Custom peripheral module design

January 6, 2015 OpenSystems Media

The historically popular custom peripheral module design is making a comeback.

“Custom peripheral board design” is a term you probably haven’t heard in a while – one resigned to the same metaphorical bin as cassette players and other technologies past – so you may be surprised to learn of its reemergence.

Effectively a halfway house between an off-the-shelf embedded solution and one fully bespoke, you may have read the same definition referencing system-on-module (SOM) derived design; the emergence of this apparently sleeker and certainly more compact design strategy was, at one time, a nail in the coffin of custom peripheral board developments.

However, many feel they were mis-sold the true benefits of SOM design, particularly the multi-sourcing capability that it purported to offer – that any X form factor SOM is a drop-in replacement for another, protecting against single-source supply chain commitment and our industry demon, obsolescence.

“Multiplexed connector pins” were the dream of SOM designers themselves, enabling them to individually select from a plethora of available I/O for their CPU module design. Though this also resulted in the mating baseboard developer’s nightmare of desperate attempts to circumvent a single sourcing scenario (which led him to the SOM methodology in the first place!).

It’s not only those who develop with bare boards who are flocking back to peripheral module design; long before single board computers (SBCs) were popularized, early industrial computing applications were satisfied by a desktop PC with the client’s IP and I/O needs satisfied by a custom-built ISA/PCI peripheral module.

Of course this approach also suffered with the increasing compactness of SBCs – the PC/104 format took the embedded world by storm and, unlike the SOM industry, remains committed to compatibility by only driving a peripheral bus down the stack, not selectable I/O.

Off-the-shelf PC/104 (and its PCI and PCIe derivatives) expansion modules suffer from two inherent hurdles. Firstly, it would be more than lucky that your complex I/O requirements happen to be completely satisfied by Company Y’s peripheral module, so you may need more than one. Secondly, due to the comparatively low quantities these are manufactured in, they’ll always be relatively high cost.

Designing a peripheral card containing the exact functionality you require on an SBC format that is truly universally compatible thus gives you back that multi-sourcing capability and represses the need for a sizeable PC/104 stack.

True custom design proponents may be more difficult to convince, though with wave “scalability”, “protection against CPU obsolescence”, and a significantly reduced complexity design vs a CPU module – with fewer layers, little or no high speed circuitry, and the lower costs and design risks associated with both – they may well reconsider.

Going back to those historically using converted desktop PCs, you’ll find companies that are less concerned with compactness – today’s Panel PCs and Industrial PCs users, as those are conveniently supplied with one or more available PCI or PCIe interfaces. Perfect!

Today’s Industrial and Panel PC user of course has I/O needs outside of standard PC interfaces that he must address. This can be achieved externally by a modular approach of industrial I/O converters interfacing via LAN/USB, but this necessitates additional mechanical effort in mounting those peripheral products and as per our earlier PC/104 peripheral example – you’ll more than likely will need a number of them.

For these users it makes perfect sense to revert to the historical practice of peripheral slot card design. Why not design a PCI/e card that contains exactly what you need?

By doing this and using a universal bus format, you’ve literally no restrictions as to what off-the-shelf computing core you interface them to. Creatively utilize this ability to provide a scalable solution, across multiple performance ranges, perhaps even display sizes – or so you’re not held to ransom by any particular manufacturer – and you have true multi-sourcing!

It’s true that peripheral module design fills a smaller gap today than it once did, though its often long-forgotten benefits to reducing design complexity and benefitting from the many advantages of off-the-shelf product, alongside improved longevity, means this methodology is never going to vanish.

Rory Dear, European Editor/Technical Contributor
Previous Article
Encryption 201: Static versus dynamic data

Moving data presents a whole new challenge when it comes to encryption. In Part 1, "Choosing the right encr...

Next Article
Top five reasons why you need Requirements Traceability

If you're designing with FPGAs under DO-254 guidance, these guidelines are a must. Requirements Traceabilit...