Raspberry Pi 2 Model B Bare Metal Reference Design

Question

I've been searching the web for the past day and I must just not know where to look. I can find bare metal examples for the Raspberry Pi (1) and the Raspberry Pi 3, but I have been unable to find any blogs, posts, forums, etc that have references for bare metal examples for the Raspberry Pi 2.

I went so far as to try building the Raspberry Pi reference design I found, but regardless of what I did after building it, I couldn't get my Raspberry Pi 2b to actually boot it.

Just in case there's confusion, I'm not looking to boot Linux, but rather to create a simple few lines of code to just flash the LED. If I can do this, I can expand to whatever I want since i'll know how to get the bootloader (in the GPU) to work for me.

I'm a NOOB with the Raspberry Pi, but I've been doing embedded systems for a long time. If there's anyone out there that can point me to the right place, I know I can figure it out.

Thanks in advance for any and all suggestions.

shabaz · Answer

Hi Brett, There is a wikibook for it here: https://en.wikibooks.org/wiki/Bare-metal_Raspberry_Pi_Programming I can understand it for academic purposes, but otherwise bare metal on the Pi is likely to end up vastly under-using the Pi, and doesn't easily allow the use of libraries of code (that rely on Linux being the OS). The chip on the Pi is designed to run an OS (as opposed to a microcontroller which of course can still run an OS, but has hardware facilities/resources designed for smaller OSs or bare-metal. If you wish to flash an LED in assembler or in C code, that is possible under Linux too. If you're looking for real-time behavior, that is just as easy or just as difficult bare-metal, as it is under Linux. Anyway, it is certainly feasible to go bare-metal on the Pi if you wish. There is also a combined bare-metal and assember forum, there seem to be posts regarding tutorials on bare-metal: https://www.raspberrypi.org/forums/viewforum.php?f=72&sid=12f91dca053fc05f8a82644c6ed66099

Gough Lui · Answer

Whoops - sorry, copy and pasted the wrong link: https://github.com/dwelch67/raspberrypi/tree/master/boards/pi2 That's probably the one you need - Gough

rew · Answer

Hi Brett, The "rpidmx512" project is bare-metal and works on raspberry pi 2. So google for the term download the sources and look around. There are also prebuilt images, so that you can test the code to eliminate "compiler issues".

Gough Lui · Answer

Not sure if this is what you are after, but perhaps give this one a go: https://github.com/dwelch67/raspberrypi/tree/master/blinker02

Gough Lui · Answer

Dear Brett,

No specific hints, but I saw that the latest commits by dwelch67 referenced the pi2:

thanks to ultimo and others I think I have the pi2 switching back to …

…svc and secure mode now.

and other cleanup

I checked the file changes and stumbled upon the /boards/pi2 area which gave away the location which was where the previous example's README should have pointed to, along with the /SVC subdirectory where pi2-specific versions of the examples reside. The diff shows the changes, I presume, from the previous pi2 code which probably had the pi2's CPU running in a different mode.

- Gough