kernel

bolthur/kernel project. Copyright (C) 2018 - 2025 bolthur project

Supported platforms

There are no completely supported platforms yet.

Planned support

Currently, the following targets are planned to be supported:

Broadcom SoC

• armv6 ( 32 bit )

  • RPI A
  • RPI A+
  • RPI B
  • RPI B+
  • RPI zero 1

• armv7-a ( 32 bit )

  • RPI 2B r.1

• armv8-a ( 64 bit - rpi 2 r.2, rpi 3 and rpi 4 series )

  • RPI 2B r.2
  • RPI 3B
  • RPI 3B+
  • RPI 4
  • RPI zero 2

List of real hardware for testing

• Raspberry PI 2 Model B ( rev 1.1 )
• Raspberry PI 3 Model B
• Raspberry PI Zero W

Building the project

Autotools related

Initial necessary command after checkout or adding new files autotools executed within project root:

autoreconf -iv

Configuring

mkdir build
cd build
### configure with one of the following commands
../configure --host arm-raspbi2b_r1-bolthur-eabi --enable-device=raspi2b_r1 --enable-debug --enable-output
../configure --host arm-raspi0_1-bolthur-eabi --enable-device=raspi0_1 --enable-debug --enable-output

Possible additional parameters to --host and --enable-device:

• --with-debug-symbols enables remote debugging mode ( blocks --enable-release )
• --with-optimization-level=x sets optimization from default ( 2 ) to specified one ( ignored when --enable-release is set )
• --enable-output enables kernel output ( blocks --enable-remote-debug )
• --enable-output-mm-phys activate tty output of physical memory manager
• --enable-output-mm-virt activate tty output of virtual memory manager
• --enable-output-mm-heap activate tty output of kernel heap
• --enable-output-mm-shared activate tty output of shared memory
• --enable-output-mailbox activate tty output of mailbox implementation
• --enable-output-timer activate tty output of timer implementation
• --enable-output-initrd activate initrd implementation output
• --enable-output-event activate event implementation output
• --enable-output-process activate process implementation output
• --enable-output-interrupt activate interrupt request output
• --enable-output-exception activate exception handler output
• --enable-output-elf activate elf routine output
• --enable-output-syscall activate syscall output
• --enable-output-serial activate serial handling output
• --enable-output-message activate message system output
• --enable-output-rpc activate rpc system output
• --enable-output-ssp activate ssp origin output in kernel
• --enable-remote-debug activate remote debugging ( blocks --enable-output )
• --enable-release activate release build ( blocks --enable-debug and ignores --with-optimization-level )

Building

# just call make for building the project
make clean && make

Real hardware

Getting some debug-print on real hardware, like debug debug-print is done via serial. In case of raspberry pi it is UART0. So to get execution debug-print, you'll need an TTL-RS232 to USB convert cable. When that is existing, wire it up like on the following page and connect it to the development machine. The most simple way to get the serial debug-print is using screen with the connected usb to serial.

# Connect to usb tty port via screen
screen /dev/ttyUSB0 115200

# Exit tty screen session
Ctrl+a Shift+k y

Emulation

Emulation of the project with qemu during development is not recommended. The platforms itself are most time very limited or completely not supported. Raspberry pi is very limited and lack necessary features, also the n900 or the beagleboard are completely not supported. We recommend testing on real hardware with remote debugging via serial port.

Emulation of the kernel project with qemu during development may be done at all with the following commands. When kernel debugging is necessary, add the parameter shorthand -s -S or the long version -gdb tcp:1234 to qemu call:

# raspberry pi zero kernel emulation
qemu-system-arm -M raspi0 -cpu arm1176 -m 512M -no-reboot -serial stdio -kernel ./bolthur/kernel/target/raspi/kernel_qemu.img -initrd ../build-aux/platform/raspi/initrd -dtb ../config/dts/raspi/bcm2708-raspi-zero.dtb -drive file=../build-aux/platform/raspi/sdcard.img,format=raw -append "root=/dev/storage/sd1 rootfstype=ext2" -usb -device usb-mouse -device usb-kbd -s -S

# raspberry pi 2B rev 1 kernel emulation
qemu-system-arm -M raspi2b -cpu cortex-a7 -m 1G -no-reboot -serial stdio -kernel ./bolthur/kernel/target/raspi/kernel7_qemu.img -initrd ../build-aux/platform/raspi/initrd -dtb ../config/dts/raspi/bcm2709-raspi-2-b.dtb -drive file=../build-aux/platform/raspi/sdcard.img,format=raw -append "bcm2708_fb.fbwidth=1024 bcm2708_fb.fbheight=768 root=/dev/storage/sd1 rootfstype=ext2" -usb -device usb-mouse -device usb-kbd -s -S

# raspberry pi 3B kernel emulation
qemu-system-aarch64 -M raspi3b -cpu cortex-a53 -m 1G -no-reboot -serial stdio -kernel ./bolthur/kernel/target/raspi/kernel8_qemu.img -initrd ../build-aux/platform/raspi/initrd -dtb ../config/dts/raspi/bcm2710-raspi-3-b.dtb -drive file=../build-aux/platform/raspi/sdcard.img,format=raw -append "root=/dev/storage/sd1 rootfstype=ext2" -usb -device usb-mouse -device usb-kbd -s -S

Debugging

Within the project root there are two different gdbinit files that may be used for setting up the debugger. .gdbinit-qemu should be chosen, when debugging the kernel with qemu. In case you want to use remote debugging, you should choose .gdbinit-remote.

The files can be specified by using the parameter -x.

# qemu debugging example
/opt/bolthur/sysroot/arm/bin/arm-unknown-bolthur-eabi-gdb -x .gdbinit-qemu

# remote debugging example
/opt/bolthur/sysroot/arm/bin/arm-unknown-bolthur-eabi-gdb -x .gdbinit-remote

When starting remote debugging, you need to specify the target, e.g. target /dev/ttyUSB0 to connect to the running instance. Furthermore, you need to configure the project with option --enable-debug.