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Diffstat (limited to 'doc/README.standalone')
| -rw-r--r-- | doc/README.standalone | 41 |
1 files changed, 30 insertions, 11 deletions
diff --git a/doc/README.standalone b/doc/README.standalone index e3000ef..659a12f 100644 --- a/doc/README.standalone +++ b/doc/README.standalone @@ -5,18 +5,18 @@ Design Notes on Exporting U-Boot Functions to Standalone Applications: table is allocated and initialized in the jumptable_init() routine (common/exports.c). Other routines may also modify the jump table, however. The jump table can be accessed as the 'jt' field of the - 'global_data' structure. The slot numbers for the jump table are + 'global_data' structure. The struct members for the jump table are defined in the <include/exports.h> header. E.g., to substitute the malloc() and free() functions that will be available to standalone applications, one should do the following: DECLARE_GLOBAL_DATA_PTR; - gd->jt[XF_malloc] = my_malloc; - gd->jt[XF_free] = my_free; + gd->jt->malloc = my_malloc; + gd->jt->free = my_free; - Note that the pointers to the functions all have 'void *' type and - thus the compiler cannot perform type checks on these assignments. + Note that the pointers to the functions are real function pointers + so the compiler can perform type checks on these assignments. 2. The pointer to the jump table is passed to the application in a machine-dependent way. PowerPC, ARM, MIPS, Blackfin and Nios II @@ -65,27 +65,46 @@ Design Notes on Exporting U-Boot Functions to Standalone Applications: => tftp 0x40000 hello_world.bin => go 0x40004 -5. To export some additional function foobar(), the following steps +5. To export some additional function long foobar(int i,char c), the following steps should be undertaken: - Append the following line at the end of the include/_exports.h file: - EXPORT_FUNC(foobar) + EXPORT_FUNC(foobar, long, foobar, int, char) + + Parameters to EXPORT_FUNC: + - the first parameter is the function that is exported (default implementation) + - the second parameter is the return value type + - the third parameter is the name of the member in struct jt_funcs + this is also the name that the standalone application will used. + the rest of the parameters are the function arguments - Add the prototype for this function to the include/exports.h file: - void foobar(void); + long foobar(int i, char c); + + Initialization with the default implementation is done in jumptable_init() + + You can override the default implementation using: - - Add the initialization of the jump table slot wherever - appropriate (most likely, to the jumptable_init() function): + gd->jt->foobar = another_foobar; - gd->jt[XF_foobar] = foobar; + The signature of another_foobar must then match the declaration of foobar. - Increase the XF_VERSION value by one in the include/exports.h file + - If you want to export a function which depends on a CONFIG_XXX + use 2 lines like this: + #ifdef CONFIG_FOOBAR + EXPORT_FUNC(foobar, long, foobar, int, char) + #else + EXPORT_FUNC(dummy, void, foobar, void) + #endif + + 6. The code for exporting the U-Boot functions to applications is mostly machine-independent. The only places written in assembly language are stub functions that perform the jump through the jump |