/RISC-V_code

Primary LanguageMakefile

RISC-V_code

What is RISC-V

  • open standard ISA based on RISC principals
  • open sourced, deployable in any hardware or software.
  • ARM and x86 charge royalaties.

Architecture

  • 32bit, 64bit & 128bit implementations.

  • 33 registers including $PC , 32 general

    • x0-x31+pc

  • Given seperate identifiers based on use in the RISCV calling convention (x0 = zero, x1 = ra)

    • 6 general purpose
    • 7 temperary(t0-t6) - data doesnt persist
    • 12 saved (s0-s11) - non volatile
    • 8 argument(a0-a7) -

Instruction template

Three register

<operation>	<dst>,<src1>,<src2>

  • addi a2,x0,64

    • $a2 = $zero + 64
    • $a2 = 64

  • la a1, helloworld

    • a1 = address of helloworld label

RISC-V syscall table

  • To do anything have to ask kernel for help

  • Linux syscall table defines how to interact with the kernel.

    • Specifies functions, syscall numbers, arguments required , etc.

  • For ex:- exit syscall 93, write syscall 64

Implementing a syscall

- Set a7 to syscall number
- Set a0 .. to arguments
- Invoke the ecall instruction to call the kernel

System sysscall numbers [https://github.com/westerndigitalcorporation/RISC-V-Linux/blob/master/linux/include/uapi/asm-generic/unistd.h]

Setup

sudo apt install gcc-riscv64-linux-gnu