Traveling far? Consider changing buses?

It’s ironic how much coincidence plays a role in our lives. Only last week I was discussing with a number of suppliers the need to move the whole PC/104 ecosystem into the new millennium. Sure, there’s PC/104-Plus, which adds the PCI bus – but that’s so 1990s (there’s also PCI-104, which removes the ISA bus completely). But other embedded standards like CompactPCI, VME, PMC, COM, and AdvancedMC have all adopted or adapted to serial fabrics such as Gigabit Ethernet, Serial RapidIO, or PCI Express. Trouble is, these multi-gigabit LVDS-based interconnects are way overkill for most PC/104 applications in terms of complexity, CPU overhead, heat, and of course, cost.

Here’s the coincidence part. Today I learned about a brand new initiative undertaken by PC/104 supplier Micro/sys called StackableUSB. This open standard initiative uses USB 2.0 to facilitate interboard communication in stackable modules such as PC/104. Company president Susan Wooley told me that while the electrical interconnects used in PC/104 may warrant changing, there’s nothing wrong with the mechanical aspects of PC/104. In fact, some years ago I conducted an analysis for the PC/104 Consortium and identified mechanical ruggedness as the number one attribute of PC/104, followed by the ability to stack modules in a Lego-like fashion. A PC/104 “brick” makes a dandy rugged platform for many harsh environment applications – from military to oil and gas exploration.

Micro/sys’s form factor-independent StackableUSB specification relies on a 40-pin Samtec connector (P/N QSE-014-01-L-D-DP-A or equivalent) to route four USB 2.0 links to up to four stacked modules. Each link is directly connected from the “base card” to each stacked card. A similar type (but not identical) Samtec connector mounts on the bottom of the base card and can facilitate an additional four modules, making a nine-card brick possible. Using additional board-mounted USB 2.0 hubs, up to 76 modules can be ganged together at USB 2.0 speeds (480 Mbps).

The advantages of USB 2.0 are many, and I’ve written about them before in this type of application. Only two wires are required per connection (one pair per stacked module), and USB is so ubiquitous in the consumer market that at the recent Consumer Electronics Show (CES) in Las Vegas, one could find USB coffee cup warmers, USB flashlights, and other dirt-cheap USB appliances. One editor remarked, “Is there anything USB can’t do?” This is the kind of chipset and peripheral technology that’s consistent with the needs of low-cost Small Form Factor (SFF) modules.

And since Micro/sys has made its fortune in PC/104, the company coincidentally introduced the SBC1685, an Intel Pentium III-based SBC with Gigabit Ethernet, four USB 2.0 ports, a CF interface, and of course, StackableUSB I/O. Wooley says StackableUSB allows her company to stay focused on the traditional PC/104 x86 market, while also expanding down into the low end with 8- and 16-bit microcontroller SFFs based upon the Silicon Labs 8051 MCU and up into the 32-bit RISC ARMcore controller market.

The StackableUSB specification is open to all suppliers, though Micro/sys has trademarked the logo and is licensing the IP and settling the terms. So committed is Micro/sys to this new interconnect that the company recently resigned its PC/104 Consortium Board position (but remains an active member). It’s also clear that Micro/sys felt compelled to act outside of the PC/104 Consortium in order to move technology forward. Wooley pointed out that although the company was part of the original “gang of five” who invented the EPIC Express form factor, after 18 months of effort by numerous individuals, it still hasn’t been officially adopted as a PC/104 Consortium spec.

So while PCI Express may be the obvious bus for NextGen PC/104 and other SFF modules, it seems that StackableUSB may be a more useful one. Who knows, it might just be a bus that gets designers where they need to go … faster. I’ll keep an eye on this one – it looks promising.

Chris A. Ciufo