EMBEDDED LINUX #2

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

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

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

Boot sequence (3/3) Flow 9 KERNEL START POWER ON 1 8 Jump to decompressed kernel and execution Jump to 0x00000000 (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

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

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() …

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

BLOB – start.S (4/16) _start() function (1/4) Memory location 0x1FFFFFFF main() _trampoline() _start() 0x00000400 0x00000000

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

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 0x00000004 0x00000000

BLOB – start.S (7/16) _start() function (4/4) Memory map 0xFFFFFFFF Sdram banks Registers Flash banks 0xE0000000 0xC0000000 0x20000000 0x80000000 0x00000000

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?

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

BLOB – trampoline.S (10/16) _trampoline() function (1/2) Memory location 0xDFFFFFFF 0x1FFFFFFF main() _trampoline() main() _trampoline() _start() 0x00000400 0xC0000400 0x00000000

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

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

BLOB – main.c (13/16) main() function (1/4) Memory location 0xDFFFFFFF 0x1FFFFFFF main() _trampoline() main() _trampoline() _start() 0x00000400 0xC0000400 0x00000000

BLOB – main.c (14/16) main() function (2/4) Flow Serial initialization 7 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

BLOB – main.c (15/16) main() function (3/4) Memory location after reload 0xDFFFFFFF 0xC0FFFFFF Ramdisk Kernel BLOB main() _trampoline() 0xC134FFFF 0xC10D0000 0xC1010000 0xC1000000 0xC0000400

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

EMBEDDED LINUX #2 E N D [참고문헌] Chul, Park – StrongARM(SA1110)을 이용한 board level porting 작업 http://www.lart.tudelft.nl/lartware/blob http://www.linuxdeveloper.co.kr - 임베디드 리눅스 강좌