BootX calling into OF code can be found in ci.c sl_words.c sets up a "pseudo-device" that provides some services for the sl (secondary loader) there is a huge pile of forth there that I don't understand that well the InitEverything function in main.c also seems to run a lot of important initialization (obviously) OF calls but most notably that of the keyboard, stdout, and memory map (main.c:223-241, 248-272) reserve memory check/read keyboard several things: in the sl_words package, there is defined a "keymap" interface InitKeyMap (ci/sl_words.c:212) returns the address of a char array that represents what keys are down when the function UpdateKeyMap (ci/sl_words.c:224) is called. TestForKey is an example of how to use this key down vector (sl/main.c:765). It only tests specific keys used during mac os x booting. print to console ci_io.c contains: int putchar(int ch) this function uses sl_words, specifically sl_emit, to output characters copy device tree sl/device_tree.c This is kind of strange... apparently the OF CI call "Peer" (ci.c:57) called with the argument 0 (device_tree.c:50) produces the root of the device tree. memory BootX and the Kernel seem to live in between gImageFirstBootXAddr claiming memory in OF there is a CI function called claim (ci.c:471) examples of its use: main.c:302, 308, 315 // Claim takes a virt address, a size, and an alignment. // It return baseaddr or -1 for claim failed. note that claim is broken on 2.x and lower versions of OF, we're using 3 so we can rest easy BootX also sets properties of the mmap device, which from the comments seems to add things to the memory map, in AllocateMemoryRange(main.c:1104). this gets used in the boot args setup (main.c:444)