__enable_irq() 对应的汇编代码是 : CPSIE I
这是个特权级的指令,如果在用户态执行,将被忽略(不起作用)
CPS<effect><q> <iflags>
where:
<effect> Specifies the effect required on PRIMASK and FAULTMASK. This is one of:
IE Interrupt Enable. This sets the specified bits to 0.
ID Interrupt Disable. This sets the specified bits to 1.
<q> See Standard assembler syntax fields on page A7-207. A CPS instruction must be
unconditional.
<iflags> Is a sequence of one or more of the following, specifying which masks are affected:
i PRIMASK. Raises the execution priority to 0 when set to 1. This is a 1-bit
register, that supports privileged access only.
f FAULTMASK. Raises the execution priority to -1 (the same as HardFault)
when it is set to 1.
Operation
EncodingSpecificOperations();
if CurrentModeIsPrivileged() then
if enable then
if affectPRI then PRIMASK<0> = ‘0’;
if affectFAULT then FAULTMASK<0> = ‘0’;
if disable then
if affectPRI then PRIMASK<0> = ‘1’;
if affectFAULT && ExecutionPriority() > -1 then FAULTMASK<0> = ‘1’;
Exceptions
None.
Notes
Privilege Any unprivileged code attempt to write the masks is ignored.
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