Tegra K1 boot sequence

Now I work with Jetson TK1. But Jetson is a finished product. I’m interested Tegra K1 boot sequence. What software boot first? For now, I know only about U-Boot, Linux Kernel… But when I make force recovery process, I press a force recovery button and something is booting in K1 processor and allows me to flash U-Boot. I’m wondering what is software doing this? This software already factory flashed when I bay only a Tegra K1 processor?

See this URL:
https://devtalk.nvidia.com/default/topic/979780/jetson-tx1/using-host-side-usb-3-0-xhci-driver-in-u-boot/post/5030933/#5030933

It all starts with “Tegra-boot”, (or just “tboot”). Tboot passes on to u-boot.

I don’t know if shipping Jetsons have had their initial version incremented since this all started, but my units all arrived with L4T R19.2 installed; there is an nVidia installer script to finalize the nVidia-provided components into the otherwise purely Ubuntu 14.04 sample rootfs (I think this would already be in place except for the need to accept the EULA first…segregating sample rootfs from nVidia components would likely have a licensing-related purpose).