July 30th Monday (七月　三十日　月曜日)

  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.