See the top level README file for more information on documentation and how to run these programs. So for my pi3, the MPIDR_EL1 register lower 2 bits indicate which core. So I sort the cores out and have them each do something different. As with other examples in this directory you have to not only have a kernel7.img (uart03.bin in this case) but you have to have config.txt arm_control=0x200 kernel_old=1 disable_commandline_tags=1 http://elinux.org/RPiconfig describes each of these arm_control=0x200 processor in 64 bit mode kernel_old=1 load kernel7.img to 0x0000 instead of 0x8000 disable_commandline_tags=1 do not write over my program with atags