Technical Q&A HW88

The "chosen" node in the device tree

Q: What is the "chosen" node in the device tree?

A: Per IEEE 1275 Section 3.5 Standard System Nodes, the /chosen node contains parameters chosen or specified at runtime. Here is an example of that node on a G3 using the Open Firmware user interface, OFUI.

0 > dev /chosen pwd .properties /chosen
name                     chosen
stdin                    ff9cf340
stdout                   ff9cf280
memory                   ff9dd680
mmu                      ff9dd700
nvram                    ff9d3400
bootpath                 00
bootargs                 00
mac-address              00050231 2913
interrupt-controller     ff861220

Let's look at two properties. Stdin is the standard input for the OFUI and the value ff9cf340 is the phandle for that node. Not very interesting. Mac-address, on the other hand, is the media access control, mac, and hardware ID for the machine. If you use the Apple System Profiler, you will find this address in the Network Overview section under the AppleTalk subheading. A little more interesting.