Awesome
Build a minimal multi-tasking OS kernel for ARM from scratch
Prerequisites
- QEMU with an STM32 microcontroller implementation
- Build instructions
./configure --disable-werror --enable-debug \
--target-list="arm-softmmu" \
--extra-cflags=-DSTM32_UART_NO_BAUD_DELAY \
--extra-cflags=-DSTM32_UART_ENABLE_OVERRUN \
--disable-gtk
make
- GNU Toolchain for ARM
- Set
$PATH
accordingly
Steps
00-Semihosting
- Minimal semihosted ARM Cortex-M "Hello World"
00-HelloWorld
- Enable STM32 USART to print trivial greetings
01-HelloWorld
- Almost identical to the previous one but improved startup routines
02-ContextSwitch-1
- Basic switch between user and kernel mode
03-ContextSwitch-2
- system call is introduced as an effective method to return to kernel
04-Multitasking
- Two user tasks are interatively switching
05-TimerInterrupt
- Enable SysTick for future scheduler implementation
06-Preemptive
- Basic preemptive scheduling
07-Threads
- Implement user-level threads
08-CMSIS
- Illustrate hardware abstraction layer (HAL) by introducing CMSIS
- Both emulator (based on stm32-p103) and real device (STM32F429i discovery) are supported.
Building and Verification
- Changes the current working directory to the specified one and then
make
make qemu
Guide to Hacking 08-CMSIS
08-CMSIS implements preemptive round-robin scheduling with user-level threads for STM32F429i-Discovery (real device) and STM32-P103 (qemu).
Get the dependencies:
git submodule init
git submodule update
Install additional utilities:
- If you would like to verify the kernel on STM32F29i-Discovery, you should install:
Quick Start / Support Devices:
- STM32F429i-Discovery(physical devices)
- Details in Chinese by NCKU
- STM32F429i-Discovery uses
USART1(Tx=PA9,Rx=PA10,baud rate=115200)
as default serial port here.- You would need a terminal emulator, such as
screen
- Installation on Ubuntu / Debian based systems:
sudo apt-get install screen
- Then, attach the device file where a serial to USB converter is attached:
screen /dev/ttyUSB0 115200 8n1
- Once you want to quit screen, press:
Ctrl-a
thenk
- Installation on Ubuntu / Debian based systems:
- You would need a terminal emulator, such as
Available commands:
Overall
make all
- Build all target's bin,elf,objdump files in the "release" directory.
- NOTE:
make
doe NOT equal tomake all
here because Makefile useseval
fortargets
.
make clean
- Remove the entire "release" directory.
STM32-P103(QEMU)
make p103
ormake target PLAT=p103
- Build "p103.bin"
make qemu
- Build "p103.bin" and run QEMU automatically.
make qemu_GDBstub
- Build "p103.bin" and run QEMU with GDB stub and wait for remote GDB automatically.
make qemu_GDBconnect
- Open remote GDB to connect to the QEMU GDB stub with port:1234 (the default port).
STM32F429i-Discovery(physical device)
make f429disco
ormake target PLAT=f429disco
- Build "f429disco.bin"
make st-flash
- Build "f429disco.bin" and flash the binary into STM32F429 with st-link.
make st-erase
- Sometimes, STM32F429i-Discovery will not be able to flash new binary file, then you will need to erase flash memory with st-link.
- Erase the entire flash on STM32F429.
make gdb_ST-UTIL
- Using GDB with ST-LINK on STM32F429.
- Remember to open another terminal,and type "st-util" to open "STLINK GDB Server"
Directory Tree:
- core
- Hardware independent source and header files.
- platform
- Hardware dependent source and header files.
- cmsis
- With cmsis,porting would be much easier!
- release
- This directory will be created after "Target" in Makefile is called.
- Containing the elf,bin,objdump files in corresponding directory.
make clean
will remove the entire directory,do not put personal files inside it!
Porting Guide:
You should know what CMSIS is and why it saves us a lot of efforts.
cmsis
is a submodule from TibaChang/cmsis, maintained by Jia-Rung Chang.
The full project can be divided into two layer:
- hardware-dependent part (HAL)
- "platform" directory
- hardware-indepentent part
- "core" directory
Steps to launch the kernel on real devices:
STEP 1
Select a target name for your device, such as f429disco
.
In this guide, we assume its name is example_device
with vendor name "f429disco".
Create example_device
directory in "platform" and f429disco
directory in "cmsis" directory.
Create "include" and "src" directory in platform/example_device/
STEP 2
Introducing your CMSIS for your target, where it should be in the mbed repo.
For example, the CMSIS for STM32F429i-discovery could be found here.
We only need ".h" files, do not copy any ".c" files.
Put the header files into cmsis/f429discoexample_device
.
cmsis is a submodule in this project, maintianed by Tiba Chang.
NOTE:
You may encounter some error messages during building binary for your target.
You need to solve it mannually.
Usually, some files may be missing caused by some specific "define".
You could just comment out that definition to resolve this problem.
STEP 3
This is the most difficult part.
You have to implement the files in platform/example_device/include/
and
platform/example_device/src/
.
According to different device vendor(such as STMicroelectronics, NXP, etc), the implementation is very different.
Please look into the current example:f429disco
,and you will figure it out!
The function interface must be as same as the function interface in "platform/STM32F429/inc/" due to this is HAL for the entire project.
STEP 4
Add your target rules into Makefile.
Please look the example f429disco
in the Makefile.
Most of the rules are reusable,so all you need is copy-n-paste, modifying the variable/target name and knowing what gcc arguments suit your target!
rules.mk
- You should
NOT
modify this file! - All of the rules are encapsulated into macro, used inMakefile
.
- You should
Makefile
:- If your device vendor name does not exist, create new variable and
assign a name to it!
- E.g.
STM32 := STM32
- E.g.
- Add your device name
- E.g.
STM32F429_DEVICE := f429disco
- E.g.
- Check your device CPU type(Cortex-M3/4)
- In
target_using_CM4_list
- In
- Will you use CMSIS?
- If NOT,add to
target_NOT_using_CMSIS_list
- If NOT,add to
- Use the predefined macro to produce the corresponding directory and
device specific variable(device name,vendor name)
- E.g.
$(eval $(call eval_all_variable,$(STM32F429_DEVICE),$(STM32)))
- The
vendor name
is used in thecmsis
directory name. They must be associated with each other.
- E.g.
- Use the predefined macro to produce the corresponding GCC commands
- E.g.:
$(eval $(call eval_build_command,$(STM32F429_DEVICE)))
- This will derive lots of variables that you don't see in the
Makefile
.
- E.g.:
- Add your device name to
all
- In the specific form:
$($(YOUR_DEVICE_NAME)_TARGET)
, this variable will be automatic derived byrules.mk
- E.g.:
$($(STM32F429_DEVICE)_TARGET)
- In the specific form:
- If your device vendor name does not exist, create new variable and
assign a name to it!
STEP 5
Congratulations!
Now, you can try the "Available commands" in this README.
Licensing
mini-arm-os
is freely redistributable under the two-clause BSD License.
Use of this source code is governed by a BSD-style license that can be found
in the LICENSE
file.