今天看porteus官网，对M3内核支持还不完善啊

l6931639

The following is a listing of known limitations in the current version of the ARM® Cortex™-M3:

• Bitband alias regions are of type XN (Execute Never).
• Cache information is not used.
• Systick calibration value register (SYST_CALIB) is ignored.
• Data Barrier instructions (DMB,DSB) are treated as NOP.
• Register PLLCFG is not modelled.
• Clock Verification Timers and Internal brown-out detector not modelled.
• Registers DR2R,DR4R,DR8R,SLR are not modelled.
• Loopback feature of the I2C Module is not documented and therefore not modelled.