Purpose of the 'magic' number in eeprom?

[Adam Lee]

Hello, I noticed the magic number "0xEE3355AA" at the offset[0:4] in the eeprom of Beaglebone.
What is the purpose of this data? Is it merely to tell if the board ID structure has been tempered?

[Jason Kridner]

U-boot uses it to identify the board as a BeagleBone.

In particular, if you look in the source here:

http://git.denx.de/?p=u-boot.git;a=blob;f=board/ti/am335x/board.c;h=0739e6021a21e71d7d0f5c840b793ce7fdf98fae;hb=f33cdaa4c3da4a8fd35aa2f9a3172f31cc887b35#l63

You'll see where the header is read. This says that we can likely
trust the contents of the EEPROM to tell us the type of board.

The idea here is that people might want to use BeagleBone as a
reference to make their own boards. This makes it relatively easy. If
you use your own u-boot, you can simply remove the EEPROM, but we try
to use the same source and binary as a bunch of other similar boards.
This binary compatibility allows for bootable SD card images to be
shared between such boards.

We left a bunch of room in the EEPROM for potentially storing a bunch
of other configuration information. So far, not there hasn't been any
consolidated and compelling suggestions for its use. Personally, I
wanted a configuration tool to store some info for boot, but defining
the format and authoring tool has proven difficult for now. So, you
can use it as you wish.

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