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63 lines
2.7 KiB
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63 lines
2.7 KiB
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.. _RISC-V-System-emulator:
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RISC-V System emulator
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======================
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QEMU can emulate both 32-bit and 64-bit RISC-V CPUs. Use the
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``qemu-system-riscv64`` executable to simulate a 64-bit RISC-V machine,
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``qemu-system-riscv32`` executable to simulate a 32-bit RISC-V machine.
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QEMU has generally good support for RISC-V guests. It has support for
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several different machines. The reason we support so many is that
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RISC-V hardware is much more widely varying than x86 hardware. RISC-V
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CPUs are generally built into "system-on-chip" (SoC) designs created by
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many different companies with different devices, and these SoCs are
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then built into machines which can vary still further even if they use
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the same SoC.
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For most boards the CPU type is fixed (matching what the hardware has),
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so typically you don't need to specify the CPU type by hand, except for
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special cases like the ``virt`` board.
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Choosing a board model
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----------------------
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For QEMU's RISC-V system emulation, you must specify which board
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model you want to use with the ``-M`` or ``--machine`` option;
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there is no default.
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Because RISC-V systems differ so much and in fundamental ways, typically
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operating system or firmware images intended to run on one machine
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will not run at all on any other. This is often surprising for new
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users who are used to the x86 world where every system looks like a
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standard PC. (Once the kernel has booted, most user space software
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cares much less about the detail of the hardware.)
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If you already have a system image or a kernel that works on hardware
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and you want to boot with QEMU, check whether QEMU lists that machine
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in its ``-machine help`` output. If it is listed, then you can probably
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use that board model. If it is not listed, then unfortunately your image
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will almost certainly not boot on QEMU. (You might be able to
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extract the file system and use that with a different kernel which
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boots on a system that QEMU does emulate.)
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If you don't care about reproducing the idiosyncrasies of a particular
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bit of hardware, such as small amount of RAM, no PCI or other hard
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disk, etc., and just want to run Linux, the best option is to use the
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``virt`` board. This is a platform which doesn't correspond to any
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real hardware and is designed for use in virtual machines. You'll
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need to compile Linux with a suitable configuration for running on
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the ``virt`` board. ``virt`` supports PCI, virtio, recent CPUs and
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large amounts of RAM. It also supports 64-bit CPUs.
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Board-specific documentation
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----------------------------
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Unfortunately many of the RISC-V boards QEMU supports are currently
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undocumented; you can get a complete list by running
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``qemu-system-riscv64 --machine help``, or
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``qemu-system-riscv32 --machine help``.
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RISC-V CPU features
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-------------------
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