[PATCH rtems-docs] raspberrypi4.rst: Added Documentation for the new AArch64 Raspberry pi 4B BSP

[Noor Aman]

Here is the documentation patch. I've generated the output and it works
fine. Reviews are required.

Thanks,
Noor

On Mon, 26 Sept 2022 at 12:22, Mohd Noor Aman <nooraman5718 at gmail.com>
wrote:

> This patch adds the relevant documentations required for booting the new
> BSP. JTAG support is added for debugging. I have built the HTML docs and
> verified them.
> ---
>  user/bsps/aarch64/raspberrypi4.rst | 92 ++++++++++++++++++++++++++++++
>  user/bsps/bsps-aarch64.rst         |  1 +
>  2 files changed, 93 insertions(+)
>  create mode 100644 user/bsps/aarch64/raspberrypi4.rst
>
> diff --git a/user/bsps/aarch64/raspberrypi4.rst
> b/user/bsps/aarch64/raspberrypi4.rst
> new file mode 100644
> index 0000000..94daacf
> --- /dev/null
> +++ b/user/bsps/aarch64/raspberrypi4.rst
> @@ -0,0 +1,92 @@
> +.. SPDX-License-Identifier: CC-BY-SA-4.0
> +
> +.. Copyright (C) 2022 Mohd Noor Aman
> +
> +.. _BSP_aarch64_Raspberrypi_4:
> +
> +Raspberry Pi 4B
> +===============
> +
> +The 'raspberrypi4b' BSP currently supports only the LP64 ABI. Raspberry
> pi 4B
> +and Raspberry Pi 400  are supported. The default bootloader which is used
> by the
> +Raspbian OS or other OS can be used to boot the RTEMS. Currently, QEMU is
> not
> +supported. This BSP supports the GICv2 interrupt controller.
> +
> +Clock Driver
> +------------
> +
> +The clock driver uses the `ARM Generic Timer`.
> +
> +Console Driver
> +--------------
> +
> +The console driver supports the default Qemu emulated ARM PL011 PrimeCell
> UART
> +as well as the physical ARM PL011 PrimeCell UART in the raspberrypi
> hardware.
> +Only UART0 is supported as of now.
> +
> +Preparing to boot
> +------------------
> +
> +Raspberry Pi uses a different mechanism to boot. First the GPU
> initializes,
> +loads the bootloader and then looks for the kernel img. By default the
> arm64
> +mode looks for the ``kernel8.img``. Any other kernel can be loaded by
> adding
> +`kernel=<img_name>` to the ``config.txt``.
> +
> +The Firmware files are required in order to boot RTEMS. The latest
> firmware can
> +be downloaded from the `Raspberry Pi Firmware Repository
> +<https://github.com/raspberrypi/firmware/>`_. USB boot is supported. All
> the
> +files (Firmwares and kernel) must be place in the FAT32 partition only.
> Add
> +``arm_64bit=1`` in the config.txt file in order to boot the BSP in 64bit
> kernel
> +mode.
> +
> +
> +UART Setup
> +^^^^^^^^^^
> +
> +Connect your serial device to the GPIO15 and GPIO14. Add the following to
> the
> +config.txt file in order to use the PL011 UART0.
> +
> +.. code-block:: none
> +
> +  dtoverlay = disable-bt
> +  enable_uart=1
> +
> +Generating kernel image
> +^^^^^^^^^^^^^^^^^^^^^^^
> +
> +The following steps show how to run ``hello.exe`` on the BSP. Other
> executables
> +can be processed in a similar way.
> +
> +To create the kernel image:
> +
> +.. code-block:: shell
> +
> +  $ aarch64-rtems at rtems-ver-major@-objcopy -Obinary hello.exe kernel8.img
> +
> +Copy the kernel image to the SD card.
> +
> +JTAG Setup
> +----------
> +
> +The Raspberry Pi 4 doesn't have dedicated JTAG pins. Instead, you must
> configure
> +the GPIO pins (GPIO22-GPIO27) to activate the JTAG functionality. The RPi
> 4
> +documentation refers to this as Alt4 functions of those pins. Alt5 does
> exist
> +too, which goes from GPIO4, 5, 6, 12 and 13. you can check this out from
> +`pinout.xyz <https://pinout.xyz/pinout/jtag#>`_ or `eLinux
> +<https://elinux.org/RPi_BCM2835_GPIOs>`_
> +
> +One more thing to note on JTAG with Raspberry pi 4B is that, by default,
> All the
> +GPIO pins are pulled down, according to the `BCM2711 documentation
> +<https://datasheets.raspberrypi.com/bcm2711/bcm2711-peripherals.pdf>`_.
> This
> +wasn't the case in the earlier models. So in order to let the data flow
> freely,
> +we will have to disable them.
> +
> +.. code-block:: none
> +
> +  # Disable pull downs
> +  gpio=22-27=np
> +
> +  # Enable jtag pins (i.e. GPIO22-GPIO27)
> +  enable_jtag_gpio=1
> +
> +
> diff --git a/user/bsps/bsps-aarch64.rst b/user/bsps/bsps-aarch64.rst
> index 933370f..f3aa15c 100644
> --- a/user/bsps/bsps-aarch64.rst
> +++ b/user/bsps/bsps-aarch64.rst
> @@ -9,3 +9,4 @@ aarch64 (AArch64)
>  .. include:: aarch64/a72.rst
>  .. include:: aarch64/xilinx-versal.rst
>  .. include:: aarch64/xilinx-zynqmp.rst
> +.. include:: aarch64/raspberrypi4.rst
> \ No newline at end of file
> --
> 2.34.1
>
>
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