1 Reset -3 (Highest) Reset
绝大部分处理器设计时，将复位中断放在最高优先级。
一般来说这样设计是合理的，个人认为在某些应用场景这样处理仍有局限性。
2 NMI -2 Nonmaskable interrupt
The NMI is similar to IRQ, but it cannot be disabled and has the highest priority apart from the
reset. It is very useful for safety critical systems like industrial control or automotive.
Depending on the design of the microcontroller, the NMI could be used for power failure
handling, or it can be connected to a watchdog unit to restart a system if the system stopped
responding. Because the NMI cannot be disabled by control registers, the responsiveness is
guaranteed.
官方描述NMI是为了在工控和车控产品领域，专为提高安全性的设计。
也就是说安全第一：把安全性放在最高优先级处理，除了复位以外，不准许任何其他中断能够打断安全处理程序。
通常设计处理是：电源异常处理，连接看门狗去复位系统
3 Hard fault -1 Fault handling exception
Hard fault is an exception type dedicated to handling fault conditions during program
execution. These fault conditions can be trying to execute an unknown opcode, a fault on a bus
interface or memory system, or illegal operations like trying to switch to ARM state.
硬件错误：通常指执行未知操作指令，总线错误，内存错误等等。
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