Behind the new PICMG box PC standard
A new standard is being proposed by the PICMG group for box PCs. Nick Flaherty talks to Mathias Beer, Chief Product Officer (CPO) at Ci4Rail GmbH in Nürnberg about the details of the new standard
“The standards in the market offer modularity and scalability but in most cases come with expensive eco-system around them, CompactPCI for example needs a backplane and management boards,” said Beer. “The market has moved more to the box PC, which can do the same things as CPCI or VPX but with less modularity and no standards. So customers who chose a box PC have to stick with that supplier, and even in a supplier there are different box PC versions. So we said lets combine the advantages of a modular system that you can define with the advantages of the cost sensitive box PC world.”
“The standard is designed for all use cases and these are often used for retrofit, for example in trains, so you need to be very flexible in the mounting system. 19in racks are still a very common mounting system in transport and industrial automation. Sometimes there are subracks where the space is not used so the box can be easily added with just two brackets. It’s about using any space you have left.”
The standard defines a box PC that could be 84HP wide across an entire 19in rack but the focus is more on 3 and 4 slot and 6 slot as the more typical sizes, he says. This creates interoperability, remove single source risk and extends the portfolio for various combinations of products for different market and application segments.
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The height and depth of the box is fixed by the IEC 60297-3-100 and IEC 60297-3-101 standards, with width is variable in multiples of 7HP, or 35.36mm. He expects the most common sizes to be 14 HP, 21 HP and 28HP, up to 42HP, or half the width of a 19in rack.
The proposed standard defines three boards for front, rear and processing in a 7HP form factor that can be linked together with a proprietary link, and linked to neighbouring boards using a standardised PCI Express link. This avoids the need for a backplane and allows boards from multiple suppliers in a scalable enclosure that can be in those different widths.
“The standard is a little bit different – it’s not for the customer to configure the system. It allows the manufacturer or system integrator to use different units from different suppliers,” he said.
“Every 7HP unit can consist of up to 3 PCBs – this would be considered to be from one manufacturer and solves the problem of adding four ethernet interfaces for example. How these three PCBs communicate doesn’t matter and the links to the outside world are not defined, but there are quasi standard connectors, such as 8pin X-coded M12 for gigabit ethernet, or D-sub for serial interfaces.”
“The interface connectors are standardised from board to board so that boards from manufactuerrs can be combined. The interface between the I/O and the board is limited to older PCI Express 2 or USB 2.0 as it is stacked. Each board communicates with its neighbour, similar to PC-104,” he said. “PCIe 3 is possible but hasn’t been implemented yet.”
A key advantage is using the casing as the heatsink for passive conduction cooling.
“The processor board can be 7HP, 14HP or 21HP which allows a bigger heat pump or heat spreader. The standard does not expect to use existing boards because the board orientation is 180 degrees,” said Beer. “Of course you can use COM Express boards (also defined by PICMG) but it will define the width as the depth is defined to be as short as possible.”
“The products we have defined so far do use a computer on module approach but this is a proprietary form factor,” he said.
He sees the standard aiming at single core ARM to quad core ARM with neural networking or dual core Intel Atom processors. “We had to find a compromise with performance up to 85 degrees,” he said. “The processor choice depends on the application needs and desired operating temperature.
There are no plans for a rugged version of the standard, he says.
“If you want an IP67 enclosure or military version then it’s more costly so on our roadmap I don’t see a real rugged version as this is counter to the initial intentions we had. During the standards process we had this discussion, but a rugged version changes the whole cost situation.”
The aim is to have the full standard out by the end of the year. “I’m confident the standard can be closed by the end of the year and released,” he said.
www.picmg.org; https://www.ci4rail.com/
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