EOMA68 Computing Devices

An Earth-friendly way to easily upgrade and fix your own computer

Sep 19, 2016

Project update 36 of 75

Chips, Prototyping, and Being a Good Houseguest

by Luke Kenneth Casson Leighton

We’re staying with a friend in Hong Kong as we oversee progress on the laptop’s PCBs. The revised EOMA68-A20 was submitted for prototyping and may actually be ready within under ten days. Enquiries are still outstanding for tracking down a S5P6818 Reference Design.

The Limitations of Being a Welcome Guest

Our friend is great; she’s moved to her sofa (which she claims is very comfortable) so we can use the bedrooms in her small apartment. She works extremely hard: out at 8 a.m. and back around 9 p.m. every day. However, it would not be a good idea to ask if we could set up an electronics and 3D printing workshop in her tidy living room. Her study is off-limits too, since it is only 2.5 x 2.5 metres and completely full of desks, wardrobes, cats, and bookshelves.

So, redesigning PCB2 for the 15.6” laptop housing to accept the new Frida LCD requires a small gamble. Specifically, I have to trust the 3D CAD model a bit more than I would like. However, there are some advantages to using Frida’s (lower-cost) LCD: the dog-leg in the PCB which was required for the previous LCD isn’t needed now, so the entire PCB2 can sit flush with the floor of the casework. This means many of other design compromises can also go.

As mentioned in the last update, work on PCB1 is complete. However, unlike the Micro-Desktop (which was submitted for prototyping immediately), because the laptop’s PCBs are heavily interdependent, it’s prudent to hold off on prototyping until all three are properly reviewed. Unlike PCB1 and PCB2, which required only minor adjustment, PCB3 (the power board) is going to need a complete overhaul. Fortunately, it’s only around 25 components.

EOMA68-A20 submitted for prototyping

Mike kindly agreed to get the EOMA68-A20 Card through to PCB prototyping and assembly last Sunday, so it stands a good chance of being completed before the upcoming major Chinese national holiday. I’m not a big fan of doing DDR3 layout adjustments so it’s a bit of a calculated risk, but an extra address line absolutely has to be added. If there were plenty of available budget, I would hand over the EOMA68-A20 PCB designs to a third party, but that would cost around $2,000, nearly the same as producing a set of five prototypes! With those kinds of sums involved, it’s a calculated risk to do the work myself and try it out.

The S5P6818 Chip

The S5P6818 is an eight-core, 28 nm process chip designed by Nexell and manufactured by Samsung. It’s on the candidate list for exploration, over and above that of the Allwinner A64. That’s because the A64 is a quad-core 40 nm process chip. Jumping to 28 nm saves power by a factor of two, while doubling the number of cores. So for the same amount of total power, we can double the number of Cortex A53 cores. Both processors max out at 2GB of RAM (due to hardware address limitations). Since the Nexell processor has been fully documented by FriendlyARM on their wiki, and despite its kernel being only 32-bit and based on Linux 3.4 it’s still a much better choice, libre-wise, than the Allwinner A64. Especially given that Allwinner’s A64 team continue to insist they have a right to violate the GPL to gain some sort of "commercial advantage". All of Allwinner’s 8-core processors use PowerVR (which results in them automatically being blacklisted), so we’re left with the S5P6818 as the currently preferred high-end option.

Last week I telephoned Nexell and they put me in touch with a China-approved distributor. We’re at the "exchange contact details" stage (and have been for over a week). The fact that I’m on the move constantly and so genuinely not able to give a telephone number maaay not have helped. I’ve since bought a dual-sim phone and a PAYG HK sim; next on the list will be a China SIM card. The next step will be to request a meeting in Shenzen next month. If I get no response I’ll go back to Nexell and ask if there’s an alternative distributor (and if they themselves have a Reference Design).

This one example illustrates why it takes such a long time to get new, innovative electronics designs out the door. "Normal" people just use off-the-shelf PCBs or license designs from ODMs. We’re so lucky to have TI and Freescale providing full Reference Designs in the form of the Sabre Lite CAD and Beagleboard CAD files, it’s hard to understand why it’s so challenging just to get hold of a processor from another manufacturer. In the meantime, we’re reaching out to multiple ODMs to see if they’d like, say, $10,000 in exchange for a copy of their S5P6818 PCB design files…

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