本文介绍了ARM处理器在启动时的状态及如何使用BX指令在ARM状态和Thumb状态间进行切换。当遇到异常情况如IRQ、FIQ等时，系统会自动返回到相应状态。
When ARM chip startting up, it should be at ARM status.
To switch Thumb status: when the operand register 0 bit is 1, can use "BX" instruction, switch to Thumb status
from ARM status. Besides when being at exceptions (such as, IRQ, FIQ, Undef, Abort, SWI, etc) at Thumb status,
return from those exceptions, enter Thumbe status automatically.
To switch ARM status: when the operand register 0 bit is 0, can use "BX" instruction, switch to ARM status
from Thumb status. Besides when being at exceptions (such as, IRQ, FIQ, Undef, Abort, SWI, etc) at ARM status,
return from those exceptions, enter ARM status automatically.
To switch Thumb status: when the operand register 0 bit is 1, can use "BX" instruction, switch to Thumb status
from ARM status. Besides when being at exceptions (such as, IRQ, FIQ, Undef, Abort, SWI, etc) at Thumb status,
return from those exceptions, enter Thumbe status automatically.
To switch ARM status: when the operand register 0 bit is 0, can use "BX" instruction, switch to ARM status
from Thumb status. Besides when being at exceptions (such as, IRQ, FIQ, Undef, Abort, SWI, etc) at ARM status,
return from those exceptions, enter ARM status automatically.
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