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Fixes and improvements to Raspberry Pi 4B documentation #203

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merged 5 commits into from
Oct 18, 2023
Merged

Fixes and improvements to Raspberry Pi 4B documentation #203

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4f307f9
Name the Raspberry Pi 4B consistently
Ivan-Velickovic Oct 18, 2023
86156ad
Various fixes and improvements to RPi4 docs
Ivan-Velickovic Oct 18, 2023
a388c56
Mention default RPi4 model seL4 builds for
Ivan-Velickovic Oct 18, 2023
1935cbd
Link to specific binaries in RPi4 setup
Ivan-Velickovic Oct 18, 2023
6f59737
Improve RPi4 U-Boot instructions
Ivan-Velickovic Oct 18, 2023
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92 changes: 43 additions & 49 deletions Hardware/Rpi4.md
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
---
arm_hardware: true
cmake_plat: rpi4
xcompiler_arg: -DAARCH64=1
platform: Raspberry Pi 4-b
xcompiler_arg: -DAARCH64=1 -DRPI4_MEMORY=<1024,2048,4096,8192>
platform: Raspberry Pi 4B
arch: ARMv8A
virtualization: ARM HYP
iommu: "No"
Expand All @@ -15,82 +15,76 @@ SPDX-License-Identifier: CC-BY-SA-4.0
SPDX-FileCopyrightText: 2020 seL4 Project a Series of LF Projects, LLC.
---

# Raspberry PI 4 Model B
# Raspberry Pi 4 Model B

## Serial connection
Serial TX and RX are located at GPIO pins 14 and 15 respectively
Serial TX and RX are located at GPIO pins 14 and 15 respectively.

## U-Boot

Right now, the default U-Boot will not successfully boot an seL4 image
on the RPi4 because of cache configuration issues in the seL4
ELFLoader. This problem can be remedied by having U-boot disable caches
before loading seL4. Unfortunately, the stock upstream U-boot used to
disable caches before loading the kernel image, but as of this patch
(<https://github.com/u-boot/u-boot/commit/995eab8b5b580b67394312b1621c60a71042cd18>),
U-boot no longer disables caches.

In order to obtain a U-boot binary that disables caching, you should
compile U-Boot from source yourself.
You can do this by cloning U-boot from upstream,
then reverting commit 995eab8b5b580b67394312b1621c60a71042cd18, and then
building it:
In order to build U-Boot for the Raspberry Pi 4B, run the following commands:
```bash
git clone https://github.com/u-boot/u-boot.git u-boot
cd u-boot
git revert 995eab8b5b580b67394312b1621c60a71042cd18
make CROSS_COMPILE=aarch64-linux-gnu- rpi_4_defconfig
make CROSS_COMPILE=aarch64-linux-gnu-
```

This will enable you to get the most up-to-date U-boot which will boot
seL4 on the RPi4 successfully.

**NOTE:** Automatic revert is not going to work if you are using the
latest version of u-boot. You need to manually revert the change by
looking at the changeset.
In the `u-boot` directory you should now see the U-Boot image `u-boot.bin` indicating that U-Boot has successfully compiled.

More information regarding U-Boot support for the Raspberry Pi can be found [here](https://u-boot.readthedocs.io/en/latest/board/broadcom/raspberrypi.html).

## SD card setup
The PI boots from the first FAT32 partition on the
SD card. Where files are specified, they should be located in the root
directory of this partition.
The RPi4 boots from the first FAT32 partition on the microSD card. Where files are specified,
they should be located in the root directory of this partition.

|Stage |Filename |Description |Source|
|-|-|-|-|
|FSBL |- |Mounts SD and loads SSBL |ROM |
|SSBL |bootcode.bin|Loads GPU firmware and boots GPU|<https://github.com/raspberrypi/firmware/tree/master/boot> |
|GPU firmware |start4.elf |Loads CPU bootloader and boots CPU |<https://github.com/raspberrypi/firmware/tree/master/boot> |
|Usually the Linux kernel, but could also be u-boot |u-boot.bin |u-boot| Compiled using the instructions above |
||config.txt|u-boot parameters |Add `arm_64bit=1`, `kernel=u-boot.bin`, and `dtoverlay=disable-bt` to the bottom of config.txt |
||uboot.env |u-boot saved environment |Generated by u-boot (default environment) bootcmd copied to bootcmd_orig bootcmd and bootdelay removed |
||bcm2711-rpi-4-b.dtb | RPi4 device tree blob |<https://github.com/raspberrypi/firmware/tree/master/boot> |
|SSBL |bootcode.bin|Loads GPU firmware and boots GPU|<https://github.com/raspberrypi/firmware/tree/master/boot/bootcode.bin> |
|GPU firmware |start4.elf |Loads CPU bootloader and boots CPU |<https://github.com/raspberrypi/firmware/tree/master/boot/start4.elf> |
|Usually the Linux kernel, but could also be U-Boot |u-boot.bin |U-Boot binary| Compiled using the instructions above |
||config.txt|U-Boot parameters |Add `arm_64bit=1`, `kernel=u-boot.bin`, and `dtoverlay=disable-bt` to the bottom of `config.txt` |
||uboot.env |U-Boot saved environment |Generated by U-Boot (default environment) bootcmd copied to bootcmd_orig bootcmd and bootdelay removed. This file will not exist when you first setup your SD card. |
||bcm2711-rpi-4-b.dtb | RPi4 device tree blob |<https://github.com/raspberrypi/firmware/tree/master/boot/bcm2711-rpi-4-b.dtb> |
||overlays/* | Device tree overlays |<https://github.com/raspberrypi/firmware/tree/master/boot/overlays> |

## Getting seL4 onto your Raspberry Pi 4

Because you have applied a device tree overlay to use the UART on GPIO pins 14 and 15,
you will have to update seL4 to use serial0 instead of serial1.
In the kernel at `src/plat/bcm2711/overlay-rpi4.dts`, you should replace all instances of
`serial1` with `serial0`.
The final step to test that you have setup your RPi4 correctly is to build and run the
seL4test project.

Then, you should then build the kernel, such as in seL4test:
You will see that the `init-build.sh` command contains the flag
`-DRPI4_MEMORY`, this specifies how much RAM exists on the Raspberry Pi that will run
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the final seL4 image. Since seL4 needs to know the physical memory layout of the hardware
at build time, and the RPi4 has multiple models with different amounts of RAM, we have to
specify how much RAM the system will have when we build seL4. If `-DRPI4_MEMORY` is not supplied,
seL4 defaults to expecting 8GB of memory.

{% include sel4test.md %}

The boot method described here is through the SD card. You should set up the files
on your SD card as described in the previous section.
Now that we have a bootable image, we can run it on your RPi4. The following instructions describe
how to use a microSD card to boot seL4, using the seL4test image as well as the files mentioned
in the previous section.

The first step is to copy the seL4 image onto the microSD card to the root directory. After
removing the card from your computer and inserting into your RPi4, you can power on the RPi4.

Once the RPi4 boots up, you will see something like the following text from U-Boot:
```
Hit any key to stop autoboot: 2
```

At this point you want to interrupt the U-Boot booting process by pressing any key.

You will now be in the U-Boot command prompt, type the following command:
```
fatls mmc 0
```

Following this, copy your seL4 image (such as an seL4test image) onto
the SD card in its root directory. You can now remove the SD
card from your PC and re-insert it into the RPi4, and power the RPi4 on.
You should see the seL4test image you just placed on your microSD card.

When the RPi4 boots up, be sure to interrupt the boot process and drop
into the U-boot command prompt. From the U-boot command prompt, type
something like the following: `fatls mmc 0`. If you don't see your seL4 image
filename printed out, then you might need to double-check your steps
so far to make sure you didn't forget something along the way. If you
see your file listed, then do something like:
From here, you can load and boot the image using:
```
fatload mmc 0 0x10000000 sel4test-driver-image-arm-bcm2711
go 0x10000000
Expand Down