Add qemu 2.4.0

[kvmfornfv.git] / qemu / roms / u-boot / doc / README.TPL

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+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