关于rt_hw_context_switch_to的问题

发布于 2017-07-22 23:36:43 浏览：3182 订阅该版

现在在学习rtthread-2.1.0的`rt_hw_context_switch_to(rt_uint32 to)`代码。
请问下这里是否有错误？用红字标出来了

```c
NVIC_SYSPRI2    EQU     0xE000ED20    ; system priority register (2)
                                                     ; 调试监视器的优先级 
NVIC_PENDSV_PRI EQU     0x00FF0000  ; PendSV priority value (lowest)
rt_hw_context_switch_to:
    LDR     r1, =rt_interrupt_to_thread   
    STR     r0, [r1]

; set from thread to 0
    LDR     r1, =rt_interrupt_from_thread  
    MOV     r0, #0x0					  
    STR     r0, [r1]

; set interrupt flag to 1
    LDR     r1, =rt_thread_switch_interrupt_flag
    MOV     r0, #1
    STR     r0, [r1]

; set the PendSV exception priority
    LDR     r0, =NVIC_SYSPRI2   ;调试监视器的优先级
                   ;似乎应该是PendSV 的优先级PRI_14? equ 0xE000_ED22?
       ***_LDR     r0, =PRI_14_***

LDR     r1, =NVIC_PENDSV_PRI
    LDR.W   r2, [r0,#0x00]       ; read
    ORR     r1,r1,r2             ; modify
    STR     r1, [r0]             ; write-back

LDR     r0, =NVIC_INT_CTRL      
    LDR     r1, =NVIC_PENDSVSET
    STR     r1, [r0]

; restore MSP
    LDR     r0, =SCB_VTOR        
    LDR     r0, [r0]               
    LDR     r0, [r0]              
    NOP
    MSR     msp, r0

CPSIE   I                       ; enable interrupts at processor level

; never reach here!  
    ;为啥到达不了这里，是因为上一句使能了中断
    ;紧接着程序运行到异常处理PendSV_Handler吗？这样理解对吗？

; compatible with old version
    EXPORT rt_hw_interrupt_thread_switch
rt_hw_interrupt_thread_switch:
    BX      lr
```

8 个回答

aozima 2017-07-23

调网络不抓包，调I2C等时序不上逻辑分析仪，就像电工不用万用表！多用整理的好的文字，比截图更省流量，还能在整理过程中思考。

zwj 2017-07-23

这家伙很懒，什么也没写！

zwj 2017-07-23

这家伙很懒，什么也没写！

现在在学习rtthread-2.1.0的`rt_hw_context_switch_to(rt_uint32 to)`代码。
请问下这里是否有错误？用红字标出来了

```c
NVIC_SYSPRI2    EQU     0xE000ED20      ; system priority register (2)[/color]
    EXPORT rt_hw_context_switch_to
rt_hw_context_switch_to:
    LDR     r1, =rt_interrupt_to_thread
    STR     r0, [r1]

; set from thread to 0
    LDR     r1, =rt_interrupt_from_thread
    MOV     r0, #0x0
    STR     r0, [r1]

; set interrupt flag to 1
    LDR     r1, =rt_thread_switch_interrupt_flag
    MOV     r0, #1
    STR     r0, [r1]

; set the PendSV exception priority
    LDR     r0, =NVIC_SYSPRI2 ;应该是0xE000ED22? PRI_14，而不是0xE000ED20调试监视器的优先级[/color] 
    LDR     r1, =NVIC_PENDSV_PRI
    LDR.W   r2, [r0,#0x00]       ; read
    ORR     r1,r1,r2             ; modify
    STR     r1, [r0]             ; write-back

LDR     r0, =NVIC_INT_CTRL      ; trigger the PendSV exception (causes context switch)
    LDR     r1, =NVIC_PENDSVSET
    STR     r1, [r0]

; restore MSP
    LDR     r0, =SCB_VTOR
    LDR     r0, [r0]
    LDR     r0, [r0]
    NOP
    MSR     msp, r0

CPSIE   I                       ; enable interrupts at processor level

; never reach here!
; compatible with old version
    EXPORT rt_hw_interrupt_thread_switch
rt_hw_interrupt_thread_switch:
    BX      lr
```