nuttx-OS启动前的准备工作
司寇烨伟
程序的基本编译过程为：预处理、编译成汇编语言、汇编成机器指令、链接成可执行文件，链接依赖于链接脚本，使用链接脚本来进行更复杂的地址设置，包括了代码段，数据段，bss段等，nuttx就使用ARCHSCRIPT宏来指定链接文件，下面以nucleo-l432kc为例，进行跟踪。
nuttx/boards/arm/stm32l4/nucleo-l432kc/scripts/l432kc.ld
MEMORY
{
flash (rx) : ORIGIN = 0x08000000, LENGTH = 256K
sram (rwx) : ORIGIN = 0x20000000, LENGTH = 64K
}
OUTPUT_ARCH(arm)
ENTRY(_stext)
SECTIONS
{
.text : {
_stext = ABSOLUTE(.);
*(.vectors)
*(.text .text.*)
*(.fixup)
*(.gnu.warning)
*(.rodata .rodata.*)
*(.gnu.linkonce.t.*)
*(.glue_7)
*(.glue_7t)
*(.got)
*(.gcc_except_table)
*(.gnu.linkonce.r.*)
_etext = ABSOLUTE(.);
} > flash
.init_section : {
_sinit = ABSOLUTE(.);
*(.init_array .init_array.*)
_einit = ABSOLUTE(.);
} > flash
.ARM.extab : {
*(.ARM.extab*)
} > flash
__exidx_start = ABSOLUTE(.);
.ARM.exidx : {
*(.ARM.exidx*)
} > flash
__exidx_end = ABSOLUTE(.);
_eronly = ABSOLUTE(.);
/* The STM32L432KC has 64Kb of SRAM beginning at the following address */
.data : {
_sdata = ABSOLUTE(.);
*(.data .data.*)
*(.gnu.linkonce.d.*)
CONSTRUCTORS
. = ALIGN(4);
_edata = ABSOLUTE(.);
} > sram AT > flash
.bss : {
_sbss = ABSOLUTE(.);
*(.bss .bss.*)
*(.gnu.linkonce.b.*)
*(COMMON)
. = ALIGN(4);
_ebss = ABSOLUTE(.);
} > sram
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
.debug_abbrev 0 : { *(.debug_abbrev) }
.debug_info 0 : { *(.debug_info) }
.debug_line 0 : { *(.debug_line) }
.debug_pubnames 0 : { *(.debug_pubnames) }
.debug_aranges 0 : { *(.debug_aranges) }
}
stm32l4是基于Armv7E-M架构，nuttx/arch/arm/src/armv7-m/arm_vectors.c
#include "chip.h"
#include "arm_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define IDLE_STACK ((unsigned)&_ebss+CONFIG_IDLETHREAD_STACKSIZE)
#ifndef ARMV7M_PERIPHERAL_INTERRUPTS
# error ARMV7M_PERIPHERAL_INTERRUPTS must be defined to the number of I/O interrupts to be supported
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
/* Chip-specific entrypoint */
extern void __start(void);
/* Common exception entrypoint */
extern void exception_common(void);
/****************************************************************************
* Public data
****************************************************************************/
/* The v7m vector table consists of an array of function pointers, with the
* first slot (vector zero) used to hold the initial stack pointer.
*
* As all exceptions (interrupts) are routed via exception_common, we just
* need to fill this array with pointers to it.
*
* Note that the [ ... ] designated initializer is a GCC extension.
*/
unsigned _vectors[] locate_data(".vectors") =
{
/* Initial stack */
IDLE_STACK,
/* Reset exception handler */
(unsigned)&__start,
/* Vectors 2 - n point directly at the generic handler */
[2 ... (15 + ARMV7M_PERIPHERAL_INTERRUPTS)] = (unsigned)&exception_common
};
make menuconfig中配置CONFIG_IDLETHREAD_STACKSIZE，默认为4096
IDLE_STACK对应占用flash前四个字节，摆放栈起始地址。
复位入口函数__start
中断向量表
复位入口函数定义在：arch/arm/src/stm32l4/stm32l4_start.c 中
void __start(void)
{
const uint32_t *src;
uint32_t *dest;
#ifdef CONFIG_ARMV7M_STACKCHECK
/* Set the stack limit before we attempt to call any functions */
__asm__ volatile("sub r10, sp, %0" : :
"r"(CONFIG_IDLETHREAD_STACKSIZE - 64) :);
#endif
#ifdef CONFIG_STM32L4_SRAM2_INIT
/* The SRAM2 region is parity checked, but upon power up, it will be in
* a random state and probably invalid with respect to parity, potentially
* generating faults if accessed. If elected, we will write zeros to the
* memory, forcing the parity to be set to a valid state.
* NOTE: this is optional because this may be inappropriate, especially
* if the memory is being used for it's battery backed purpose. In that
* case, the first-time initialization needs to be performed by the board
* under application-specific circumstances. On the other hand, if we're
* using this memory for, say, additional heap space, then this is handy.
*/
for (dest = (uint32_t *)SRAM2_START; dest < (uint32_t *)SRAM2_END; )
{
*dest++ = 0;
}
#endif
/* Configure the UART so that we can get debug output as soon as possible */
stm32l4_clockconfig();
stm32l4_fpuconfig();
stm32l4_lowsetup();
stm32l4_gpioinit();
showprogress('A');
/* Clear .bss. We'll do this inline (vs. calling memset) just to be
* certain that there are no issues with the state of global variables.
*/
for (dest = &_sbss; dest < &_ebss; )
{
*dest++ = 0;
}
showprogress('B');
/* Move the initialized data section from his temporary holding spot in
* FLASH into the correct place in SRAM. The correct place in SRAM is
* give by _sdata and _edata. The temporary location is in FLASH at the
* end of all of the other read-only data (.text, .rodata) at _eronly.
*/
for (src = &_eronly, dest = &_sdata; dest < &_edata; )
{
*dest++ = *src++;
}
showprogress('C');
/* Perform early serial initialization */
#ifdef USE_EARLYSERIALINIT
arm_earlyserialinit();
#endif
showprogress('D');
/* For the case of the separate user-/kernel-space build, perform whatever
* platform specific initialization of the user memory is required.
* Normally this just means initializing the user space .data and .bss
* segments.
*/
#ifdef CONFIG_BUILD_PROTECTED
stm32l4_userspace();
showprogress('E');
#endif
/* Initialize onboard resources */
stm32l4_board_initialize();
showprogress('F');
/* Then start NuttX */
showprogress('\r');
showprogress('\n');
nx_start();
/* Shouldn't get here */
for (; ; );
}
__start函数包含了板级初始化等相关内容，都是操作系统启动前的准备工作，最后通过nx_start函数，启动nuttx操作系统。
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