AIRCR：配置寄存器分组与自动复位控制


控制中断分组的是第8第9第10位。

如果要改变这三个位，要对16到31位写入0x05FA。#define AIRCR_VECTKEY_MASK 0x05FA0000就是这个意思了，
0x05fa对与AIRCR来说就是一个“入口钥匙”，只有对高16位写对了，才能对低16位写入。所以
AIRCR = AIRCR_VECTKEY_MASK | NVIC_PriorityGroup;
AIRCR = 0x05FA0000 | NVIC_PriorityGroup;
#define NVIC_PriorityGroup_2         ((uint32_t)0x500)
AIRCR = 0x05FA0000 | 0x500;



Access key; 0x05FA must be
written to this field to write to this
register, otherwise the write will
be ignored; the read-back value
of the upper half-word is 0xFA05
Indicates endianness for data: 1
for big endian (BE8) and 0 for little
endian; this can only change after
a reset