diff --git a/RPI-BUILD.md b/RPI-BUILD.md new file mode 100644 index 0000000..e0cb82c --- /dev/null +++ b/RPI-BUILD.md @@ -0,0 +1,43 @@ +Writing a "bare metal" operating system for Raspberry Pi 4 +========================================================== + +Building on the RPi4 itself +--------------------------- + +It's possible (but not super-simple) to follow this tutorial on the Raspberry Pi without need for an additional build device. + +It will require you firstly to re-image your Pi to use the 64-bit Raspberry Pi OS (Beta): + + * Download a zipped _.img_ image file from the [64-bit image list](https://downloads.raspberrypi.org/raspios_arm64/images/), picking the newest update + * Unzip it and use the [Raspberry Pi Imager](https://www.raspberrypi.org/software/) to write it to your SD card, selecting "Use custom" from the options and pointing it at your downloaded _.img_ file + * Boot the Pi and follow the setup wizard to ensure you have a working Internet connection + * Just for luck, run `sudo apt update` + +You'll then need to download a cross-compiler from the Arm website. + +What you're looking for is the current [AArch64 ELF bare-metal target (aarch64-none-elf)](https://developer.arm.com/-/media/Files/downloads/gnu-a/10.2-2020.11/binrel/gcc-arm-10.2-2020.11-aarch64-aarch64-none-elf.tar.xz). If this link is somehow broken, you can use Google to search for "Arm GNU-A linux hosted cross compilers". + +Then unpack the archive using `tar -xf _downloaded-filename_`. You'll end up with a _gcc_ directory (albeit with a slightly longer name), which itself contains a _bin_ subdirectory, wherein you'll find the _gcc_ executable (again - with a longer name!). Remember this path. + +Now let's build something: + + * Use `git` to clone this repo: `git clone https://github.com/isometimes/rpi4-osdev.git` + * Decide which part you want to build - I like testing with _part5-framebuffer_ (it's visual, so you'll know when it works!) + * Copy the _Makefile.gcc_ to _Makefile_ + * Edit the _Makefile_ and ensure the `GCCPATH` variable points to the _bin_ subdirectory that you just unpacked + * Type `make` at the command line and it should build without errors + +If you want to then boot with this, you'll need to copy the _kernel8.img_ file to a prepped SD card as the tutorial discusses. For the purposes of testing this process, I did the following (NOTE: it will trash your OS install unless you backup the old files so you can move them back later): + + * `sudo cp kernel8.img /boot` + * Then edit _/boot/config.txt_ to include only these lines (for _part5-framebuffer_ anyway, read the tutorial in full for any necessary config changes for other parts): + +```c +hdmi_group=1 +hdmi_mode=16 +core_freq_min=500 +``` + +Reboot and you should see the part5-framebuffer demo firing up! + +[Go to part1-bootstrapping >](./part1-bootstrapping/)