[PATCH rtems-docs v4] raspberrypi4.rst: Documentation for the new AArch64 Raspberry pi 4B BSP

[Kinsey Moore]

Looks good to me. Thanks for sticking with this!


Kinsey

On 10/7/2022 00:00, Mohd Noor Aman 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 | 111 +++++++++++++++++++++++++++++
>   user/bsps/bsps-aarch64.rst         |   1 +
>   2 files changed, 112 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..b36d47b
> --- /dev/null
> +++ b/user/bsps/aarch64/raspberrypi4.rst
> @@ -0,0 +1,111 @@
> +.. 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. ILP32 is not
> +supported. Raspberry pi 4B all variants and Raspberry Pi 400  are supported. The
> +default bootloader which is used by the Raspbian OS or other OS can be used to
> +boot RTEMS. SMP is currently not supported.
> +
> +Raspberry Pi 4B has 2 types of interrupt controller, GIC-400 (GICv2) and ARM
> +legacy generic controller. Both are supported. By default, raspberrypi 4B uses
> +ARM legacy generic controller. Set ``enable_gic=1`` in the ``config.txt`` file
> +to enable GIC.
> +
> +Clock Driver
> +------------
> +
> +The clock driver uses the `ARM Generic Timer`.
> +
> +Console Driver
> +--------------
> +
> +Raspberry pi 4B has 2 types of UARTs, ARM PL011 and Mini-uart. The PL011 is a
> +capable, broadly 16550-compatible UART, while the mini UART has a reduced
> +feature set. 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. Mini-uart is not supported.
> +
> +Preparing to boot
> +------------------
> +
> +Raspberry Pi uses a different mechanism to boot when compared with any ARM SoC.
> +First the GPU initializes, loads the bootloader (Raspberry pi firmware) and then
> +looks for the kernel img. This whole process is done by the GPU (VideoCore IV)
> +till the kernel is loaded. More information can be found on the `Raspberry pi
> +documentation page
> +<https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#boot-sequence>`_.
> +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`` file.
> +
> +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 and thus disabling the
> +default Mini-uart.
> +
> +.. code-block:: none
> +
> +  # if user wants to enable GIC, uncomment the next line
> +  # enable_gic=1
> +  arm_64bit=1
> +  dtoverlay = disable-bt
> +  enable_uart=1
> +
> +.. note::
> +  The Raspberry Pi 4B and 400 have an additional four PL011 UARTs. They are not
> +  supported.
> +
> +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