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diff --git a/doc/README.TPL b/doc/README.TPL new file mode 100644 index 0000000..1df03b9 --- /dev/null +++ b/doc/README.TPL @@ -0,0 +1,45 @@ +Generic TPL framework +===================== + +Overview +-------- + +TPL---Third Program Loader. + +Due to the SPL on some boards(powerpc mpc85xx) has a size limit and cannot +be compatible with all the external device(e.g. DDR). So add a tertiary +program loader (TPL) to enable a loader stub loaded by the code from the +SPL. It loads the final uboot image into DDR, then jump to it to begin +execution. Now, only the powerpc mpc85xx has this requirement and will +implemente it. + +Keep consistent with SPL, with this framework almost all source files for a +board can be reused. No code duplication or symlinking is necessary anymore. + +How it works +------------ + +There has been a directory TOPDIR/spl which contains only a Makefile. The +Makefile is shared by SPL and TPL. + +The object files are built separately for SPL/TPL and placed in the +directory spl/tpl. The final binaries which are generated are +u-boot-{spl|tpl}, u-boot-{spl|tpl}.bin and u-boot-{spl|tpl}.map. + +During the TPL build a variable named CONFIG_TPL_BUILD is exported in the +make environment and also appended to CPPFLAGS with -DCONFIG_TPL_BUILD. + +The SPL options are shared by SPL and TPL, the board config file should +determine which SPL options to choose based on whether CONFIG_TPL_BUILD +is set. Source files can be compiled for TPL with options choosed in the +board config file. + +For example: + +spl/Makefile: +LIBS-$(CONFIG_SPL_LIBCOMMON_SUPPORT) += common/libcommon.o + +CONFIG_SPL_LIBCOMMON_SUPPORT is defined in board config file: +#ifdef CONFIG_TPL_BUILD +#define CONFIG_SPL_LIBCOMMON_SUPPORT +#endif |