| 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 |
