1Generic TPL framework 2===================== 3 4Overview 5-------- 6 7TPL---Third Program Loader. 8 9Due to the SPL on some boards(powerpc mpc85xx) has a size limit and cannot 10be compatible with all the external device(e.g. DDR). So add a tertiary 11program loader (TPL) to enable a loader stub loaded by the code from the 12SPL. It loads the final uboot image into DDR, then jump to it to begin 13execution. Now, only the powerpc mpc85xx has this requirement and will 14implemente it. 15 16Keep consistent with SPL, with this framework almost all source files for a 17board can be reused. No code duplication or symlinking is necessary anymore. 18 19How it works 20------------ 21 22There has been a directory $(srctree)/spl which contains only a Makefile. The 23Makefile is shared by SPL and TPL. 24 25The object files are built separately for SPL/TPL and placed in the 26directory spl/tpl. The final binaries which are generated are 27u-boot-{spl|tpl}, u-boot-{spl|tpl}.bin and u-boot-{spl|tpl}.map. 28 29During the TPL build a variable named CONFIG_TPL_BUILD is exported in the 30make environment and also appended to CPPFLAGS with -DCONFIG_TPL_BUILD. 31 32The SPL options are shared by SPL and TPL, the board config file should 33determine which SPL options to choose based on whether CONFIG_TPL_BUILD 34is set. Source files can be compiled for TPL with options choosed in the 35board config file. 36 37For example: 38 39spl/Makefile: 40LIBS-$(CONFIG_SPL_LIBCOMMON_SUPPORT) += common/libcommon.o 41 42CONFIG_SPL_LIBCOMMON_SUPPORT is defined in board config file: 43#ifdef CONFIG_TPL_BUILD 44#define CONFIG_SPL_LIBCOMMON_SUPPORT 45#endif 46