移植後的代碼戳這裏: https://code.csdn.net/KISSMonX/freertos_f3discovery_test
在上一篇文章 ARM 彙編中的 "B ." 語句意義.時, 順帶介紹了 [WEAK] 的作用.
昨天再思考移植問題的時候(也就是執行第一個任務時直接跳到 SVC_Handler 裏的 B . 處),
想到了這個問題, 然後在移植配置文件中添加了幾個宏定義就解決了問題, 移植成功, 具體下文介紹.
這裏再做一次解釋. 看看自己是不是真正的理解了. :)
第一步明顯是要貼代碼裝逼, 去啓動文件裏摘取出要介紹的部分. 然後記筆記的形式摘錄下來.如下:
; Reset handler 這裏纔是啓動文件的重點啊. 不過沒見到爲 C 程序建立棧空間操作啊??? 直接調用 main 大丈夫? MAN???
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT SystemInit
IMPORT __main
LDR R0, =SystemInit
BLX R0
LDR R0, =__main
BX R0
ENDP
; Dummy Exception Handlers (infinite loops which can be modified)
NMI_Handler PROC
EXPORT NMI_Handler [WEAK]
B .
ENDP
HardFault_Handler\
PROC
EXPORT HardFault_Handler [WEAK]
B .
ENDP
MemManage_Handler\
PROC
EXPORT MemManage_Handler [WEAK]
B .
ENDP
BusFault_Handler\
PROC
EXPORT BusFault_Handler [WEAK]
B .
ENDP
UsageFault_Handler\
PROC
EXPORT UsageFault_Handler [WEAK]
B .
ENDP
SVC_Handler PROC
EXPORT SVC_Handler [WEAK]
B .
ENDP
DebugMon_Handler\
PROC
EXPORT DebugMon_Handler [WEAK]
B .
ENDP
PendSV_Handler PROC
EXPORT PendSV_Handler [WEAK]
B .
ENDP
SysTick_Handler PROC
EXPORT SysTick_Handler [WEAK]
B .
ENDP
Default_Handler PROC
EXPORT WWDG_IRQHandler [WEAK]
EXPORT PVD_IRQHandler [WEAK]
EXPORT TAMPER_STAMP_IRQHandler [WEAK]
EXPORT RTC_WKUP_IRQHandler [WEAK]
EXPORT FLASH_IRQHandler [WEAK]
EXPORT RCC_IRQHandler [WEAK]
EXPORT EXTI0_IRQHandler [WEAK]
EXPORT EXTI1_IRQHandler [WEAK]
EXPORT EXTI2_TS_IRQHandler [WEAK]
EXPORT EXTI3_IRQHandler [WEAK]
EXPORT EXTI4_IRQHandler [WEAK]
EXPORT DMA1_Channel1_IRQHandler [WEAK]
EXPORT DMA1_Channel2_IRQHandler [WEAK]
EXPORT DMA1_Channel3_IRQHandler [WEAK]
EXPORT DMA1_Channel4_IRQHandler [WEAK]
EXPORT DMA1_Channel5_IRQHandler [WEAK]
EXPORT DMA1_Channel6_IRQHandler [WEAK]
EXPORT DMA1_Channel7_IRQHandler [WEAK]
EXPORT ADC1_2_IRQHandler [WEAK]
EXPORT USB_HP_CAN1_TX_IRQHandler [WEAK]
EXPORT USB_LP_CAN1_RX0_IRQHandler [WEAK]
EXPORT CAN1_RX1_IRQHandler [WEAK]
EXPORT CAN1_SCE_IRQHandler [WEAK]
EXPORT EXTI9_5_IRQHandler [WEAK]
EXPORT TIM1_BRK_TIM15_IRQHandler [WEAK]
EXPORT TIM1_UP_TIM16_IRQHandler [WEAK]
EXPORT TIM1_TRG_COM_TIM17_IRQHandler [WEAK]
EXPORT TIM1_CC_IRQHandler [WEAK]
EXPORT TIM2_IRQHandler [WEAK]
EXPORT TIM3_IRQHandler [WEAK]
EXPORT TIM4_IRQHandler [WEAK]
EXPORT I2C1_EV_IRQHandler [WEAK]
EXPORT I2C1_ER_IRQHandler [WEAK]
EXPORT I2C2_EV_IRQHandler [WEAK]
EXPORT I2C2_ER_IRQHandler [WEAK]
EXPORT SPI1_IRQHandler [WEAK]
EXPORT SPI2_IRQHandler [WEAK]
EXPORT USART1_IRQHandler [WEAK]
EXPORT USART2_IRQHandler [WEAK]
EXPORT USART3_IRQHandler [WEAK]
EXPORT EXTI15_10_IRQHandler [WEAK]
EXPORT RTC_Alarm_IRQHandler [WEAK]
EXPORT USBWakeUp_IRQHandler [WEAK]
EXPORT TIM8_BRK_IRQHandler [WEAK]
EXPORT TIM8_UP_IRQHandler [WEAK]
EXPORT TIM8_TRG_COM_IRQHandler [WEAK]
EXPORT TIM8_CC_IRQHandler [WEAK]
EXPORT ADC3_IRQHandler [WEAK]
EXPORT SPI3_IRQHandler [WEAK]
EXPORT UART4_IRQHandler [WEAK]
EXPORT UART5_IRQHandler [WEAK]
EXPORT TIM6_DAC_IRQHandler [WEAK]
EXPORT TIM7_IRQHandler [WEAK]
EXPORT DMA2_Channel1_IRQHandler [WEAK]
EXPORT DMA2_Channel2_IRQHandler [WEAK]
EXPORT DMA2_Channel3_IRQHandler [WEAK]
EXPORT DMA2_Channel4_IRQHandler [WEAK]
EXPORT DMA2_Channel5_IRQHandler [WEAK]
EXPORT ADC4_IRQHandler [WEAK]
EXPORT COMP1_2_3_IRQHandler [WEAK]
EXPORT COMP4_5_6_IRQHandler [WEAK]
EXPORT COMP7_IRQHandler [WEAK]
EXPORT USB_HP_IRQHandler [WEAK]
EXPORT USB_LP_IRQHandler [WEAK]
EXPORT USBWakeUp_RMP_IRQHandler [WEAK]
EXPORT FPU_IRQHandler [WEAK] 然後到 keil 的幫助文檔裏找到這麼一句話:
/* WEAK : symbol is only imported into other sources if no other source exports an alternative symbol.
If [WEAK] is used without symbol, all exported symbols are weak. */緊接着下面就有這種介紹:
比我介紹的詳細準確多了.
英語不好的就算了吧. 大致意思就是:
// 意思就是告訴鏈接器:
// "我略弱但我很紳士, 如果你在別處看到和我一樣的符號實例.你就用它吧. 表管我, 求忽視! " 所以......知道這個, 就可以解決爲什麼 FreeRTOS 在執行到下面這段代碼老是跳轉到 SVC_Handler 處了.
<亂入> SVC 作用: SVCall A supervisor call (SVC) is
an exception that is triggered by the SVC instruction. In an OS environment, applications can use SVC instructions to
access OS kernel functions and device drivers.
__asm void prvStartFirstTask( void )
{
PRESERVE8
/* Use the NVIC offset register to locate the stack. */
ldr r0, =0xE000ED08
ldr r0, [r0]
ldr r0, [r0]
/* Set the msp back to the start of the stack. */
msr msp, r0
/* Globally enable interrupts. */
cpsie i
dsb
isb
/* Call SVC to start the first task. */
svc 0 // 0 號系統調用, 更多關於 SVC 可以參考 google 或者 ARM Cortex-M3 權威指南
nop
}而且特意加上了 [WEAK] 修飾. 這樣用戶可以根據自己的需要重新編寫自己的處理函數, 而且只要命名一樣就 OK 了.
那名字要是不一樣怎麼辦? 然後, 我去找了 SVC_Handler 這個名字, 並沒有找到, 但是在 port.c 中找到了
下面這個函數:
__asm void vPortSVCHandler( void )
{
PRESERVE8
/* Get the location of the current TCB. */
ldr r3, =pxCurrentTCB
ldr r1, [r3]
ldr r0, [r1]
/* Pop the core registers. */
ldmia r0!, {r4-r11, r14}
msr psp, r0
isb
mov r0, #0
msr basepri, r0
bx r14
}然後我當然沒有那麼聰明, 我找到了以前移植過的文件看了一下, 發現在 portmacro.h 中有下面三個宏定義:
#define vPortSVCHandler SVC_Handler
#define xPortSysTickHandler SysTick_Handler
#define xPortPendSVHandler PendSV_Handler
