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110 lines
3.7 KiB
ReStructuredText
110 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 2022 Mohd Noor Aman
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.. _BSP_aarch64_Raspberrypi_4:
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Raspberry Pi 4B
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===============
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The 'raspberrypi4b' BSP currently supports only the LP64 ABI. ILP32 is not
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supported. Raspberry pi 4B all variants and Raspberry Pi 400 are supported. The
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default bootloader which is used by the Raspbian OS or other OS can be used to
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boot RTEMS. SMP is currently not supported.
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Raspberry Pi 4B has 2 types of interrupt controller, GIC-400 (GICv2) and ARM
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legacy generic controller. Both are supported. By default, raspberrypi 4B uses
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ARM legacy generic controller. Set ``enable_gic=1`` in the ``config.txt`` file
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to enable GIC.
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Clock Driver
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------------
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The clock driver uses the `ARM Generic Timer`.
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Console Driver
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--------------
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Raspberry pi 4B has 2 types of UARTs, ARM PL011 and Mini-uart. The PL011 is a
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capable, broadly 16550-compatible UART, while the mini UART has a reduced
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feature set. The console driver supports the default Qemu emulated ARM PL011
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PrimeCell UART as well as the physical ARM PL011 PrimeCell UART in the
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raspberrypi hardware. Mini-uart is not supported.
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Preparing to boot
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------------------
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Raspberry Pi uses a different mechanism to boot when compared with any ARM SoC.
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First the GPU initializes, loads the bootloader (Raspberry pi firmware) and then
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looks for the kernel img. This whole process is done by the GPU (VideoCore IV)
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till the kernel is loaded. More information can be found on the `Raspberry pi
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documentation page
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<https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#boot-sequence>`_.
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By default the arm64 mode looks for the ``kernel8.img``. Any other kernel can be
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loaded by adding ``kernel=<img_name>`` to the ``config.txt`` file.
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The Firmware files are required in order to boot RTEMS. The latest firmware can
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be downloaded from the `Raspberry Pi Firmware Repository
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<https://github.com/raspberrypi/firmware/>`_. USB boot is supported. All the
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files (Firmwares and kernel) must be place in the FAT32 partition only. Add
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``arm_64bit=1`` in the ``config.txt`` file in order to boot the BSP in 64bit
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kernel mode.
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UART Setup
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^^^^^^^^^^
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Connect your serial device to the GPIO15 and GPIO14. Add the following to the
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``config.txt`` file in order to use the PL011 UART0 and thus disabling the
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default Mini-uart.
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.. code-block:: none
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# if user wants to enable GIC, uncomment the next line
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# enable_gic=1
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arm_64bit=1
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dtoverlay = disable-bt
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enable_uart=1
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.. note::
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The Raspberry Pi 4B and 400 have an additional four PL011 UARTs. They are not
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supported.
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Generating kernel image
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^^^^^^^^^^^^^^^^^^^^^^^
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The following steps show how to run ``hello.exe`` on the BSP. Other executables
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can be processed in a similar way.
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To create the kernel image:
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.. code-block:: shell
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$ aarch64-rtems@rtems-ver-major@-objcopy -Obinary hello.exe kernel8.img
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Copy the kernel image to the SD card.
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JTAG Setup
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----------
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The Raspberry Pi 4 doesn't have dedicated JTAG pins. Instead, you must configure
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the GPIO pins (GPIO22-GPIO27) to activate the JTAG functionality. The RPi 4
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documentation refers to this as Alt4 functions of those pins. Alt5 does exist
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too, which goes from GPIO4, 5, 6, 12 and 13. you can check this out from
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`pinout.xyz <https://pinout.xyz/pinout/jtag#>`_ or `eLinux
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<https://elinux.org/RPi_BCM2835_GPIOs>`_
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One more thing to note on JTAG with Raspberry pi 4B is that, by default, All the
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GPIO pins are pulled down, according to the `BCM2711 documentation
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<https://datasheets.raspberrypi.com/bcm2711/bcm2711-peripherals.pdf>`_. This
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wasn't the case in the earlier models. So in order to let the data flow freely,
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we will have to disable them.
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.. code-block:: none
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# Disable pull downs
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gpio=22-27=np
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# Enable jtag pins (i.e. GPIO22-GPIO27)
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enable_jtag_gpio=1
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