毕业设计之路(9)-ucosi操作系统移植到STM32
这个工作主要是根据网友的经验资料来学习移植的。总的来说需要下面几个参考资料。
ARM Cortex-m3权威指南
官方移植文档资料
网友移植成功经验资料
这三种资料在我的资源上传里面都能找到。
我在官网上下的是官方已经移植好的到STM32F103评估板的资料，很多部分已经实现了，所以需要改动的地方很少，不同的地方可以参考第三种网友移植成功经验资料，里面有详细说明。我下的是ucosii2.86版本。
下面说说移植过程：
移植主要涉及到两个源文件，os_cpu_c.c和os_cpu_a.asm，os_cpu.h。其他文件是ucosii核心文件，不需要修改。还有两个配置文件app_cfg.h和os_cfg.h。
整个文件框架构成图如下，用的是IAR。
这就是对照上面的说明而设置的目录结构。
下面谈主要移植的部分。主要集中在os_cpu_a.asm这个文件中，os_cpu.h主要涉及到一些宏的配置。os_cpu_c.c中主要有一个函数必须写出，就是堆栈初始化函数。
先说os_cpu.h中需要注意的地方。
下面是开关中断的宏
#define OS_CRITICAL_METHOD 3
#if OS_CRITICAL_METHOD == 3
#define OS_ENTER_CRITICAL() {cpu_sr = OS_CPU_SR_Save();}
#define OS_EXIT_CRITICAL() {OS_CPU_SR_Restore(cpu_sr);}
#endif
CM3堆栈方向高到底递减，设置为1，还有一个任务切换的宏。
#define OS_STK_GROWTH 1 /* Stack grows from HIGH to LOW memory on ARM */
#define OS_TASK_SW() OSCtxSw()
还有几个关于systick的函数需要注释掉，下面的os_cpu_c.c会说道原因。
// /* See OS_CPU_C.C */
//void OS_CPU_SysTickHandler(void);
//void OS_CPU_SysTickInit(void);
//
// /* See BSP.C */
//INT32U OS_CPU_SysTickClkFreq(void);
看os_cpu_c.c。
里面有些函数是钩子函数，根据需要写。如果不需要可以不写。
下面是堆栈初始化函数。
/*
*********************************************************************************************************
* INITIALIZE A TASK'S STACK
*
* Description: This function is called by either OSTaskCreate() or OSTaskCreateExt() to initialize the
* stack frame of the task being created. This function is highly processor specific.
*
* Arguments : task is a pointer to the task code
*
* p_arg is a pointer to a user supplied data area that will be passed to the task
* when the task first executes.
*
* ptos is a pointer to the top of stack. It is assumed that 'ptos' points to
* a 'free' entry on the task stack. If OS_STK_GROWTH is set to 1 then
* 'ptos' will contain the HIGHEST valid address of the stack. Similarly, if
* OS_STK_GROWTH is set to 0, the 'ptos' will contains the LOWEST valid address
* of the stack.
*
* opt specifies options that can be used to alter the behavior of OSTaskStkInit().
* (see uCOS_II.H for OS_TASK_OPT_xxx).
*
* Returns : Always returns the location of the new top-of-stack once the processor registers have
* been placed on the stack in the proper order.
*
* Note(s) : 1) Interrupts are enabled when your task starts executing.
* 2) All tasks run in Thread mode, using process stack.
*********************************************************************************************************
*/
OS_STK *OSTaskStkInit (void (*task)(void *p_arg), void *p_arg, OS_STK *ptos, INT16U opt)
{
OS_STK *stk;
(void)opt; /* 'opt' is not used, prevent warning */
stk = ptos; /* Load stack pointer */
/* Registers stacked as if auto-saved on exception */
*(stk) = (INT32U)0x01000000L; /* xPSR */
*(--stk) = (INT32U)task; /* Entry Point */
*(--stk) = (INT32U)0xFFFFFFFEL; /* R14 (LR) (init value will cause fault if ever used)*/
*(--stk) = (INT32U)0x12121212L; /* R12 */
*(--stk) = (INT32U)0x03030303L; /* R3 */
*(--stk) = (INT32U)0x02020202L; /* R2 */
*(--stk) = (INT32U)0x01010101L; /* R1 */
*(--stk) = (INT32U)p_arg; /* R0 : argument */
/* Remaining registers saved on process stack */
*(--stk) = (INT32U)0x11111111L; /* R11 */
*(--stk) = (INT32U)0x10101010L; /* R10 */
*(--stk) = (INT32U)0x09090909L; /* R9 */
*(--stk) = (INT32U)0x08080808L; /* R8 */
*(--stk) = (INT32U)0x07070707L; /* R7 */
*(--stk) = (INT32U)0x06060606L; /* R6 */
*(--stk) = (INT32U)0x05050505L; /* R5 */
*(--stk) = (INT32U)0x04040404L; /* R4 */
return (stk);
}
因为CM3支持的堆栈地址是从高到低递减的，所以里面都是--。而且CM3中断自动入栈顺序为xPSR,PC,R14,R12,R3~R0,这个可以参考CM3权威指南。所以放在前面。后面R11~R4需要我们手动入栈。最后返回栈顶指针。
OS_CPU_C.c中还有一些东西需要我们注释掉，因为官方的资料是根据评估板来写的，如果移植到我们有STM32固件库的平台上，则需要做些改变，这是参考网友移植经验知道的。这些需要注释掉的东西主要是跟systic这个定时器有关。
下面是需要注释掉的地方。
//void OS_CPU_SysTickInit (void)
//{
// INT32U cnts;
//
//
// cnts = OS_CPU_SysTickClkFreq() / OS_TICKS_PER_SEC;
//
// OS_CPU_CM3_NVIC_ST_RELOAD = (cnts - 1);
// /* Enable timer. */
// OS_CPU_CM3_NVIC_ST_CTRL |= OS_CPU_CM3_NVIC_ST_CTRL_CLK_SRC | OS_CPU_CM3_NVIC_ST_CTRL_ENABLE;
// /* Enable timer interrupt. */
// OS_CPU_CM3_NVIC_ST_CTRL |= OS_CPU_CM3_NVIC_ST_CTRL_INTEN;
//}
//void OS_CPU_SysTickHandler (void)
//{
// OS_CPU_SR cpu_sr;
//
//
// OS_ENTER_CRITICAL(); /* Tell uC/OS-II that we are starting an ISR */
// OSIntNesting++;
// OS_EXIT_CRITICAL();
//
// OSTimeTick(); /* Call uC/OS-II's OSTimeTick() */
//
// OSIntExit(); /* Tell uC/OS-II that we are leaving the ISR */
//}
//#define OS_CPU_CM3_NVIC_ST_CTRL (*((volatile INT32U *)0xE000E010)) /* SysTick Ctrl & Status Reg. */
//#define OS_CPU_CM3_NVIC_ST_RELOAD (*((volatile INT32U *)0xE000E014)) /* SysTick Reload Value Reg. */
//#define OS_CPU_CM3_NVIC_ST_CURRENT (*((volatile INT32U *)0xE000E018)) /* SysTick Current Value Reg. */
//#define OS_CPU_CM3_NVIC_ST_CAL (*((volatile INT32U *)0xE000E01C)) /* SysTick Cal Value Reg. */
//
//#define OS_CPU_CM3_NVIC_ST_CTRL_COUNT 0x00010000 /* Count flag. */
//#define OS_CPU_CM3_NVIC_ST_CTRL_CLK_SRC 0x00000004 /* Clock Source. */
//#define OS_CPU_CM3_NVIC_ST_CTRL_INTEN 0x00000002 /* Interrupt enable. */
//#define OS_CPU_CM3_NVIC_ST_CTRL_ENABLE 0x00000001 /* Counter mode. */
os_cpu.c.c中需要注意到的地方差不多就是这些了。
下面是os_cpu_a.asm.这里面的东西最多了，也相对难理解，这就需要仔细看CM3权威指南这个资料了。
这是上面开关中断宏的汇编语言实现。
OS_CPU_SR_Save
MRS R0, PRIMASK ; Set prio int mask to mask all (except faults)
CPSID I
BX LR
OS_CPU_SR_Restore
MSR PRIMASK, R0
BX LR
启动最高优先级函数，只调用一次，在OSStart()中被调用。
;********************************************************************************************************
; START MULTITASKING
; void OSStartHighRdy(void)
;
; Note(s) : 1) This function triggers a PendSV exception (essentially, causes a context switch) to cause
; the first task to start.
;
; 2) OSStartHighRdy() MUST:
; a) Setup PendSV exception priority to lowest;
; b) Set initial PSP to 0, to tell context switcher this is first run;
; c) Set OSRunning to TRUE;
; d) Trigger PendSV exception;
; e) Enable interrupts (tasks will run with interrupts enabled).
;********************************************************************************************************
OSStartHighRdy
LDR R0, =NVIC_SYSPRI14 ; Set the PendSV exception priority
LDR R1, =NVIC_PENDSV_PRI
STRB R1, [R0]
MOVS R0, #0 ; Set the PSP to 0 for initial context switch call
MSR PSP, R0
LDR R0, =OSRunning ; OSRunning = TRUE
MOVS R1, #1
STRB R1, [R0]
LDR R0, =NVIC_INT_CTRL ; Trigger the PendSV exception (causes context switch)
LDR R1, =NVIC_PENDSVSET
STR R1, [R0]
CPSIE I ; Enable interrupts at processor level
OSStartHang
B OSStartHang ; Should never get here
主要是手动悬起PendSV中断，设置OSRunning为1，然后开启中断之后好进入PendSV中断处理函数中进行任务切换，开始运行ucosii。PendSV这个是需要掌握的，才能理解CM3是如何实现操作系统的管理的。
下面是两个任务切换函数，一个是任务级间切换，一个是中断与任务间切换，虽然代码相同，但意义不同，这主要就跟上面说道的PendSV中断有关了。因为这个中断的存在，我们的任务切换中实现的主要工作就是触发PendSV中断，让这个中断去处理任务切换相关细节。
;********************************************************************************************************
; PERFORM A CONTEXT SWITCH (From task level)
; void OSCtxSw(void)
;
; Note(s) : 1) OSCtxSw() is called when OS wants to perform a task context switch. This function
; triggers the PendSV exception which is where the real work is done.
;********************************************************************************************************
OSCtxSw
LDR R0, =NVIC_INT_CTRL ; Trigger the PendSV exception (causes context switch)
LDR R1, =NVIC_PENDSVSET
STR R1, [R0]
BX LR
;********************************************************************************************************
; PERFORM A CONTEXT SWITCH (From interrupt level)
; void OSIntCtxSw(void)
;
; Notes: 1) OSIntCtxSw() is called by OSIntExit() when it determines a context switch is needed as
; the result of an interrupt. This function simply triggers a PendSV exception which will
; be handled when there are no more interrupts active and interrupts are enabled.
;********************************************************************************************************
OSIntCtxSw
LDR R0, =NVIC_INT_CTRL ; Trigger the PendSV exception (causes context switch)
LDR R1, =NVIC_PENDSVSET
STR R1, [R0]
BX LR
下面就是非常重要的PendSV中断处理函数了。
;********************************************************************************************************
; HANDLE PendSV EXCEPTION
; void OS_CPU_PendSVHandler(void)
;
; Note(s) : 1) PendSV is used to cause a context switch. This is a recommended method for performing
; context switches with Cortex-M3. This is because the Cortex-M3 auto-saves half of the
; processor context on any exception, and restores same on return from exception. So only
; saving of R4-R11 is required and fixing up the stack pointers. Using the PendSV exception
; this way means that context saving and restoring is identical whether it is initiated from
; a thread or occurs due to an interrupt or exception.
;
; 2) Pseudo-code is:
; a) Get the process SP, if 0 then skip (goto d) the saving part (first context switch);
; b) Save remaining regs r4-r11 on process stack;
; c) Save the process SP in its TCB, OSTCBCur->OSTCBStkPtr = SP;
; d) Call OSTaskSwHook();
; e) Get current high priority, OSPrioCur = OSPrioHighRdy;
; f) Get current ready thread TCB, OSTCBCur = OSTCBHighRdy;
; g) Get new process SP from TCB, SP = OSTCBHighRdy->OSTCBStkPtr;
; h) Restore R4-R11 from new process stack;
; i) Perform exception return which will restore remaining context.
;
; 3) On entry into PendSV handler:
; a) The following have been saved on the process stack (by processor):
; xPSR, PC, LR, R12, R0-R3
; b) Processor mode is switched to Handler mode (from Thread mode)
; c) Stack is Main stack (switched from Process stack)
; d) OSTCBCur points to the OS_TCB of the task to suspend
; OSTCBHighRdy points to the OS_TCB of the task to resume
;
; 4) Since PendSV is set to lowest priority in the system (by OSStartHighRdy() above), we
; know that it will only be run when no other exception or interrupt is active, and
; therefore safe to assume that context being switched out was using the process stack (PSP).
;********************************************************************************************************
OS_CPU_PendSVHandler
CPSID I ; Prevent interruption during context switch
MRS R0, PSP ; PSP is process stack pointer
CBZ R0, OS_CPU_PendSVHandler_nosave ; Skip register save the first time
SUBS R0, R0, #0x20 ; Save remaining regs r4-11 on process stack
STM R0, {R4-R11}
LDR R1, =OSTCBCur ; OSTCBCur->OSTCBStkPtr = SP;
LDR R1, [R1]
STR R0, [R1] ; R0 is SP of process being switched out
; At this point, entire context of process has been saved
OS_CPU_PendSVHandler_nosave
PUSH {R14} ; Save LR exc_return value
LDR R0, =OSTaskSwHook ; OSTaskSwHook();
BLX R0
POP {R14}
LDR R0, =OSPrioCur ; OSPrioCur = OSPrioHighRdy;
LDR R1, =OSPrioHighRdy
LDRB R2, [R1]
STRB R2, [R0]
LDR R0, =OSTCBCur ; OSTCBCur = OSTCBHighRdy;
LDR R1, =OSTCBHighRdy
LDR R2, [R1]
STR R2, [R0]
LDR R0, [R2] ; R0 is new process SP; SP = OSTCBHighRdy->OSTCBStkPtr;
LDM R0, {R4-R11} ; Restore r4-11 from new process stack
ADDS R0, R0, #0x20
MSR PSP, R0 ; Load PSP with new process SP
ORR LR, LR, #0x04 ; Ensure exception return uses process stack
CPSIE I
BX LR ; Exception return will restore remaining context
END
下面的说的就是上面忽略的部分systick，作为操作系统的心脏，我们需要自己来组织这个中断。
在STM32库中的终端处理文件stm32f10x_it.c中有个Systick_Handler()函数，在里面添加处理。
/**
* @brief This function handles SysTick Handler.
* @param None
* @retval None
*/
void SysTick_Handler(void)
{
OSIntEnter();
OSTimeTick();
OSIntExit();
}
在主函数main.c中添加systick初始化函数
static void Systick_init(void)
{
RCC_ClocksTypeDef rcc_clocks;
RCC_GetClocksFreq(&rcc_clocks);
SysTick_Config(rcc_clocks.HCLK_Frequency / OS_TICKS_PER_SEC);
}
最后还有一个需要改动的就是要把STM32启动文件中的所有PendSV_Handler替换成OS_CPU_ PendSVHandler,因为UCOS默认移植文件中使用的是OS_CPU_ PendSVHandler。