README.standalone (ced6466ed520749ea73651b45fabeb5a3efa9c8b) README.standalone (0df01fd3d71481b5cc7aeea6a741b9fc3be15178)
1Design Notes on Exporting U-Boot Functions to Standalone Applications:
2======================================================================
3
41. The functions are exported by U-Boot via a jump table. The jump
5 table is allocated and initialized in the jumptable_init() routine
6 (common/exports.c). Other routines may also modify the jump table,
7 however. The jump table can be accessed as the 'jt' field of the
8 'global_data' structure. The slot numbers for the jump table are

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14
15 gd->jt[XF_malloc] = my_malloc;
16 gd->jt[XF_free] = my_free;
17
18 Note that the pointers to the functions all have 'void *' type and
19 thus the compiler cannot perform type checks on these assignments.
20
212. The pointer to the jump table is passed to the application in a
1Design Notes on Exporting U-Boot Functions to Standalone Applications:
2======================================================================
3
41. The functions are exported by U-Boot via a jump table. The jump
5 table is allocated and initialized in the jumptable_init() routine
6 (common/exports.c). Other routines may also modify the jump table,
7 however. The jump table can be accessed as the 'jt' field of the
8 'global_data' structure. The slot numbers for the jump table are

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14
15 gd->jt[XF_malloc] = my_malloc;
16 gd->jt[XF_free] = my_free;
17
18 Note that the pointers to the functions all have 'void *' type and
19 thus the compiler cannot perform type checks on these assignments.
20
212. The pointer to the jump table is passed to the application in a
22 machine-dependent way. PowerPC, ARM, MIPS and Blackfin architectures
23 use a dedicated register to hold the pointer to the 'global_data'
24 structure: r2 on PowerPC, r8 on ARM, k0 on MIPS, and P3 on Blackfin.
25 The x86 architecture does not use such a register; instead, the
26 pointer to the 'global_data' structure is passed as 'argv[-1]'
27 pointer.
22 machine-dependent way. PowerPC, ARM, MIPS, Blackfin and Nios II
23 architectures use a dedicated register to hold the pointer to the
24 'global_data' structure: r2 on PowerPC, r8 on ARM, k0 on MIPS,
25 P3 on Blackfin and gp on Nios II. The x86 architecture does not
26 use such a register; instead, the pointer to the 'global_data'
27 structure is passed as 'argv[-1]' pointer.
28
29 The application can access the 'global_data' structure in the same
30 way as U-Boot does:
31
32 DECLARE_GLOBAL_DATA_PTR;
33
34 printf("U-Boot relocation offset: %x\n", gd->reloc_off);
35

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51 follows:
52
53 Load address Start address
54 x86 0x00040000 0x00040000
55 PowerPC 0x00040000 0x00040004
56 ARM 0x0c100000 0x0c100000
57 MIPS 0x80200000 0x80200000
58 Blackfin 0x00001000 0x00001000
28
29 The application can access the 'global_data' structure in the same
30 way as U-Boot does:
31
32 DECLARE_GLOBAL_DATA_PTR;
33
34 printf("U-Boot relocation offset: %x\n", gd->reloc_off);
35

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51 follows:
52
53 Load address Start address
54 x86 0x00040000 0x00040000
55 PowerPC 0x00040000 0x00040004
56 ARM 0x0c100000 0x0c100000
57 MIPS 0x80200000 0x80200000
58 Blackfin 0x00001000 0x00001000
59 Nios II 0x02000000 0x02000000
59
60 For example, the "hello world" application may be loaded and
61 executed on a PowerPC board with the following commands:
62
63 => tftp 0x40000 hello_world.bin
64 => go 0x40004
65
665. To export some additional function foobar(), the following steps

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61 For example, the "hello world" application may be loaded and
62 executed on a PowerPC board with the following commands:
63
64 => tftp 0x40000 hello_world.bin
65 => go 0x40004
66
675. To export some additional function foobar(), the following steps

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