OS_CRITICAL_METHOD的意思

Method #1: Disable/Enable interrupts using simple instructions. After critical section, interrupts will be enabled even if they were disabled before entering the critical section.

 

Method #2: Disable/Enable interrupts by preserving the state of interrupts. In other words, if interrupts were disabled before entering the critical section, they will be disabled when leaving the critical section.

 

Method #3: Disable/Enable interrupts by preserving the state of interrupts. Generally speaking you would store the state of the interrupt disable flag in the local variable 'cpu_sr' and then disable interrupts. 'cpu_sr' is allocated in all of uC/OS-II's functions that need to disable interrupts. You would restore the interrupt disable state by copying back 'cpu_sr' into the CPU's status register

 

1）当OS_CRITICAL_METHOD= = 1时，简单实现如下：

#define   OS_ENTER_CRITICAL()   disable_int()

#define   OS_EXIT_CRITICAL()      enable_int()

但这样有一个问题，如果禁止中断的情况下调用uC/OS-II功能函数，那么从功能函数返回时，中断可能变成允许的了，而实际上还是希望是禁止的。

 

2）当OS_CRITICAL_METHOD= = 2时，实现如下：

#define OS_ENTER_CRITICAL() asm(“PUSH PSW”); asm(“DI”);

#define OS_EXIT_CRITICAL() asm(“POP PSW”);

执行OS_ENTER_CRITICAL()时，先将中断状态保存到堆栈，然后关中断；执行OS_EXIT_CRITICAL()时，再从堆栈中恢复原来的中断开/关状态。这种方法不会改变中断状态，避免前面的问题。

 

3）当OS_CRITICAL_METHOD= = 3时，实现如下：

#define OS_ENTER_CRITICAL() cpu_sr = get_processor_psw(); disable_interrupts();

#define OS_EXIT_CRITICAL() set_ processor_psw(cpu_sr);

将处理器状态字保存在局部变量中。