BSP Supporting QEMU's PReP Emulation

As of rtems-4.11 two variants of the 'motorola_powerpc' BSP family are available:

  • qemuprep
  • qemuprep-altivec

The most significant differences between the emulation and real PREP hardware are

  • no OpenPIC, just a 8259 PIC (even though qemu implements an openpic at least to some extent it is not configured into the prep platform as of qemu-0.14.1).
  • no VME (absense of the VME controller is detected by the BSP)
  • the only network chip supported by both, qemu and vanilla RTEMS is the ISA NE2000 controller. Note that the default interrupt line settings used by RTEMS and QEMU differ: RTEMS uses 5 and QEMU 9. This can be addressed by passing a RTEMS commandline option --ne2k-irq=9. Other controllers (i8559, e1000, pcnet) implemented by qemu can also be used but require unbundled RTEMS drivers (libbsdport). Note that the bundled 'if_fxp' has not been ported to PPC and works on x86 only.
  • unlike a real motorola board you can run qemu emulating a 7400 CPU which features altivec. I.e., you can use this BSP (altivec-enabled variant) to test altivec-enabled code.


qemu had quite a few bugs related to the PREP platform. Version 0.12.4, for example, required patches. 0.14.1 seems to have fixed the show-stoppers. Hence, you need at least qemu-0.14.1 for this BSP; it should work without the need for patching QEMU.


Qemu requires you to use a BIOS/firmware. The one that came with qemu 0.12.4 didn't work for me so I created a minimal dummy that provides enough functionality for the RTEMS bootloader to work.

BSP Variants

You can compile the BSP for either a 604 CPU or a 7400 (altivec-enabled). Note that you cannot run the altivec-enabled BSP variant on a CPU w/o altivec/SIMD hardware. The non-altivec variant is called 'qemuprep' and the altivec-enabled one 'qemuprep-altivec'. Hence, you can configure RTEMS:

604/non-altivec variant only:
  configure --target=powerpc-rtems --enable-rtemsbsp=qemuprep
7400/altivec variant only:
  configure --target=powerpc-rtems --enable-rtemsbsp=qemuprep-altivec
both variants:
  configure --target=powerpc-rtems --enable-rtemsbsp='qemuprep qemuprep-altivec'

Building QEMU

In case you have no pre-built qemu-0.14.1 you can compile it yourself:

cd qemu-0.14.1
configure --target-list=ppc-softmmu

Running QEMU

A number of command-line options are important (BTW: make sure you run the PPC/PREP emulator and not a natively installed i386/PC emulating 'qemu')

-M prep         --- select machine type: prep
-cpu 604        --- select 604 CPU for non-altivec variant
-cpu 7400       --- select 7400 CPU for altivec variant

              NOTE: the 7455 and 7457 emulations are buggy as of
              qemu-0.14.1 and they won't work.

-bios <rtems-install-prefix>/powerpc-rtems/qemuprep/qemu_fakerom.bin
-bios <rtems-install-prefix>/powerpc-rtems/qemuprep-altivec/qemu_fakerom.bin
                --- select proprietary dummy 'BIOS'

-nographic      --- redirect serial/IO to console where qemu is run

-kernel <path>  --- path to your RTEMS executable (.ralf file, e.g., 'hello.ralf')
-no-reboot      --- terminate after one run
-append <arg>   --- RTEMS kernel comand line (use e.g., to modify
                    ne2000 driver interrupt line)


(We assume your RTEMS application is correctly configured and built for networking using the ne2k adapter [other adapters can be used with unbundled/libbsdport drivers])

I use networking with a 'tap' interface on the host machine and can then communicate with the emulated target in any desired way.

On (linux) host:

# create a 'permanent' tap device that can be used by myself
# (as non-root user).
sudo tunctl -u `id -u`
# configure tap0 interface
sudo ifconfig tap0 netmask up
# provide a suitable dhcpd config file (for the emulated
# platform to boot: IP address etc.
# execute dhcp on host
sudo dhcpd -d tap0

Start emulated prep platform:

ppc-softmmu/qemu-system-ppc                               \
    -M prep                                               \
    -cpu 7400                                             \
    -bios  <rtems-prefix>/powerpc-rtems/qemuprep-altivec/lib/qemu_fakerom.bin \
    -kernel <my_path>/my_app.ralf                         \
	-append --ne2k-irq=9                                  \
    -nographic                                            \
    -no-reboot                                            \
    -net nic,model=ne2k_isa                               \
    -net tap,vlan=0,ifname=tap0,script=no,downscript=no 

Again: if you use the non-altivec BSP variant, use -cpu 604 and if you use the altivec-enabled variant then you MUST use -cpu 7400.


  1. Developer/Simulators/QEMU
  3. QEMU
Last modified on Mar 10, 2015 at 11:46:33 PM Last modified on Mar 10, 2015, 11:46:33 PM