1. EMBEDDED LINUX #2

2. CONTENTS
Boot sequence
BLOB
start.S
trampoline.S
main.c

3. Boot sequence (1/3) Boot sequence of common linux POWER ON ROM BIOS
BOOT LOADER
MBR
BOOT SECTOR
KERNEL LOAD & EXECUTION
BOOT PROGRAM

4. Boot sequence (2/3) Boot sequence of embedded linux POWER ON BLOB
UNCOMPRESS
zImage
piggy.o
KERNEL EXECUTION

5. Boot sequence (3/3) Flow 9 KERNEL START POWER ON 1 8
Jump to decompressed
kernel and execution
Jump to 0x
(flash memory area) 2
Decompress
kernel image (piggy.o) 7 3
Execution
Copy zImage to
sdram area 6 ※
BLOB
(boot loader) 4 5
Conditional jump A
Command mode

6. BLOB (1/16) Functions Hardware initialization Kernel booting
Download host sides kernel or ramdisk image into sdram
Write downloaded kernel or ramdisk image into flash memory

7. BLOB (2/16) Flow start.S main.c -> main() Auto boot Manual boot
Hardware initialization
Serial, timer initialization
Load kernel and ramdisk to sdram
main.c -> main()
Wait for 10 seconds
Wait for key press
Key pressed within 10 seconds
Auto boot
Manual boot
Run command
Get command()
BootKernel()
BootKernel()
SetClock()
Download() …

8. BLOB – start.S (3/16) Hardware initialization
Set exception vector table
Switch CPU to correct speed
Setup memory
LED initialization
Memory test
Relocate the second stage loader
Setup stack pointer

9. BLOB – start.S (4/16) _start() function (1/4) Memory location
0x1FFFFFFF
main()
_trampoline()
_start() 0x 0x

10. BLOB – start.S (5/16) _start() function (2/4) Flow Set exception
vector table 1 2
Define constants
Jump to reset()
function 3

11. BLOB – start.S (6/16) _start() function (3/4)
Set exception vector table
_start:
b reset
b undefined_instruction
b software_interrupt
b prefetch_abort
b data_abort
b not_used
b irq
b fiq
Exception
vector
table 0x 0x

12. BLOB – start.S (7/16) _start() function (4/4) Memory map 0xFFFFFFFF
Sdram banks
Registers
Flash banks
0xE
0xC 0x 0x 0x

13. BLOB – start.S (8/16) reset() function Flow Jump to the Second stage
loader (_trampoline()) 8
Disable all
interrupts 1
Switch CPU to
correct speed 2 7
Setup stack
pointer
Relocate the
second stage
loader
Setup memory 3 6 no
yes
LED
initialization 4 5 A
Wake-up
Sleep?

14. BLOB – trampoline.S (9/16) Infinite loop Call main() function
If main() ever returns, call it again

15. BLOB – trampoline.S (10/16) _trampoline() function (1/2)
Memory location
0xDFFFFFFF
0x1FFFFFFF
main()
_trampoline()
main()
_trampoline()
_start() 0x
0xC 0x

16. BLOB – trampoline.S (11/16) _trampoline() function (2/2) Flow
Call main()
function 1 2
Return ?

17. BLOB – main.c (12/16) Core routine of BLOB Serial initialization
Timer initialization
Load BLOB, kernel and ramdisk into sdram
Processing user-input command

18. BLOB – main.c (13/16) main() function (1/4) Memory location 0xDFFFFFFF
0x1FFFFFFF
main()
_trampoline()
main()
_trampoline()
_start() 0x
0xC 0x

19. BLOB – main.c (14/16) main() function (2/4) Flow Serial initialization7
Call boot_linux()
function 8
Wait for user
command
Timer
initialization 2 9
Processing
user command
yes
conditional
return no
Usable memory
check 3 6
Key pressed within
10 seconds?
Reload BLOB,
kernel and
ramdisk 4 5
Wait for key press
10sec

20. BLOB – main.c (15/16) main() function (3/4)
Memory location after reload
0xDFFFFFFF
0xC0FFFFFF
Ramdisk
Kernel
BLOB
main()
_trampoline()
0xC134FFFF
0xC10D0000
0xC
0xC
0xC

21. BLOB – main.c (16/16) main() function (4/4) User command
boot, clock, download
flash, help, reblob
reboot, reload, reset
speed, status

22. EMBEDDED LINUX #2 E N D [참고문헌] Chul, Park – StrongARM(SA1110)을 이용한
board level porting 작업
- 임베디드 리눅스 강좌