On Sunday 06 Oct 2013, Amalinda J' Gamage wrote: > I am a new user to beaglebone and I have a couple of basic questions. > I want to know what is meant by DT or Device tree overlay and why it is > required for BB/ ARM335X. Is it not required for other main processors like > Intel because they are " defined" in the Linux kernel? and TI ARM3358 > processor is not " defined" . What support is available for other > "popular" processors and is not available for TI ARM 3358 in Linux Kernal? > Or was there support BEFORE and was it taken BACK? > I mean is this the reason that we make a device tree and pass it to the > system ? I may have mentioned incorrect statements please feel free to > correct me. For a start its not just the 3358/9 that use device tree. It started with PowerPC chips, has spread to all ARM chips and is now spreading to MIPS chips. The 3358/9 chips are defined in the kernel and are fully supported.
The x86 and AMD64 chips have as others have mentioned busses that are more self identifying - such as PCI. However just look at the lmsensors code to see that there are many chips which provide things like thermal and voltage sensing which have to be found by implication rather than identification. ACPI also comes into this equation, but does not exist on ARM. Linus Torvalds got fed up with the previous way of handing ARM chips and boards, and so the ARM community used the device tree to get rid of the mess. However there was a lot of mess, and so converting everything to use the device trees is taking a bit of time and getting in the way of new development as there are only a limited number of developers. You can find details about device tree at http://www.devicetree.org which will give you the history and the links to OpenFirmware which is the real origin of device trees. > > secondly, I know that with no Device tree stuff, it is possible to lighten > up an LED connected to the BB and BBB using the terminal. So if the > definitions are not there in the Linux kernel, how come this method works? > I mean how can one export a GPIO and lighten the LED connected if that is > not found in the kernel? If so, then is a DT necessary at all? Most people want to rather more than just light up a LED. > > A confused. David -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
