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Daniel Schwierzeck6a11cf42011-07-18 07:48:07 +00001Generic SPL framework
2=====================
3
4Overview
5--------
6
7To unify all existing implementations for a secondary program loader (SPL)
8and to allow simply adding of new implementations this generic SPL framework
9has been created. With this framework almost all source files for a board
10can be reused. No code duplication or symlinking is necessary anymore.
11
12
13How it works
14------------
15
16There is a new directory TOPDIR/spl which contains only a Makefile.
17The object files are built separately for SPL and placed in this directory.
18The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
19u-boot-spl.map.
20
21During the SPL build a variable named CONFIG_SPL_BUILD is exported
22in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD.
23Source files can therefore be compiled for SPL with different settings.
24ARM-based boards have previously used the option CONFIG_PRELOADER for it.
25
26For example:
27
28ifeq ($(CONFIG_SPL_BUILD),y)
29COBJS-y += board_spl.o
30else
31COBJS-y += board.o
32endif
33
34COBJS-$(CONFIG_SPL_BUILD) += foo.o
35
36#ifdef CONFIG_SPL_BUILD
37 foo();
38#endif
39
40
41The building of SPL images can be with:
42
43#define CONFIG_SPL
44
45Because SPL images normally have a different text base, one have to be
46configured by defining CONFIG_SPL_TEXT_BASE. The linker script have to be
47defined with CONFIG_SPL_LDSCRIPT.
48
49To support generic U-Boot libraries and drivers in the SPL binary one can
50optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
51are supported:
52
53CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
54CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
55CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
56CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
57CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
58CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
59CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
60CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
61CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)
62CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)