From d6d98968142f9c2541ee28e239d6a95b117499da Mon Sep 17 00:00:00 2001 From: Bin Meng Date: Tue, 26 Jan 2021 14:00:06 +0800 Subject: [PATCH] docs/system: Add RISC-V documentation Add RISC-V system emulator documentation for generic information. `Board-specific documentation` and `RISC-V CPU features` are only a placeholder and will be added in the future. Signed-off-by: Bin Meng Reviewed-by: Alistair Francis Message-id: 20210126060007.12904-9-bmeng.cn@gmail.com Signed-off-by: Alistair Francis --- docs/system/target-riscv.rst | 62 ++++++++++++++++++++++++++++++++++++ docs/system/targets.rst | 1 + 2 files changed, 63 insertions(+) create mode 100644 docs/system/target-riscv.rst diff --git a/docs/system/target-riscv.rst b/docs/system/target-riscv.rst new file mode 100644 index 0000000000..9f4b7586e5 --- /dev/null +++ b/docs/system/target-riscv.rst @@ -0,0 +1,62 @@ +.. _RISC-V-System-emulator: + +RISC-V System emulator +====================== + +QEMU can emulate both 32-bit and 64-bit RISC-V CPUs. Use the +``qemu-system-riscv64`` executable to simulate a 64-bit RISC-V machine, +``qemu-system-riscv32`` executable to simulate a 32-bit RISC-V machine. + +QEMU has generally good support for RISC-V guests. It has support for +several different machines. The reason we support so many is that +RISC-V hardware is much more widely varying than x86 hardware. RISC-V +CPUs are generally built into "system-on-chip" (SoC) designs created by +many different companies with different devices, and these SoCs are +then built into machines which can vary still further even if they use +the same SoC. + +For most boards the CPU type is fixed (matching what the hardware has), +so typically you don't need to specify the CPU type by hand, except for +special cases like the ``virt`` board. + +Choosing a board model +---------------------- + +For QEMU's RISC-V system emulation, you must specify which board +model you want to use with the ``-M`` or ``--machine`` option; +there is no default. + +Because RISC-V systems differ so much and in fundamental ways, typically +operating system or firmware images intended to run on one machine +will not run at all on any other. This is often surprising for new +users who are used to the x86 world where every system looks like a +standard PC. (Once the kernel has booted, most user space software +cares much less about the detail of the hardware.) + +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 file system 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, recent CPUs and +large amounts of RAM. It also supports 64-bit CPUs. + +Board-specific documentation +---------------------------- + +Unfortunately many of the RISC-V boards QEMU supports are currently +undocumented; you can get a complete list by running +``qemu-system-riscv64 --machine help``, or +``qemu-system-riscv32 --machine help``. + +RISC-V CPU features +------------------- diff --git a/docs/system/targets.rst b/docs/system/targets.rst index 564cea9a9b..75ed1087fd 100644 --- a/docs/system/targets.rst +++ b/docs/system/targets.rst @@ -19,6 +19,7 @@ Contents: target-m68k target-mips target-ppc + target-riscv target-rx target-s390x target-sparc