Three ways for Cortex-M kernel to manage global interrupts

1. Use PRIMASK Register mask interrupt

usage ：PRIMASK Registers can be masked except NMI and HardFault All exceptions and interrupts except these two interrupts .
Program realization ：
<1> When using assembly , have access to CPS( Modify the processor state ) Instruction to modify PRIMASK The value of the register ：

	CPSIE I;    			// eliminate PRIMASK（ To interrupt ）
	CPSID I;    			// Set up PRIMASK（ No interruptions ）

<2>PRIMASK Registers can also be accessed through MRS and MSR Command access , as follows ：

	MOVS R0,	#1
	MSR PRIMASK,R0 ;	// take 1 write in PRIMASK Disable all interrupts 
 as well as ：
	MOVS R0,	#0
	MSR PRIMASK,R0 ;	// take 0 write in PRIMASK To enable all interrupts 

2. Use FAULTMASK Register mask interrupt

usage ：FAULTMASK Than PRIMASK stronger , It will raise the priority of the current exception to -1, So you can connect HardFault It's all blocked .FAULTMASK How to use and PRIMASK similar ,FAULTMASK It will be reset automatically when exiting .
Program realization ：
<1> When using assembly , have access to CPS( Modify the processor state ) Instruction to modify PRIMASK The value of the register ：

	CPSIE F;    		// eliminate FAULTMASK（ To interrupt ）
	CPSID F;    		// Set up FAULTMASK（ No interruptions ）

<2>FAULTMASK Registers can also be accessed through MRS and MSR Command access , as follows ：

	MOVS R0,	#1
	MSR FAULTMASK,R0 ;	// take 1 write in FAULTMASK Disable all interrupts 
 as well as ：
	MOVS R0, 	#0
	MSR FAULTMASK,R0 ;	// take 0 write in FAULTMASK To enable all interrupts 

3. Use BASEPRI Register mask interrupt

usage ：FAULTMASK and PRIMASK Register is directly closed except reset ,NMI,HardFault All other interrupts except , But in some cases, it is necessary to control the interrupt shielding more finely , For example, only interrupts with priority lower than a certain threshold are screened . This threshold priority is stored in the register BASEPRI in , towards BASEPRI Write 0 Will stop shielding interrupt .
such as , The priority of shielding should not be higher than 0x50 The interrupt , You can use the following assembly instructions ：

	MOVS R0,	#0x50
	MSR BASEPRI,R0 

If you need to cancel BASEPRI Shielding of interrupts , You can use the following code ：

	MOVS R0,	#0
	MSR BASEPRI,R0