SBC recommendation for learning

I am an embedded developer that mostly works with MCUs. As I want to expand my skill set I want to learn about embedded Linux and thought about buying a development board. As I am not too deep in this topic I would like to ask you for any recommendations on a good development board.

My requirements for the board are in general the following:

-Support for the Preempt-RT-Patch.
-Wireless capability (Wifi or BLE)
-I2C/SPI/UART peripherals
-Open-source HW/SW
-Active support (forums/email/community,etc)
-DAC/ADC would be nice but not a must.
-Examples with Yocto would also be nice as I also plan to learn Yocto in the long run.

The requirements are just some guidelines for what I am looking for but I am open to any recommendations based on your experience.

You've probably already seen both the Arduino and the Raspberry Pi Pico. They come in a lot of variants with WiFi and/or BLE. They also support I2C/SPI/UART. Both have community forums.

I've played a little with the Arduino so far, but just in a hobby capacity. There is a lot you can do quickly and easily with it, depending on which model you have, but for somethings it can quickly require more knowledge and experience than a hobbyist will have. It's got its own IDE which is convenient in some ways, but with a little note taking or scripting you can use any other editor instead.

Likely the Raspberry Pi SBCs would be a good option, lots of commercial outfits appear to use various of their boards, for lots of different things.

I use their boards as 'cheap' computers for daily desktop tasks, others program robots & the like - I think they would be worth your time looking into.

https://www.raspberrypi.org/about/

I've worked with Hummingboards, Pi's, and Beagles, never used Arduino, but they're pretty common.

I'd get several, because they're cheap and you can try several flavors of their home grown capabilities.

Personal opinion? Yocto is fine, good distro. I feel it's not very common and if you end up providing an environment for others to build up within, sometimes it's limited for packages, or it used to be for me. I ended up using flavors of Debian or Ubuntu and was very successful. Similarly I've also used buildroot for some embedded targets.

High speed serial (I2C/SPI/UART/I2S/485/Modbus are all available nearly everywhere. Same for different types of networking, wired and wireless, plus the stacks. Many support analog I/O and plenty of examples for things like HD audio, especially on the Pi. The only open source HW ... I believe, is the Beagle, they used to provide their Gerbers and schematics. The Pi seemed ideal at the time, but when we looked at it they did a special sandwich of the flash or RAM under the ARM in a stacked module, so it was very specialized and we didn't think it would be easy for us to send to any general assembly house and duplicate. I don't know if they still do that o their newer models.

A consideration for selecting a board that is rarely mentioned is the SoC documentation.
The SoCs used on the popular Linux-capable SBCs (e.g. Broadcom and Allwinner) typically have rather thin datasheets and technical documentation, maybe not even a hundred pages.
Compare that to what is available for a TI, NXP/Freescale, Microchip/Atmel, or even Marvell SoC.

Assuming that you intend to learn much more than how to install prebuilt Linux distributions, then isn't it necessary to have a full description of every bit of every register of every peripheral integrated in that SoC (without signing an NDA)?
Maybe you'll also find a section on the theory of operation and/or programming guidelines for a peripheral.

Another one to consider might be the ESP32. I've only read a little about it and was considering it for a home project. However, it does have its own forum (and community) and supports I²C, SPI, UART, and others. As far as I know it is open hardware, since there are a lot of different vendors with local models and variations on a theme. Some of those models support WiFi and/or Bluetooth.

One question however is about your plans. The Raspberry Pi models are all general purpose computers, except for the Raspberry Pi Pico. I consider embedded systems more in the microcontroller category. So are you looking for a really low energy microcontroller style of device or more a somewhat low power general purpose computer?

My 2 cents ...

The only SBCs with which I've had personal experience are the Hardkernel Odroid line (C2 and N2+ in my case). Chose them at the time because of their on-board HEVC decoding (pretty sure all the others have caught up ...) and their support for my favourite linux OS, Arch (its Arch Linux ARM variant).

I use one as an off-site backup "server" for a 6TB backup USB HD (the C2 - running Arch ARM) and the other at another site as a media streaming device, running CoreELEC.

I am no developer, so cannot comment on the Odroid line in that respect. In general, they seem to be considered as close cousins of the Raspberry Pi.

Cheers !

Rick

If you are looking for 'active' forum for support network the Raspberry Pi has great support bar none. Very active community and good documentation. However, your first requirement may be a problem. The PI OS out of the box doesn't support the 'Preempt-RT-Patch', But you can surely find out if it can. A lot of what I do doesn't require the real-time as the basic timing is good enough. If I need dedicated response, I would drop to the Pico to get that as there is no 'OS' so to speak. Between the Pico, RPI-4, and the Zeros, you have lots of options for learning. My two cents.