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bricks/ev3: Add instructions to build for bare metal.
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‎bricks/ev3/README.md‎

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# Pybricks on EV3 without Linux (Work in progress)
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This Pybricks port is intended to run on EV3 as a "bare metal" port, _without_
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an underlying operating system such as `ev3dev` or `TOPPERS/EV3RT`.
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The goal is to make it very similar to the other "bare metal" ports such as the
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ones we have for the SPIKE Prime Hub, Technic Hub, City Hub, and the BOOST Move
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Hub. By making it work the same, it will become part of the same family of
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hubs. It will be able to use the same online code editor, so that EV3 can be
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used well into the future, even when the official apps are all discontinued.
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This should resolve many open requests to continue support for EV3 in Pybricks
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3.X. It should also resolve technical issues related to device detection and
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[loop time issues](https://github.com/pybricks/support/issues/1035).
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Since it won't have Linux, it won't have certain features like Wi-Fi or support
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for advanced accessories. For those uses cases, Pybricks 2.0 on ev3dev will
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remain available.
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## Requirements
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Since USB communication is not yet implemented, you need the following hardware
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to use this:
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- A USB serial adapter to connect to sensor port 1 on the EV3 brick. You could
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use [this one](http://www.mindsensors.com/ev3-and-nxt/40-console-adapter-for-ev3).
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Or make your own using a standard USB to serial adapter and connecting it to the
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data wires of an EV3 cable.
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- A microSD card (32 GB or less) to store the firmware image.
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## Prerequisites
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Before attempting to build this, please follow the instructions to build the
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firmware for one of the other targets, such as the SPIKE Prime Hub, as
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explained [here](../../CONTRIBUTING.md).
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Then, install the following additional tools:
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```
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sudo apt install u-boot-tools
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```
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Prepare a microSD card (32 GB or less) and format it as a single FAT32
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partition. It is not necessary needed to set any boot flags.
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In the following examples, we assume that the formatted volume is called
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`ev3`.
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## Building the firmware
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```bash
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# Navigate to the repository.
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cd pybricks-micropython
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# Build the uImage.
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make -C bricks/ev3 clean
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make -C bricks/ev3 uImage -j
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# Copy the result and resources to the root of microSD card, e.g:
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cp bricks/ev3/build/uImage /media/user_name/ev3/uImage
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```
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Note: This should not be confused with other existing or outdated EV3 builds in the `bricks` folder such as the `ev3dev` or `ev3rt` builds. They can serve as inspiration, but are completely separate from this build. From a code point of view, this new `bricks/ev3` build will be a lot more like `bricks/primehub`.
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## Operating the brick
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- Connect your serial adapter to sensor port 1 on the EV3 brick.
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- Start a terminal emulator such as `screen` or `picocom`.
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- Insert the microSD card into the EV3 brick.
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- Press the center button to boot.
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You should see something like the following output:
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```
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EV3 initialization passed!
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Booting EV3 EEprom Boot Loader
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EEprom Version: 0.60
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EV3 Flashtype: N25Q128A13B
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EV3 Booting system
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Jumping to entry point at: 0xC1080000
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U-Boot 2009.11 (Oct 26 2012 - 10:30:38)
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I2C: ready
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DRAM: 64 MB
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MMC: davinci: 0
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In: serial
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Out: serial
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Err: serial
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ARM Clock : 300000000 Hz
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DDR Clock : 132000000 Hz
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Invalid MAC address read.
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Hit 'l' to stop autoboot: 0
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reading boot.scr
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** Unable to read "boot.scr" from mmc 0:1 **
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reading uImage
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209016 bytes read
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## Booting kernel from Legacy Image at c0007fc0 ...
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Image Name:
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Image Type: ARM Linux Kernel Image (uncompressed)
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Data Size: 208952 Bytes = 204.1 kB
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Load Address: c0008000
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Entry Point: c0008000
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Loading Kernel Image ... OK
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OK
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Starting kernel ...
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Hello!
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World!
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Traceback (most recent call last):
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File "%q", line %dhello.py", line %d8D��D�, in %q
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<module>
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KeyboardInterrupt:
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Pybricks MicroPython v1.20.0-23-g6c633a8dd on 2024-06-08; MINDSTORMS EV3 Brick with TI Sitara AM1808
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Type "help()" for more information.
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>>>
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```
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You can remove the microSD card after booting. After updating the uImage, you
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can try out your new build by rebooting: Press and hold the center and back
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buttons for 4 seconds.
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For now, there is just the REPL and several builtin MicroPython modules.
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Sensors and motors are not yet enabled.
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## Development status
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This is a highly experimental development. Pretty much nothing is enabled yet.
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The intention is to prepare a minimal build where we can add drivers one by
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one, with help from experts in the community.
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Inspiration for future hardware implementation:
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- [ev3dev](https://www.ev3dev.org/docs/kernel-hackers-notebook/ev3dev-linux-kernel/): Well documented resources for EV3 on debian Linux.
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- [EV3RT](https://github.com/pybricks/ev3rt-lib): RTOS (not Linux). Closer to the metal, but drivers mixed in with RTOS.
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- [am18xlib](https://github.com/pybricks/am18x-lib-ev3): Good inspiration for minimal peripheral drivers, including PRU and so on.

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