单片机中的WFI/WFE指令

进入低功耗模式的两个指令，这是ARM里CMSIS内核中的指令。详情请参考链接里大神们的讨论链接http://www.wowotech.net/armv8a_arch/wfe_wfi.html

cmsis_arm.cc里有如下说明

/**
brief Wait For Interrupt
details Wait For Interrupt is a hint instruction that suspends execution until one of a number of events occurs.
*/
#define __WFI __wfi

/**
brief Wait For Event
details Wait For Event is a hint instruction that permits the processor to enter
a low-power state until one of a number of events occurs.
*/
#define __WFE __wfe

什么意思呢？简单的说：

WFI进入则可由任意中断唤醒

WFE进入则由事件唤醒

WFI = wait for interrupt 等待中断，即下一次中断发生前都在此hold住不干活
WFE = wait for event 等待事件，即下一次事件发生前都在此hold住不干活
执行这两条语句后CPU功耗会降低，通常用这两条语句来省电。