1. Early CPU Initialization 2, enter the super user mode 3, empty instructions and data Cache4, empty the write fill buffer 5, configure and activate the memory controller 6, ensure that the interrupt is turned off and shielded (so even the interrupt source is present in the processor core Nor does not receive) 7, initialize all of the need to use the phase-locked loop and the time base (such as real time clock and system tick) 8, (optional) re-deploy the bootstile image to memory, restart the program You may directly initialize the running 9 in Flash, activate the Cache10, create and assemble the memory reserved area to share with the OS, these boot parameter districts can display system information 11, early plate initialization 12, install debug UART13, initialize the network card 14, _Start function It is the entrance to the boot program, which is also a function of the first run after the processor. It can effectively configure the CPU and other core logic units, which is a highly dependent hardware program. 15, turn off and mask the CPU level interrupt 16 ,
