Boot Principle Analysis of ARM9

When ARM system is power-on or reset,program will run from the address 0x0.And booting from devices needs to map devices to address 0x0.But different ARM chips manufacturers have different mapping modes.The case in point is AT91RM9200 of ATEML,which may select the internal integrated ROM or the external chip linked to NCS0 as boot device via boot model select.The internal boot runs the integrated program,the external boot takes bootloader u-boot as an example.