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

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

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

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

F9 Microkernel code reading - part 1

F9 Microkernel code reading - part 1

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F9 Microkernel code reading - part 1