2 * crt0 - C-runtime startup Code for ARM U-Boot
4 * Copyright (c) 2012 Albert ARIBAUD <albert.u.boot@aribaud.net>
6 * SPDX-License-Identifier: GPL-2.0+
10 #include <asm-offsets.h>
11 #include <linux/linkage.h>
14 * This file handles the target-independent stages of the U-Boot
15 * start-up where a C runtime environment is needed. Its entry point
16 * is _main and is branched into from the target's start.S file.
18 * _main execution sequence is:
20 * 1. Set up initial environment for calling board_init_f().
21 * This environment only provides a stack and a place to store
22 * the GD ('global data') structure, both located in some readily
23 * available RAM (SRAM, locked cache...). In this context, VARIABLE
24 * global data, initialized or not (BSS), are UNAVAILABLE; only
25 * CONSTANT initialized data are available.
27 * 2. Call board_init_f(). This function prepares the hardware for
28 * execution from system RAM (DRAM, DDR...) As system RAM may not
29 * be available yet, , board_init_f() must use the current GD to
30 * store any data which must be passed on to later stages. These
31 * data include the relocation destination, the future stack, and
32 * the future GD location.
34 * (the following applies only to non-SPL builds)
36 * 3. Set up intermediate environment where the stack and GD are the
37 * ones allocated by board_init_f() in system RAM, but BSS and
38 * initialized non-const data are still not available.
40 * 4. Call relocate_code(). This function relocates U-Boot from its
41 * current location into the relocation destination computed by
44 * 5. Set up final environment for calling board_init_r(). This
45 * environment has BSS (initialized to 0), initialized non-const
46 * data (initialized to their intended value), and stack in system
47 * RAM. GD has retained values set by board_init_f(). Some CPUs
48 * have some work left to do at this point regarding memory, so
49 * call c_runtime_cpu_setup.
51 * 6. Branch to board_init_r().
55 * entry point of crt0 sequence
61 * Set up initial C runtime environment and call board_init_f(0).
64 #if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
65 ldr sp, =(CONFIG_SPL_STACK)
67 ldr sp, =(CONFIG_SYS_INIT_SP_ADDR)
69 bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
70 sub sp, #GD_SIZE /* allocate one GD above SP */
71 bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
72 mov r9, sp /* GD is above SP */
76 #if ! defined(CONFIG_SPL_BUILD)
79 * Set up intermediate environment (new sp and gd) and call
80 * relocate_code(addr_moni). Trick here is that we'll return
81 * 'here' but relocated.
84 ldr sp, [r9, #GD_START_ADDR_SP] /* sp = gd->start_addr_sp */
85 bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
86 ldr r9, [r9, #GD_BD] /* r9 = gd->bd */
87 sub r9, r9, #GD_SIZE /* new GD is below bd */
90 ldr r0, [r9, #GD_RELOC_OFF] /* r0 = gd->reloc_off */
92 ldr r0, [r9, #GD_RELOCADDR] /* r0 = gd->relocaddr */
96 /* Set up final (full) environment */
98 bl c_runtime_cpu_setup /* we still call old routine here */
100 ldr r0, =__bss_start /* this is auto-relocated! */
101 ldr r1, =__bss_end /* this is auto-relocated! */
103 mov r2, #0x00000000 /* prepare zero to clear BSS */
105 clbss_l:cmp r0, r1 /* while not at end of BSS */
106 strlo r2, [r0] /* clear 32-bit BSS word */
107 addlo r0, r0, #4 /* move to next */
113 /* call board_init_r(gd_t *id, ulong dest_addr) */
114 mov r0, r9 /* gd_t */
115 ldr r1, [r9, #GD_RELOCADDR] /* dest_addr */
116 /* call board_init_r */
117 ldr pc, =board_init_r /* this is auto-relocated! */
119 /* we should not return here. */