doc/raspberrypi: Added instructions for raspberrypi

Added instructions to run examples on raspberrypi.

user/bsps/arm/raspberrypi.rst

@@ -5,4 +5,113 @@
 raspberrypi
 ===========
 
-TODO.
+This BSP supports `Raspberry Pi 1` and `Raspberry Pi 2` currently.
+The support for `Raspberry Pi 3` is work under progress.
+The default bootloader on the Raspberry Pi which is used to boot Raspbian
+or other OS can be also used to boot RTEMS. U-boot can also be used.
+
+Setup SD card
+----------------
+
+The Raspberry Pis have an unconventional booting mechanism. The GPU
+boots first, initializes itself, runs the bootloader and starts the CPU.
+The bootloader looks for a kernel image, by default the kernel images must
+have a name of the form ``kernel*.img`` but this can be changed by adding
+`kernel=<img_name>` to ``config.txt``.
+
+You must provide the required files for the GPU to proceed. These files
+can be downloaded from
+`the Raspberry Pi Firmware Repository <https://github.com/raspberrypi/firmware/tree/master/boot>`_.
+You can remove the ``kernel*.img`` files if you want too, but don't touch
+the other files.
+
+Copy these files in to a SD card with FAT filesystem.
+
+Kernel image
+------------
+
+The following steps show how to run ``hello.exe`` on a Raspberry Pi 2.
+The same instructions can be applied to Raspberry Pi 1 also.
+Other executables can be processed in a similar way.
+
+To create the kernel image:
+
+.. code-block:: none
+
+     $ arm-rtems5-objcopy -Obinary hello.exe kernel.img
+
+Copy the kernel image to the SD card.
+
+Make sure you have these lines below, in your ``config.txt``.
+
+.. code-block:: none
+
+     enable-uart=1
+     kernel_address=0x200000
+     kernel=kernel.img
+
+Testing using QEMU
+------------------
+
+QEMU can be built using RSB. Navigate to ``<SOURCE_BUILDER_DIR>/rtems``
+and run this command.
+
+.. code-block:: none
+
+     $ ../source-builder/sb-set-builder --prefix=<TOOLCHAIN_DIR> devel/qemu4.bset
+
+**Note**: Replace ``<SOURCE_BUILDER_DIR>`` and ``<TOOLCHAIN_DIR>`` with the
+correct path of the directories. For example, if you used quick-start section
+as your reference, these two will be ``$HOME/quick-start/src/rsb`` and
+``$HOME/quick-start/rtems/5`` respectively,
+
+QEMU along with GDB can be used for debugging, but it only supports
+Raspberry Pi 2 and the emulation is also incomplete. So some of the
+features might not work as expected.
+
+Make sure your version of QEMU is newer than v2.6, because older ones don't
+support Raspberry Pis.
+
+.. code-block:: none
+
+     $ qemu-system-arm -M raspi2 -m 1G -kernel hello.exe -serial mon:stdio -nographic -S -s
+
+This starts QEMU and creates a socket at port ``localhost:1234`` for GDB to
+connect.
+
+The Device Tree Blob (DTB) is needed to load the device tree while starting up
+the kernel. The BSP uses information from this file to initialize the drivers.
+
+Make sure you pass in the correct DTB file. There are currently two version of
+DTB for the Raspberry Pi 2 ``bcm2709-rpi-2-b.dtb`` and ``bcm2710-rpi-2-b.dtb``.
+The ``bcm2709-rpi-2-b.dtb`` is for Raspberry Pi 2 Model B and
+``bcm2710-rpi-2-b.dtb`` is for Raspberry Pi 2 Model B v1.2
+
+We need to pass in the DTB file to GDB before running the example.
+
+In a new terminal, run GDB using
+
+.. code-block:: none
+
+     $ arm-rtems5-gdb hello.exe
+
+This will open GDB and will load the symbol table from hello.exe. Issue the
+following commands in the GDB prompt.
+
+.. code-block:: none
+
+     (gdb) tar remote:1234
+     (gdb) load
+     (gdb) restore bcm2709-rpi-2-b.dtb binary 0x2ef00000
+     (gdb) set $r2 = 0x2ef00000
+
+This will connect GDB to QEMU and will load the DTB file and the application.
+
+.. code-block:: none
+
+     (gdb) continue
+
+The ``continue`` command will run the executable.
+
+**Note**: Add ``set scheduler-locking on`` in GDB if you have any issues
+running the examples.