OpenRISC System emulator
QEMU can emulate 32-bit OpenRISC CPUs using the qemu-system-or1k executable.
OpenRISC CPUs are generally built into “system-on-chip” (SoC) designs that run on FPGAs. These SoCs are based on the same core architecture as the or1ksim (the original OpenRISC instruction level simulator) which QEMU supports. For this reason QEMU does not need to support many different boards to support the OpenRISC hardware ecosystem.
The OpenRISC CPU supported by QEMU is the or1200, it supports an MMU and can
run linux.
Choosing a board model
For QEMU’s OpenRISC system emulation, you must specify which board model you
want to use with the -M or --machine option; the default machine is
or1k-sim.
If you intend to boot Linux, it is possible to have a single kernel image that will boot on any of the QEMU machines. To do this one would compile all required drivers into the kernel. This is possible because QEMU will create a device tree structure that describes the QEMU machine and pass a pointer to the structure to the kernel. The kernel can then use this to configure itself for the machine.
However, typically users will have specific firmware images for a specific machine.
If you already have a system image or a kernel that works on hardware and you
want to boot with QEMU, check whether QEMU lists that machine in its -machine
help output. If it is listed, then you can probably use that board model. If
it is not listed, then unfortunately your image will almost certainly not boot
on QEMU. (You might be able to extract the filesystem and use that with a
different kernel which boots on a system that QEMU does emulate.)
If you don’t care about reproducing the idiosyncrasies of a particular
bit of hardware, such as small amount of RAM, no PCI or other hard disk, etc.,
and just want to run Linux, the best option is to use the virt board. This
is a platform which doesn’t correspond to any real hardware and is designed for
use in virtual machines. You’ll need to compile Linux with a suitable
configuration for running on the virt board. virt supports PCI, virtio
and large amounts of RAM.