A minimalist RISC-V system emulator capable of running Linux the kernel and corresponding userland.
semu
implements the following:
- RISC-V instruction set architecture: RV32IMA
- Privilege levels: S and U modes
- Control and status registers (CSR)
- Virtual memory system: RV32 MMU
- UART: 8250/16550
- PLIC (platform-level interrupt controller): 32 interrupts, no priority
- Standard SBI, with the timer extension
- Three types of I/O support using VirtIO standard:
- virtio-blk acquires disk image from the host.
- virtio-net is mapped as TAP interface.
- virtio-snd uses PortAudio for sound playback on the host with one limitations:
- As some unknown issues in guest Linux OS (confirmed in v6.7 and v6.12), you need
to adjust the buffer size to more than four times of period size, or
the program cannot write the PCM frames into guest OS ALSA stack.
- For instance, the following buffer/period size settings on
aplay
has been tested with broken and stutter effects yet complete with no any errors:aplay --buffer-size=32768 --period-size=4096 /usr/share/sounds/alsa/Front_Center.wav
.
- For instance, the following buffer/period size settings on
- As some unknown issues in guest Linux OS (confirmed in v6.7 and v6.12), you need
to adjust the buffer size to more than four times of period size, or
the program cannot write the PCM frames into guest OS ALSA stack.
Device Tree compiler (dtc) is required. To install it on Debian/Ubuntu Linux, enter the following command:
$ sudo apt install device-tree-compiler
For macOS, use the following command:
$ brew install dtc
For demonstration purposes, ext4 is used for file system mounting.
ext4
is a native Linux filesystem, offering stability, high capacity, reliability,
and performance while requiring minimal maintenance. The mkfs.ext4
command can
create an ext4 file system from disk partitions. This command is a symbolic link of
the mke2fs command, and its
usage is the same as the mke2fs command.
For most GNU/Linux distributions, mkfs.ext4
command should be installed in advance.
For macOS, use the following command:
$ brew install e2fsprogs
Build the emulator:
$ make
Download prebuilt Linux kernel image:
$ make check
Please be patient while semu
is running.
Reference output:
Starting syslogd: OK
Starting klogd: OK
Running sysctl: OK
Starting network: OK
Welcome to Buildroot
buildroot login:
Enter root
to access shell.
You can exit the emulator using: <Ctrl-a x>. (press Ctrl+A, leave it, afterwards press X)
./semu -k linux-image [-b dtb-file] [-i initrd-image] [-d disk-image]
linux-image
is the path to the Linux kernelImage
.dtb-file
is optional, as it specifies the user-specified device tree blob.initrd-image
is optional, as it specifies the user-specified initial RAM disk image.disk-image
is optional, as it specifies the path of a disk image in ext4 file system for the virtio-blk device.
An automated build script is provided to compile the RISC-V cross-compiler, Busybox, and Linux kernel from source. Please note that it only supports the Linux host environment.
$ make build-image
semu
is released under the MIT License.
Use of this source code is governed by a MIT-style license that can be found in the LICENSE file.