datapath
      • R-type
      • I-type
      • S-type
      • B-type
      • U-type
      • J-type
    • Single Cycle
      • Implementation
      • More Fun
    • Pipelined
  • Interfaces
    • Graphics
      • VGA
      • HDMI
      • Draw an image using FPGA
    • Serial Interface
      • UART and FIFO
      • Echo
      • Memory Controller
  • Tools
    • Install vivado 24.1
    • Get started with vivado 24.1
    • Get started with quartus
    • FPGA build flow
    • Tcl
    • Verilog testbench
    • Open-source tools for FPGA development
      • iverilog
      • nextpnr
    • RISC-V Toolchain
      • RISC-V Toolchain Installation
      • RISC-V Toolchain Usage
  • Devices
    • Alinx AX7020
    • DE10-Stanard
  • Misc
    • Input Conditioning Circuits
    • Build A RISC-V Soft Core CPU
    • Introduction to FPGA
    • Clock Wizard
    • What is an IP core?
    • Test and Debug Soft Cores
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On this page
  • I-Format Instruction Layout
  • I-immediate
  • I-Format Arithmetic Instructions
  • Adding I-Format arithmetic instructions to datapath
  • I-Format Load Instructions
  • Adding load instructions to datapath
  1. Tutorial
  2. Datapath

I-type

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Last updated 8 months ago

I-Format Instruction Layout

  • The funct7 and rs2 fields from R-format are replaced by 12-bit signed immediate, imm[11:0] (in range [-2048, 2047]).

  • Remaining fields (rs1, funct3, rd, opcode) same as R-format.

  • Immediate is always sign-extended to 32-bits before use in an arithmetic operation.

I-immediate

I-Format Arithmetic Instructions

Adding I-Format arithmetic instructions to datapath

I-Format Load Instructions

Load instructions are also I-type.

  • Reg[rd] <- Mem[Reg[rs1] + offset]

    • The 12-bit immediate is added to the base address in rs1 to form the memory address

    • The value loaded from memory is stored in register rd

Note that the funct3 field is to specify the width (i.e., the amount of bytes) and signedness of load data.

Adding load instructions to datapath

Immediate generator generates I-type immediate
I-Format Arithmetic Instructions
Load Instruction Layout
I-Format Load Instructions