19.6.8 Boot ROM Phase Extension

On the cold-plugging attachment, the DSU sets the STATUSA.BREXTx bit which notifies the CPUx’s Boot ROM to wait until BREXTx clears before continuing the boot flow, where ‘x’ ranges from 0 to the number of CPUs. The debugger can write a ‘1’ to the BREXTx bit to clear the bit and end this phase extension.