This BSP offers only one variant,
amd64. The BSP can run on UEFI-capable
systems by using FreeBSD’s bootloader, which then loads the RTEMS executable (an
Currently only the console driver and context initialization and switching are
functional (to a bare minimum), but this is enough to run the
in the RTEMS testsuite.
184.108.40.206. Build Configuration Options¶
There are no options available to
configure at build time, at the moment.
220.127.116.11. Testing with QEMU¶
To test with QEMU, we need to:
- Build / install QEMU (most distributions should have it available on the package manager).
- Build UEFI firmware that QEMU can use to simulate an x86-64 system capable of
booting a UEFI-aware kernel, through the
18.104.22.168.1. Building TianoCore’s UEFI firmware, OVMF¶
Complete detailed instructions are available at TianoCore’s Github’s wiki.
Quick instructions (which may fall out of date) are:
$ git clone git://github.com/tianocore/edk2.git $ cd edk2 $ make -C BaseTools $ . edksetup.sh
Conf/target.txt to set:
ACTIVE_PLATFORM = OvmfPkg/OvmfPkgX64.dsc TARGET = DEBUG TARGET_ARCH = X64 # You can use GCC46 as well, if you'd prefer TOOL_CHAIN_TAG = GCC5
build in the
edk2 directory - the output should list the
location of the
OVMF.fd file, which can be used with QEMU to boot into a UEFI
You can find the
OVMF.fd file like this as well in the edk2 directory:
$ find . -name "*.fd" ./Build/OvmfX64/DEBUG_GCC5/FV/MEMFD.fd ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF.fd # the file we're looking for ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_CODE.fd ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_VARS.fd
22.214.171.124. Boot RTEMS via FreeBSD’s bootloader¶
The RTEMS executable produced (an ELF file) needs to be placed in the FreeBSD’s
To do that, we first need a hard-disk image with FreeBSD installed on it. Download FreeBSD’s installer “memstick” image for amd64 and then run the following commands, replacing paths as appropriate.
$ qemu-img create freebsd.img 8G $ OVMF_LOCATION=/path/to/ovmf/OVMF.fd $ FREEBSD_MEMSTICK=/path/to/FreeBSD-11.2-amd64-memstick.img $ qemu-system-x86_64 -m 1024 -serial stdio --bios $OVMF_LOCATION \ -drive format=raw,file=freebsd.img \ -drive format=raw,file=$FREEBSD_MEMSTICK
The first time you do this, continue through and install FreeBSD. FreeBSD’s installation guide may prove useful if required.
Once installed, build your RTEMS executable (an ELF file), for
hello.exe. We need to transfer this executable into
filesystem, at either
elsewhere, if you don’t mind user FreeBSD’s
loader’s prompt to boot your
If your host system supports mounting UFS filesystems as read-write (eg. FreeBSD), go ahead and:
- Within the filesystem, back the existing FreeBSD kernel up (i.e. effectively
cp -r /boot/kernel /boot/kernel.old).
- Place your RTEMS executable at
If your host doesn’t support mounting UFS filesystems (eg. most Linux kernels), do something to the effect of the following.
On the host
# Upload hello.exe anywhere accessible within the host $ curl --upload-file hello.exe https://transfer.sh/rtems
Then on the guest (FreeBSD), login with
# Back the FreeBSD kernel up $ cp -r /boot/kernel/ /boot/kernel.old # Bring networking online if it isn't already $ dhclient em0 # You may need to add the --no-verify-peer depending on your server $ fetch https://host.com/path/to/rtems/hello.exe # Replace default kernel $ cp hello.exe /boot/kernel/kernel $ reboot
After rebooting, the RTEMS kernel should run after the UEFI firmware and
FreeBSD’s bootloader. The
-serial stdio QEMU flag will let the RTEMS console
send its output to the host’s
During the BSP’s initialization, the paging tables are setup to identity-map the first 512GiB, i.e. virtual addresses are the same as physical addresses for the first 512GiB.
The page structures are set up statically with 1GiB super-pages.
Page-faults are not handled.
RAM size is not detected dynamically and defaults to 1GiB, if the
RamSize parameter is not used.
126.96.36.199. Interrupt Setup¶
32 (i.e. 33 interrupt vectors in total) are
setup as “RTEMS interrupts”, which can be hooked through
The Interrupt Descriptor Table supports a total of 256 possible vectors (0
through 255), which leaves a lot of room for “raw interrupts”, which can be
Since the APIC needs to be used for the clock driver, the PIC is remapped (IRQ0 of the PIC is redirected to vector 32, and so on), and then all interrupts are masked to disable the PIC. In this state, the PIC may _still_ produce spurious interrupts (IRQ7 and IRQ15, redirected to vector 39 and vector 47 respectively).
The clock driver triggers the initialization of the APIC and then the APIC timer.
The I/O APIC is not supported at the moment.
IRQ32 is reserved by default for the APIC timer (see following section).
IRQ255 is reserved by default for the APIC’s spurious vector.
Besides the first 33 vectors (0 through 32), and vector 255 (the APIC spurious vector), no other handlers are attached by default.
188.8.131.52. Clock Driver¶
The clock driver currently uses the APIC timer. Since the APIC timer runs at the
CPU bus frequency, which can’t be detected easily, the PIT is used to calibrate
the APIC timer, and then the APIC timer is enabled in periodic mode, with the
initial counter setup such that interrupts fire at the same frequency as the
clock tick frequency, as requested by
184.108.40.206. Console Driver¶
The console driver defaults to using the
COM1 UART port (at I/O port
0x3F8), using the
NS16550 polled driver.