QEMU for ARM supports a special ‘virt’ machine designed for emulation and virtualization purposes. This document describes how to run U-Boot under it. Both 32-bit ARM and AArch64 are supported.

The ‘virt’ platform provides the following as the basic functionality:

  • A freely configurable amount of CPU cores
  • U-Boot loaded and executing in the emulated flash at address 0x0
  • A generated device tree blob placed at the start of RAM
  • A freely configurable amount of RAM, described by the DTB
  • A PL011 serial port, discoverable via the DTB
  • An ARMv7/ARMv8 architected timer
  • PSCI for rebooting the system
  • A generic ECAM-based PCI host controller, discoverable via the DTB

Additionally, a number of optional peripherals can be added to the PCI bus.

Building U-Boot

Set the CROSS_COMPILE environment variable as usual, and run:

  • For ARM:

    make qemu_arm_defconfig
  • For AArch64:

    make qemu_arm64_defconfig

Running U-Boot

The minimal QEMU command line to get U-Boot up and running is:

  • For ARM:

    qemu-system-arm -machine virt -bios u-boot.bin
  • For AArch64:

    qemu-system-aarch64 -machine virt -cpu cortex-a57 -bios u-boot.bin

Note that for some odd reason qemu-system-aarch64 needs to be explicitly told to use a 64-bit CPU or it will boot in 32-bit mode.

Additional persistent U-boot environment support can be added as follows:

  • Create envstore.img using qemu-img:

    qemu-img create -f raw envstore.img 64M
  • Add a pflash drive parameter to the command line:

    -drive if=pflash,format=raw,index=1,file=envstore.img

Additional peripherals that have been tested to work in both U-Boot and Linux can be enabled with the following command line parameters:

  • To add a Serial ATA disk via an Intel ICH9 AHCI controller, pass e.g.:

    -drive if=none,file=disk.img,id=mydisk -device ich9-ahci,id=ahci -device ide-drive,drive=mydisk,bus=ahci.0
  • To add an Intel E1000 network adapter, pass e.g.:

    -netdev user,id=net0 -device e1000,netdev=net0
  • To add an EHCI-compliant USB host controller, pass e.g.:

    -device usb-ehci,id=ehci
  • To add a NVMe disk, pass e.g.:

    -drive if=none,file=disk.img,id=mydisk -device nvme,drive=mydisk,serial=foo

These have been tested in QEMU 2.9.0 but should work in at least 2.5.0 as well.

Debug UART

The debug UART on the ARM virt board uses these settings: