, single-chip microcomputer has a minimum system, the so-called minimum system is single chip microcomputer can work normally required for peripherals, at least for Uboot, also have a minimum system, because the main function is to guide the kernel Uboot, below we analysis through a simple Mini - Uboot Uboot start the loading process, (just the analysis process, the Uboot has guided the kernel function)
Note: just the uboot has the basic function of the kernel boot, just as the early learning to use a simple, starter, and not normal uboot startup process
Here is the root of the mini - uboot tree:
We get a project, want to understand its function, the most convenient is the makefile to read it,
A, the Makefile
(CPP) view plain copy
1. Sinclude include/config. Mk
2.
3. # ARCH=arm
4. # CPU=arm920t
5. # VENDOR=samsung
6. #=s3c2410 SOC
7. # BOARD=smdk2410
8.
9. SRC_TREE:=$(shell PWD)
10. MKCONFIG=$(SRC_TREE)/MKCONFIG
11.
12. INCLUDE_PATH=include
13. DRIVER_PATH=driver
14. LIB_DIR=lib
15.
16.
17. CFLAG=- mabi=apcs - gnu - fno - builtin - fno - builtin function - g - O0 - c - I $(INCLUDE_PATH) - I $(DRIVER_PATH) - o
18. LDFLAG=- Tcpu/arm/arm_cortexa8/map. Typical vmlinux.lds -o
19. The OBJS=CPU/$(ARCH)/$(CPU)/start. O
20. OBJS +=lib_arm/board. O
21. The OBJS +=board/$(VENDOR)/$(board)/lowlevel_init. O
22. The OBJS +=board/$(VENDOR)/$(board)/mem_setup. O
23. The OBJS +=board/$(VENDOR)/$(board)/nand. O
24. The OBJS +=driver/uart. O
25. The OBJS +=lib/string. O
26. The OBJS +=common/do_go. O
27. The OBJS +=common/main. O
28.
29. Ifeq ($(ARCH), arm)
30. CROSS_COMPILE=arm - cortex_a8 - Linux - gnueabi -
31. The endif
32.
33. PROJ_NAME=mini_uboot
34.
35. All: $(OBJS)
36. $(CROSS_COMPILE) ld $(OBJS) $(LDFLAG) $(PROJ_NAME). The elf
37. The binary $$(CROSS_COMPILE) objcopy - O (PROJ_NAME). The elf $(PROJ_NAME). Bin
38. $(CROSS_COMPILE) objdump -d $(PROJ_NAME). The elf & gt; $(PROJ_NAME). Dis
39. The cp *. Bin/tftpboot
40.
41. %. O: % S
42. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
43. %. O: % s
44. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
45.
46. %. O: c
%.
47. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
48.
49. Fsc100_config: # ARCH CPU VENDOR BOARD SOC
50. At $(MKCONFIG) $(@ : _config=) arm arm_cortexa8 samsung fsc100 s5pc100
51. # mkconfig fsc100 arm arm_cortexa8 samsung fsc100 s5pc100
52.
53. Smdk2410_config: # ARCH CPU VENDOR BOARD SOC
54. $(MKCONFIG) $(@ : _config=) arm arm920t samsung smdk2410 s3c2410
55.
56. The clean:
57. @ the rm - rf $(OBJS) *. Bin *. The elf config. Mk
Here in 2440, for example, let's analysis:
(CPP) view plain copy
1. # ARCH=arm
2. # CPU=arm920t
3. # VENDOR=samsung
4. #=s3c2410 SOC
5. # BOARD=smdk2410
Architecture of arm CPU for arm920t, manufacturers samsung, on-chip system sc2410, board for smdk2410,
(CPP) view plain copy
1. The OBJS=CPU/$(ARCH)/$(CPU)/start. O
2. OBJS +=lib_arm/board. O
3. The OBJS +=board/$(VENDOR)/$(board)/lowlevel_init. O
4. The OBJS +=board/$(VENDOR)/$(board)/mem_setup. O
5. OBJS +=board/$(VENDOR)/$(board)/nand. O
6. OBJS +=driver/uart. O
7. OBJS +=lib/string. O
8. OBJS +=common/do_go. O
9. The OBJS +=common/main. O
OBJS for relying on file, generated. O file,
(CPP) view plain copy
1. The ifeq ($(ARCH), arm)
2. The CROSS_COMPILE=arm - cortex_a8 - Linux - gnueabi -
3. The endif
According to the corresponding architecture, making the corresponding cross compile tools,
(CPP) view plain copy
1. All: $(OBJS)
2. $(CROSS_COMPILE) ld $(OBJS) $(LDFLAG) $(PROJ_NAME). The elf
3. The binary $$(CROSS_COMPILE objcopy) - O (PROJ_NAME). The elf $(PROJ_NAME). Bin
4. $(CROSS_COMPILE) objdump -d $(PROJ_NAME). The elf & gt; $(PROJ_NAME). Dis
The first step: to connect; The second step: format conversion; Step 3: the disassembly & gt; "" The meaning of value orientation;
(CPP) view plain copy
1. %. O: % S
2. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
3. %. O: % s
4. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
5.
6. %. O: c
%.
7. $(CROSS_COMPILE) GCC $(CFLAG) $@ $& lt;
All. S files,, S file, compiled into the c file. O file,
Note: S files can be accepted in the compilation process parameters, the S file can not be,
Second, link files
(CPP) view plain copy
1. OUTPUT_FORMAT (" elf32 - littlearm ", "elf32 - littlearm", "elf32 - littlearm")
2./* OUTPUT_FORMAT (" elf32 - arm ", "elf32 - arm", "elf32 - arm") */
3. OUTPUT_ARCH (arm)
4. ENTRY (_start)//specified ENTRY address
5. SECTIONS//segment information
6. {
nullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnull
