ucos在mdk上怎么没定义cpu_sr

/*
*********************************************************************************************************
*                                              Cortex-M1
*                                      Critical Section Management
*
* 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.
*             NOT IMPLEMENTED
*
* 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.
*             NOT IMPLEMENTED
*
* 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.
*********************************************************************************************************
*/

#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