关于M4的CONTROL寄存器

shibinjie

求教大神，M4如果开启了FPU后,那么CONTROL[2]这一位是一直为1吗？还是有时也会为0？

eric2013

开启了不行，得使用了相应浮点指令才会被置位

权威指南中的说明是这样的
FPCA bit in the CONTROL register: CONTROL.FPCA indicates if the current context (e.g., task) has a floating point operation. It is:
• Set to 1 when the processor executes a floating point instruction
• Cleared to zero at the beginning of an exception handler
• Set to the inverse of bit 4 in EXC_RETURN at exception return
• Cleared to zero after a reset

shibinjie

eric2013:开启了不行，得使用了相应浮点指令才会被置位

权威指南中的说明是这样的
FPCA bit in the CONTROL register: CONTROL.FPCA indicates if the current context (e.g., task) has a floating point operation. It is:
• Set to 1 when the processor executes a floating poi .. (2017-07-15 17:07) 

[s:151]，看来还是得多看权威指南