Source code analysis of uboot
1. ARM SOC startup process
- BL0: the first stage startup code, solidified in the SOC on-chip ROM, cannot be modified;
- BL1: power on and start the second stage, which is loaded into SRAM in BL0 stage, corresponding to SPL stage of u-boot;
- BL2: the third stage of power on and startup, which is loaded into SDRAM in BL1 stage, corresponding to the U boot stage of u-boot.
Created with Rapha ë l 2.2.0 power on to start BL0(IROM)BL0(IROM): Initialize (system clock, SRAM, etc.) BL0(IROM): verify BL1 image BL0(IROM): load BL1 image to SRAMBL0(IROM): jump to bl1BL1(IRAM): u-boot-splbl1 (IRAM): initialize SDRAM, stack BL1(IRAM): verify, load BL2 image to SDRAMBL1(IRAM): jump to BL2BL2(SDRAM): u-boot-bootloader BL2 (SDRAM): load Kernel file system start running application
2. Overview of main loop() call process
/* u-boot-2019.04 */ u-boot-spl.lds(/arch/arm/cpu) ..............|→_start(/arch/arm/lib/vectors.S) ......................|→reset(/arch/arm/cpu/arm920t/start.S) .............................|→cpu_init_crit(/arch/arm/cpu/arm920t/start.S) ............................................|→lowlevel_init(/arch/arm/cpu/mach-xx/lowlevel_init.S) .............................|→_main(/arch/arm/lib/crt0.S) ....................................|→board_init_f_alloc_reserve(/common/init/board_init.c) ....................................|→board_init_f_init_reserve(/common/init/board_init.c) ....................................|→board_init_f ....................................|→board_init_r .................................................|→initcall_run_list ...................................................................|→run_main_loop .................................................................................|→main_loop
/* u-boot-2010.03 */ u-boot.lds .........|→_start(/cpu/arm920t/start.S) ................|→start_code(/cpu/arm920t/start.S) ...........................|→cpu_init_crit(/cpu/arm920t/start.S) .........................................|→lowlevel_init(lowlevel_init.S) ...........................|→_start_armboot(/cpu/arm920t/start.S) ..........................................|→start_armboot(/lib_arm/board.c) ........................................................|→main_loop(/common/main.c)
3. Analysis of two ways of uboot parsing user commands
/* u-boot-2010.03 code snippet */
#Ifdef config sys hush parser / / user command resolution mode 1: hush mode
parse_file_outer();
/* This point is never reached */
for (;;);
#else / / user command resolution mode 2
for (;;) {
...
...
...
len = readline (CONFIG_SYS_PROMPT);
flag = 0; /* assume no special flags for now */
if (len > 0)
strcpy (lastcommand, console_buffer);
else if (len == 0)
flag |= CMD_FLAG_REPEAT;
...
...
...
if (len == -1)
puts ("<INTERRUPT>\n");
else
rc = run_command (lastcommand, flag);
if (rc <= 0) {
/* invalid command or not repeatable, forget it */
lastcommand[0] = 0;
}
}
#endif /*CONFIG_SYS_HUSH_PARSER*/
3.1 mode 1
parse_file_outer ...............|→parse_stream_outer ..................................|→run_list ............................................|→run_list_real ..........................................................|→run_pipe_real ........................................................................|→cmdtp->cmd
3.2 mode 2
readline .......|→readline_into_buffer //read data to consol_buffer run_command ..........|→parse_line //parse command line ..........|→find_cmd //find out command from command table ..........|→cmdtp->cmd