>"The Raspberry Pi line of single-board computers runs ThreadX as a binary blob on the graphics processing unit (GPU). This controls initial booting, which in turn is used to boot secondary operating systems such as Linux, and continues to operate in a more privileged role even after the boot process.[12]"
https://github.com/azure-rtos/threadx/
https://en.wikipedia.org/wiki/ThreadX
>"The Raspberry Pi line of single-board computers runs ThreadX as a binary blob on the graphics processing unit (GPU). This controls initial booting, which in turn is used to boot secondary operating systems such as Linux, and continues to operate in a more privileged role even after the boot process.[12]"