Selecting CompactPCI Serial for creating modular embedded computing systems

CompactPCI Serial (PICMG CPCI.S-0) has emerged as a next-generation serial architecture capable of the performance of competing technologies at a fraction of the cost.

1As described in the first installment of this article (, the CPCI-S.0 specification has revealed key innovations to extend CompactPCI into the age of high-speed point-to-point serial interconnects. This installment covers the costs and benefits of using CompactPCI Serial versus other serial-based architectures such as VPX/OpenVPX, as well as CompactPCI Serial's viability in modern communications and industrial applications.

First of all, let’s compare CompactPCI Serial and competing bus standards VPX/OpenVPX.

Originally, VPX (ANSI/VITA 46.0-2007 VPX: Base specification) was built around plated MultiGig RT2 connectors from Tyco Electronics with throughput capacity of 6.25 GHz. The specification allowed up to 64 differential pairs for inter-module communication between 3U boards in the system and 192 pairs for 6U. Recently, a new connector with a throughput capacity of 10 GHz (comparable to CompactPCI Serial) has been standardized for the VPX/OpenVPX systems through the ANSI/VITA 60.0-2012 VPX: Alternative Connector for VPX specification. Accordingly, VPX module and system manufacturers have no barrier to increased speed other than migrating to the new connector, as VITA 46 modules and motherboards are incompatible with VITA 60.

Probably the most important difference between CompactPCI Serial and the VPX/OpenVPX standards is the description of pinouts. Namely, the CompactPCI Serial standard expressly defines which signal should be present in each connector pin, while the OpenVPX standard determines this through “profiles,” or pin designations tied to various interconnect topologies that are subdivided into module, slot, and motherboard descriptions. Provided the number of profiles described in the OpenVPX specification, at times this can result in tens or sometimes in hundreds of pinouts in 3U or 6U systems (Table 1). Further, there are more standardized interconnects than in CompactPCI Serial, and their topologies include double star, ring, mesh, and others. The consequences of the OpenVPX pinouts are simple and complex at the same time: inter-modular compatibility is possible only within compatible profiles, which in practice means from one manufacturer. In contrast, CompactPCI Serial allows system design with modules produced by different companies since inter-modular compatibility is guaranteed by the specification.

Table 1: Comparison of CompactPCI Serial and VPX/OpenVPX technologies.

Modular platforms granularity

With reference to modular platforms, granularity describes a parameter that should be set by the system developer. Granularity is an important for developers that plan on releasing a line of products with varying characteristics based on a particular technology. In modular bus systems, granularity is usually represented by one module of the system, which differentiates units of power, volume or cost, number of operations per second, and so on.

3U CompactPCI Serial systems have a low granularity of roughly 30 W and $1,000, while 6U systems average about 70 W and $3,000. Such values of granularity are well suited for creating control and supervisory complexes and measuring equipment, with 3U systems being more suitable for the execution of customer tasks and 6U systems maintaining server-level functionality and designation. Given the same size and computing parameters, VPX/OpenVPX systems are at least twice the cost of a CompactPCI Serial platform, and accordingly have a granularity-to-cost ration that is higher and in some cases may lead to budgetary constraints.

CompactPCI Serial in network infrastructure

The original CompactPCI standard was designed for use in the core of telecommunications networks, but since the end of the 1990’s the 1-2 Gbps switching capacity provided by CompactPCI has been replaced in the network core by 10-40 Gbps ATCA systems and rack mount server solutions. What about CompactPCI Serial?

With updated throughput capacity, CompactPCI Serial can be successfully used in IP-based network infrastructure systems, however new possibilities for the serial standard more likely exist at the network’s edge. Regardless of information type (digital home, digital transport, digital office, or subscriber data), CompactPCI Serial equipment can facilitate network access and recognize different wire and wireless data transfer protocols, then aggregate and convert these data flows in TCP/IP for preprocessing. For example, CompactPCI Serial’s switching capacity allows for task resolution in process or vehicle control networks, and has already been successfully installed in the Wi-Fi systems of European trains.

6U CompactPCI Serial also offers interesting opportunities in the creation of network infrastructure by way of Power over Ethernet (PoE). End devices such as IP surveillance cameras, panel computers, and controllers can be connected to a CPCI Serial via network cable and powered up to 40 W. By way of the P0/J0 connector, 6U CompactPCI Serial modules can also be provided with an additional 48 V power supply via the motherboard with maximum current of 1.9 A (91.2 W).

СompactPCI Serial in industrial applications

The CompactPCI/VME standards have gained strong positions in many niche markets like production automation, complex process equipment and programmable-controlled machines management, control and communications, transport, defense, and many others. The CompactPCI Serial standard allows simplification of the system creation process, as system developers have the option between 4 types of interconnects, significantly reducing the number of bridges for communication between peripheral and the system controller. In addition, CompactPCI Serial offers a direct connection to SATA drives, the use of chipset-integrated RAID, USB ports, CompactFlash, and SD and microSD USB card readers to list just some of the standard’s updated features that preclude the need to bridge microchips and their drivers.

There is also a wide range of possibilities for integrating PCIe-based peripheral modules with CompactPCI Serial, including:

  • Wired or wireless data transfer expansion modules
  • 1х1 PCIe CAN controllers and COM ports
  • 1/10 GbE copper or optical interface controllers
  • Low-level graphics coprocessors
  • High-level coprocessor (graphics/network DSPs or FPGAs) modules based on 1x8 PCIe

It is important to note that CompactPCI Serial’s overall dimensions allow these application modules to be applied as monolithic boards or MiniPCI Express, PCI-E, XMC, and FMC carrier cards, or even PC/104 SBCs.

Real-time and complex systems requiring Fourier conversions will perhaps benefit the most from CompactPCI Serial, as the system controller’s support of PCI Express requires no additional switches, therefore providing low-latency data exchange and high rates of inter-module exchange. This enables clustering the resources of several modules, as modules such as the FASTWEL CPC510 module can leverage a semi-transparent PCIe bridge and be inserted into both the system controller slot and a PCIe peripheral slot. This creates a quad-core coprocessor with each core capable of executing up to 8 instructions with floating point precision in a single cycle.

The CompactPCI Serial connection

Just as everything in this world, universally recognized embedded specification lifecycles are limited: they have a development stage, a proliferation stage, and then gradually fade. The embedded hardware lifecycle is also closely connected to the synchronization of module availability with current market demand. Considering these two factors, the life expectancy of a well-executed embedded hardware specification ranges from 15 to 25 years, and will shrink as technology development continues to accelerate.

CompactPCI Serial has become the new base specification for modular embedded system design, integrating the dimensions, mechanics, and compatibility of past architectures with the high-speed serial interconnects, interfaces, and driver support of today in an effective and cost-sensitive platform. CompactPCI Serial also supports the inter-module data exchange rates

FASTWEL expects CompactPCI PlusIO (PICMG 2.30) and CompactPCI Serial system controllers and peripheral modules necessary for the evolution to optical interconnects in the near future, allowing system developers to integrate specialized application and coprocessor modules with FPGAs, network processors, radio paths, and the like to this open specification. In other words, development with CompactPCI Serial systems is a path to next-generation system design with minimal barriers.

Alexander Buravlev is Technical Director of Aquarius Ltd. and a Fastwel technical expert.