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1 | Generic SPL framework | |
2 | ===================== | |
3 | ||
4 | Overview | |
5 | -------- | |
6 | ||
7 | To unify all existing implementations for a secondary program loader (SPL) | |
8 | and to allow simply adding of new implementations this generic SPL framework | |
9 | has been created. With this framework almost all source files for a board | |
10 | can be reused. No code duplication or symlinking is necessary anymore. | |
11 | ||
12 | ||
13 | How it works | |
14 | ------------ | |
15 | ||
16 | The object files for SPL are built separately and placed in the "spl" directory. | |
17 | The final binaries which are generated are u-boot-spl, u-boot-spl.bin and | |
18 | u-boot-spl.map. | |
19 | ||
20 | A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL. | |
21 | Source files can therefore be compiled for SPL with different settings. | |
22 | ||
23 | For example: | |
24 | ||
25 | ifeq ($(CONFIG_SPL_BUILD),y) | |
26 | obj-y += board_spl.o | |
27 | else | |
28 | obj-y += board.o | |
29 | endif | |
30 | ||
31 | obj-$(CONFIG_SPL_BUILD) += foo.o | |
32 | ||
33 | #ifdef CONFIG_SPL_BUILD | |
34 | foo(); | |
35 | #endif | |
36 | ||
37 | ||
38 | The building of SPL images can be enabled by CONFIG_SPL option in Kconfig. | |
39 | ||
40 | Because SPL images normally have a different text base, one has to be | |
41 | configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be | |
42 | defined with CONFIG_SPL_LDSCRIPT. | |
43 | ||
44 | To support generic U-Boot libraries and drivers in the SPL binary one can | |
45 | optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options | |
46 | are supported: | |
47 | ||
48 | CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) | |
49 | CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) | |
50 | CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o) | |
51 | CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o) | |
52 | CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o) | |
53 | CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o) | |
54 | CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) | |
55 | CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o) | |
56 | CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o) | |
57 | CONFIG_SPL_EXT_SUPPORT | |
58 | CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) | |
59 | CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o) | |
60 | CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o) | |
61 | CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc) | |
62 | CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o) | |
63 | CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o) | |
64 | CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o) | |
65 | CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o) | |
66 | CONFIG_SPL_RAM_DEVICE (common/spl/spl.c) | |
67 | CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o) | |
68 | ||
69 | ||
70 | Debugging | |
71 | --------- | |
72 | ||
73 | When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG | |
74 | as in most cases do_reset is not defined within SPL. | |
75 | ||
76 | ||
77 | Estimating stack usage | |
78 | ---------------------- | |
79 | ||
80 | With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate | |
81 | stack usage at various points in run sequence of SPL. The -fstack-usage option | |
82 | to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that | |
83 | will give stack usage information and cflow can construct program flow. | |
84 | ||
85 | Must have gcc 4.6 or later, which supports -fstack-usage | |
86 | ||
87 | 1) Build normally | |
88 | 2) Perform the following shell command to generate a list of C files used in | |
89 | SPL: | |
90 | $ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list | |
91 | 3) Execute cflow: | |
92 | $ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER | |
93 | ||
94 | cflow will spit out a number of warnings as it does not parse | |
95 | the config files and picks functions based on #ifdef. Parsing the '.i' | |
96 | files instead introduces another set of headaches. These warnings are | |
97 | not usually important to understanding the flow, however. |