| 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 $(srctree)/spl which contains only a Makefile. The | |
| Makefile is shared by SPL and TPL. | |
| The object files are built separately for SPL/TPL and placed in the | |
| directory spl/tpl. The final binaries which are generated are | |
| u-boot-{spl|tpl}, u-boot-{spl|tpl}.bin and u-boot-{spl|tpl}.map. | |
| During the TPL build a variable named CONFIG_TPL_BUILD is exported in the | |
| make environment and also appended to CPPFLAGS with -DCONFIG_TPL_BUILD. | |
| The SPL options are shared by SPL and TPL, the board config file should | |
| determine which SPL options to choose based on whether CONFIG_TPL_BUILD | |
| is set. Source files can be compiled for TPL with options choosed in the | |
| board config file. | |
| For example: | |
| spl/Makefile: | |
| LIBS-$(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 |