Friday, May 31, 2019

Some Raspberry Pi compatible computers

I noticed this spreadsheet over at r/raspberry_pi reddit. I thought I'd write up some additional notes.

https://docs.google.com/spreadsheets/d/1jWMaK-26EEAKMhmp6SLhjScWW2WKH4eKD-93hjpmm_s/edit#gid=0


Consider the Upboard, an x86 computer in the Raspberry Pi form factor for $99. When you include storage, power supplies, heatsinks, cases, and so on, it's actually pretty competitive. It's not ARM, so many things built for the Raspberry Pi won't necessarily work. But on the other hand, most of the software built for the Raspberry Pi was originally developed for x86 anyway, so sometimes it'll work better.

Consider the quasi-RPi boards that support the same GPIO headers, but in a form factor that's not the same as a RPi. A good example would be the ODroid-N2. These aren't listed in the above spreadsheet, but there's a tone of them. There's only two Nano Pi's listed in the spreadsheet having the same form factor as the RPi, but there's around 20 different actual boards with all sorts of different form factors and capabilities.

Consider the heatsink, which can make a big difference in the performance and stability of the board. You can put a small heatsink on any board, but you really need larger heatsinks and possibly fans. Some boards, like the ODroid-C2, come with a nice large heatsink. Other boards have a custom designed large heatsink you can purchase along with the board for around $10. The Raspberry Pi, of course, has numerous third party heatsinks available. Whether or not there's a nice large heatsink available is an important buying criteria. That spreadsheet should have a column for "Large Heatsink", whether one is "Integrated" or "Available".

Consider power consumption and heat dissipation as a buying criteria. Uniquely among the competing devices, the Raspberry Pi itself uses a CPU fabbed on a 40nm process, whereas most of the competitors use 28nm or even 14nm. That means it consumes more power and produces more heat than any of it's competitors, by a large margin. The Intel Atom CPU mentioned above is actually one of the most power efficient, being fabbed on a 14nm process. Ideally, that spreadsheet would have tow additional columns for power consumption (and hence heat production) at "Idle" and "Load".

You shouldn't really care about CPU speed. But if you are, there basically two classes of speed: in-order and out-of-order. For the same GHz, out-of-order CPUs are roughly twice as fast as in-order. The Cortex A5, A7, and A53 are in-order. The Cortex A17, A72, and A73 (and Intel Atom) are out-of-order. The spreadsheet also lists some NXP i.MX series processors, but those are actually ARM Cortex designs. I don't know which, though.

The spreadsheet lists memory, like LPDDR3 or DDR4, but it's unclear as to speed. There's two things that determine speed, the number of MHz/GHz and the width, typically either 32-bits or 64-bits. By "64-bits" we can mean a single channel that's 64-bits wide, as in the case of the Intel Atom processors, or two channels that are each 32-bits wide, as in the case of some ARM processors. The Raspberry Pi has an incredibly anemic 32-bit 400-MHz memory, whereas some competitors have 64-bit 1600-MHz memory, or roughly 8 times the speed. For CPU-bound tasks, this isn't so important, but a lot of tasks are in fact bound by memory speed.

As for GPUs, most are not OpenCL programmable, but some are. The VideoCore and Mali 4xx (Utgard) GPUs are not programmable. The Mali Txxx (Midgard) are programmable. The "MP2" suffix means two GPU processors, whereas "MP4" means four GPU processors. For a lot of tasks, such as "SDR" (software defined radio), offloading onto GPU simultaneously reduces power consumption (by a lot) while increasing speed (usually 2 to 4 times).

Micro-USB is horrible for a power supply, which is why most of the competing devices either have an option for "barrel" connector or make that required. In other words, don't think to yourself that micro-USB is adequate just because that's the only option on the Raspberry Pi, that barrel connectors are more common among the competitors should convince you that micro-USB isn't adequate. You can actually buy USB cables with barrel connectors cheaply from Amzon.com, so it doesn't make much of a difference. I mention this because I hook mine up to the "multiport chargers" so don't want a separate wall-wart power supply that you normally would need if using the barrel connector -- I want just the USB cable instead.

Likewise, most of the competing devices offer eMMC built-in or as an option. This should convince you that booting micro-SD cards is not adequate. There is no way to turn off the Raspberry Pi without risking corrupting the SD card. It's also a lot faster, sometimes 10x faster. However, I use a $10 USB-to-SATA connector and a $20 SATA drive on my RPi to boot the operating system through the USB port, so it's not like this deficiency can't be gotten around.

The spreadsheet lists which operating systems the device is compatible with. In this, the Raspberry Pi shines, compatible with almost any of them. However, lurking underneath this list is which kernel version the operating systems might use. A good example is the ODroid-C2, which has a newer distribution of Ubuntu 18 userland utilities, but is stuck on the ancient and crusty 3.19 version fo the kernel from February 2015 -- over four years old.

The spreadsheet lists which devices include support for infrared. This is presumably to indicate how well it can be integrated into a home entertainment setup.  However, it should also list which ones support the CEC channel on HDMI. This allows the various devices to control and be controlled from each other. If you want to change the channel with your RPi processing voice commands via microphone, then you want CEC supporter rather than infrared support. The RPi has good CEC support, but I don't know about the other devices.

Conclusion

Because there is so much support for the Raspberry Pi, it's hard not to choose that platform. Things just tend to work. If you are doing maker projects, then get an RPi Model B+.

But it's deficient in almost every way to its competitors, especially with the amount of power/heat it consumes.

For home server needs, I'm using a ROCK64 at the moment. It consumes much less power, has real gigabit Ethernet, costs only $25, and has USB 3.0 for much faster access to SSDs. It doesn't have WiFi, but if it wanted that in a server, I'd probably go with the Pine H54-B.

2 comments:

  1. The odroid c2 will support a more recent kernel if you aren't running a desktop environment. I'm running 4.18.8-odroidc2 on Armbian. Arch Linux images for the c2 also include a recent kernel.

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  2. Thanks for writing up this post. I've added some more columns based on your recommendations.

    I've also added conditional formatting to the CPU and GPU columns to make capabilities more salient.

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