uboot下ARMV8 lowlevel_init

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最新推荐文章于 2024-12-03 16:44:54 发布

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分类专栏： uboot 源码研究

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本文介绍了lowlevel_init函数的实现细节，该函数用于设置临时栈，调用非常早期的初始化函数s_init，完成基本的启动任务。它不涉及DRAM设置、使用全局数据、清除BSS或尝试启动控制台。

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lowlevel_init:

#include <asm-offsets.h>
#include <config.h>
#include <linux/linkage.h>
ENTRY(lowlevel_init)
 /*
  * Setup a temporary stack. Global data is not available yet.
  */
#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
 ldr w0, =CONFIG_SPL_STACK
#else
 ldr w0, =CONFIG_SYS_INIT_SP_ADDR
#endif
 bic sp, x0, #0xf /* 16-byte alignment for ABI compliance */
 /*
  * Save the old LR(passed in x29) and the current LR to stack
  */
 stp x29, x30, [sp, #-16]!
 /*
  * Call the very early init function. This should do only the
  * absolute bare minimum to get started. It should not:
  *
  * - set up DRAM
  * - use global_data
  * - clear BSS
  * - try to start a console
  *
  * For boards with SPL this should be empty since SPL can do all of
  * this init in the SPL board_init_f() function which is called
  * immediately after this.
  */
 bl s_init
 ldp x29, x30, [sp]
 ret
ENDPROC(lowlevel_init)