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Raspberry Pi Bare Bones: Difference between revisions
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It worth mentioning that Pi 3 and 4 normally boots kernel8.img into 64 bit mode, but you can still use AArch32 with kernel7.img for backward compatibility. Note that in 64 bit mode, the boot code is loaded at 0x80000 and not 0x8000. The boot code in AArch64 is exactly the same for Pi 3 and 4, however Pi 4 has a different peripheral base address (see below the C example code).
With the latest firmware, only the primary core runs (core 0), and the secondary cores are awaiting in a spin loop. To wake them up, write a function's address at 0xE0 (core 1), 0xE8 (core 2) or 0xF0 (core 3) and they will start to execute that function.
The environment is set up and execution to _start transferred from [https://github.com/raspberrypi/tools/blob/master/armstubs/armstub8.S#L154 armstub8.s].
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