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// embedded systems project

FreeRTOS on RISC-V

FreeRTOS ported to 64-bit RISC-V and booted on QEMU, from the startup code and linker script up.

A port of the FreeRTOS kernel to RV64 on QEMU's virt machine: bare-metal startup in assembly, a linker script that lays out RAM from 0x80000000, machine-mode timer interrupts driving a 1 kHz tick, and two preemptive tasks that prove the scheduler. Built for the CENG507 embedded systems course.

source
// chip18/21
year
2026
type
embedded systems project
group
systems

the problem

//01the problem

A real-time OS hides the hardware from applications, but first someone has to tame the hardware: start the core with no firmware, lay out memory, take the timer interrupt and save every register on a context switch. The goal was to do that by hand on an open instruction set.

how it works

//02how it works

  1. 01

    Bare metal, from the reset vector

    An assembly startup file sets up the stack and jumps to C with no BIOS at all. A linker script places code, data and a 64 KB stack in RAM from 0x80000000 on QEMU's virt machine.

  2. 02

    The timer drives the scheduler

    The machine-mode timer, through MTIME and MTIMECMP, raises a 1 kHz tick. mtvec points at the FreeRTOS trap handler, which saves the context in assembly and lets the kernel preempt.

  3. 03

    Proven by tasks, checked in the disassembly

    Two tasks with different periods interleave under preemption. The build emits an ELF with symbols, a raw binary and a full disassembly listing, targeting rv64imac_zicsr with the lp64 ABI.

measured

//03measured

1 kHz
scheduler tick
machine-mode timer via mtime and mtimecmp
64 KB
stack laid out by the linker script
ram from 0x80000000 on qemu virt
0
lines of bios
assembly startup jumps straight to c

highlights

//04highlights

  • Boots with no firmware on QEMU's virt machine
  • Preemptive scheduling on a 1 kHz tick, stack overflow checks on
  • RV64IMAC with Zicsr, medany code model
  • Course project for CENG507, Embedded Systems

built with

  • C
  • RISC-V assembly
  • FreeRTOS
  • QEMU
  • GNU toolchain
  • Make

//05contact

Say hello. I read everything.

Email is the fastest way to reach me. For anything that needs a conversation, book a call.

book a callsave contact

to

name
Khaled Saeed
email
contact@khaledsaeed.tech
country
Lebanon