F9 Microkernel code reading - part 1
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The document provides an overview and agenda for code reading and tracing of the F9 microkernel. It begins with an overview of the F9 microkernel, its characteristics and design for ARM Cortex-M processors. It then discusses using cscope and ctags for code navigation and demonstrates the kernel entry point and initial startup routines. Finally, it prepares the environment for remote debugging the kernel using st-link and gdb.
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F9 Microkernel code reading - part 1
- 1. Part 1 : Code Reading of F9 Microkernel ben6 2013-‐10-‐16
- 2. F9 Agenda • Overview of F9-‐Microkernel • Code reading (cscope, ctags) • Code trace
- 3. F9 Agenda • Overview of F9-‐Microkernel • Code reading (cscope, ctags) • Code trace
- 4. F9 Microkernel Overview • an experimental microkernel used to construct flexible embedded systems inspired by famous L4 microkernel. • The moMvaMon of F9 microkernel is to deploy modern kernel techniques to support – running real-‐Mme and Mme-‐sharing applicaMons (ex: wireless communicaMons) for ARM Cortex-‐M series microprocessors with efficiency (performance + power consumpMon) – security (memory protecMon + isolated execuMon)
- 5. CharacterisMcs • F9 follows the fundamental principles of microkernels in that it implements address spaces, thread management, and IPC only in the privileged kernel. • Designed and customized for ARM Cortex-‐M, supporMng NVIC (Nested Vectored Interrupt Controller), Bit Banding, MPU (Memory ProtecMon Unit) • Energy efficient scheduling and Mckless Mmer • KProbes • Independent TCB (Thread Control Block) for each thread with its global ID
- 6. CharacterisMcs (Cont.) • Memory management – Memory pool, Flexible page, Address space • System calls: – Grant, Map, Flush • UTCB concept – a small thread-‐specific region in the thread's virtual address space, which is always mapped • Synchronous IPC • Debugging and profiling mechanisms
- 7. F9 Agenda • Overview of F9-‐Microkernel • Code reading (cscope, ctags) • Code trace
- 8. Kernel Line of code Kernel C code line: 2661 Git head: 7ae6e15bdf4d67740ef9fa2a0c6a2a194df9553b
- 9. cscope • CTRL-‐D to quit • Use arrow key <up>, <down> to select • Type symbol name your want to search
- 10. Use case of cscope 1. 2. 3. 4. 5. Get f9-‐kernel source code git clone h=ps://github.com/f9micro/f9-‐kernel Generate cscope.files to be scanned – cd f9-‐kernel; find . -‐name "*.c" -‐o -‐name "*.h" > cscope.files Generate Cscope database cscope -‐b -‐q -‐k Using the database – default Cscope browser cscope -‐d (be able to use vim or other editor support cscope database) RegeneraHng database when source code changes – Use same command step 4. Reference: hhp://cscope.sourceforge.net/large_projects.html
- 11. vim + ctags • sudo apt-‐get install ctags • Generate tags ctags –R * • key definiMon at vim CTRL + ] è goto the funcMon definiMon CTRL + t è back to previous funcMon call
- 12. PART 1 F9 KERNEL ENTRY
- 13. F9-‐kernel Entry • plamorm/f9.ld è F9 ldscript __l4_start
- 14. F9-‐kernel Entry • plamorm/f9.ld Header of f9.bin is isr_vector table for Cortex-‐M MCU
- 15. f9-‐kernel: __l4_start kernel/init.c • Be reset handler • F9 startup entry
- 16. __l4_start • IniMal hooks • Copy data segment for 1st iniMalizaMon • Clear segments • IniMalize system clock • Call main() entry
- 17. start.c : main.c • IniMal for level plamorm hooks • Irq iniMal and disable interrupt • Setup FloaMng Point Unit • Show banner • IniMal for Level kernel hooks • Create and idle and root thread • Create Mmer 64 Mcks for delivering ipc • Init LAST stage hooks • Switch to iniMal kernel thread
- 18. Enable/disable irq inline assembly Syntax: __asm__ __volaMle__("InstrucMon List"); • __volaMle__ Tell gcc don’t change my intrusMon list • cpsid, cpsie reference: Implemented interrupt enabling delay in the Cortex-‐M3 and Cortex-‐M4 processors
- 19. kMmer_event_create • kMmer.c • Create new event entry • add to linked list of event table • Add entry for event scheduling
- 20. Switch to kernel • Create kernel thread and enable running by context switch
- 21. F9 Agenda • Overview of F9-‐Microkernel • Code reading (cscope, ctags) • Code trace
- 22. Console setup before code trace Pl2303 console with STM32F4 • USB2TTL RX (white) -‐-‐-‐> PA0 • USB2TTL TX (green) -‐-‐-‐> PA1 USB-‐Serial Controller Prolific 2303
- 23. Toolchain for Cortex-‐M4 • Sourcery CodeBench – ARM Processors: EABI Release – Verified versions: arm-‐2012.03, arm-‐2013.05 • GNU Tools for ARM Embedded Processors
- 24. stlink Project for tools we used: st-‐ flash, st-‐uMl hhps://github.com/texane/stlink
- 25. Code trace: st-‐uMl Remote debug port for gdb
- 26. Code trace: gdb remote target remote :4242
- 27. Code trace issue • Debug Panic Git HEAD: 7ae6e15bdf4d67740ef9fa2a0c6a2a194df9553b
- 28. Discussions F9 ?
- 29. References • F9 Microkernel source code and introducMon • Using Cscope on large projects (example: the Linux kernel) • Ctags wiki • __asm__ __volaMle__ GCC的内嵌汇编语法 AT&T汇编语⾔言语法（⼀一） • Implemented interrupt enabling delay in the Cortex-‐M3 and Cortex-‐M4 processors • texane's stlink project at github