News New Raspberry Pi 3 variant returns to Model A+ design

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Power, size, and weight. Price is a key point, too - it's a third cheaper, give or take - but it's power, size, and weight that are the key. For a robotics project, the Pi Zero is too limited (needs a special adapter to use a camera, only has a crappy single-core 32-bit processor) but the Pi 3B+ is too hefty (big, heaviest Pi on offer, draws nearly 6W under load and north of 2W at idle, and has the useless USB and Ethernet ports you're not even going to use.)

The Pi 3A+ is the answer. Smaller and lighter than the Pi 3B+, loses the bits roboticists and other embedded types don't care about, retains the bits they do care about (Wi-Fi, Bluetooth, full-size CSI), and has the same performance (so long as your workload fits in 512MB, of course.) For anyone working on embedded computer vision, the 3A+ is the Pi for which they've been waiting.

If you're wanting a Pi to run as a desktop, the 3B+ is a better choice - but the 3A+'ll do in a pinch, as you can connect Bluetooth keyboards and mice to keep the USB port free. They're not that expensive: here's a laptop-style arrangement for under £15.

 

There's a reason for that: compatibility. The Pi family is, to my knowledge, absolutely unique in the world of single-board computers for one sole reason: you can take the latest Raspbian operating system, flash it to a microSD card, and run it on absolutely any model. I mean, you'll need a microSD-to-SD adapter to plug it into anything older than the Model B+ and a daughterboard for any of the Compute Modules, but it'll run just fine and dandy.

When I say "any model," I mean any model. The microSD I used for testing the Pi 3A+ can not only be shoved into my pre-production Raspberry Pi Model B sample, but it can also go into any one of the 50 original Alpha boards - boards almost completely unrecognisable as a Raspberry Pi - without the slightest modification and it'll run just fine. Scratch 2 won't work, and that's about the only problem you'll run into.

The reason this works: the fact that they're all based on the BCM283x SoC family. Each revision has bumped up the processor side - BCM2835 was single-core 32-bit 700MHz later bumped to 900MHz, BCM2836 was quad-core 32-bit 900MHz, BCM2837 was quad-core 64-bit 1.2GHz, BCM2837B0 was quad-core 64-bit 1.4GHz - but left the VideoCore-IV alone because that's the entire heart of the design. (Broadcom originally built it for set-top boxes, y'see, hence the powerful-for-the-era GPU and weak CPU of the BCM2835).

That's great for compatibility, but adds a major problem to the mix: you can't upgrade anything except the CPU side. The GPU handles everything from boot onwards; change the GPU, you've not got a BCM283x any more. That's why even after all these years the Pi doesn't have a SATA port, only has one USB lane, is limited to an absolute maximum of 1024MB of RAM, and has the same approaching-seven-year-old GPU.

I've used a lot of words to get to the good news, though: as hinted at in the article, things may be changing in the future. Co-founder Eben Upton told me during our interview a few weeks ago that the Pi 3A+ represents 'tidying up Classic Raspberry Pi' - hinting pretty heavily that the Raspberry Pi 4, which I have to stress doesn't even exist as a design yet and is in the very early "what would we like to see on it" stage, could finally move away from the BCM283x to something with a beefier GPU, more USB lanes, and possibly additional connectivity like SATA - along with, finally, more than 1GB of RAM.

If it does, backwards compatibility will be lost - but it may be a sacrifice worth making, because like you say there are plenty of boards out there happy to take people's money for more RAM, faster processors, and extra connectivity, so the demand is obviously high.

 

Then you want the Pi 3B+, which comes with gigabit Ethernet as standard...

...which tops out at 300Mb/s because it's still sharing a single USB lane to the SoC. Still, it's better than the 80Mb/s of the older models!

 

Aye: that, along with there only being a single lane of it no matter how many physical USB ports it has, is another peculiarity of the BCM283x family. That ain't changing until (or unless) a future PI ditches backwards compatibility and moves to a new SoC family.

 

You haven't done much work in the wonderful world of Arm, have you?

 

<dissolves into hysterical laughter>

 

I'll let pre-reformation Linus Torvalds explain, in his own inimitable way.