COMPACTPCI CompactPCI Serial specification for modular embedded computer systems By Alexander Buravlev, Fastwel This article reviews the new basic specification of CompactPCI Serial, and explains why it was necessary to develop this specification when two basic specifications already existed in the PICMG consortium (ATCA and MicroTCA) and one in the VITA consortium (VPX/OpenVPX). It highlights the advantages of the differ- Figure 1. Development of ent system architectures for interconnects of intermodular specific tasks. data exchange of the PICMG CompactPCI standards family n Embedded computer systems fall into two creation of integral systems. The question of ity about 1 Gbit/s. This bus fulfilled the function classes according to their internal architecture: the right selection of standards is difficult for of universal interconnect, providing both data monolithic (for example, the automobile com- systems developers mainly due to two reasons. exchange for collaborative computing and data puter or the electronics modules of printers The first is that the standards themselves evolve exchange with peripheral and storage modules. or scanners), and modular, consisting of dif- over time in the technical aspect. This can be In the following 10 years two specifications ferent units or boards (for example, radar data rather difficult to follow: changes must be were issued, each of which added serial inter- processing). The first class are generally made monitored and upgraded versions acquired. connects to the parallel PCI bus: 2 Ethernet by big companies in millions of copies, allowing The second reason is that the standard itself channels were added in PICMG 2.16 and 4x1 to allocate huge engineering resources for their can be very interesting from the technical point PCI-E channels and 2 more Ethernet channels development, and quickly recovering the de- of view but not popular in the market. Thus, it were added in PICMG 2.30. And at last, in velopment cost. With the second class of sys- will be difficult to find the necessary modules 2011 the CompactPCI Serial specification was tems it is far more complicated, since volumes both at the system development stage and, adopted, substantially increasing throughput range from a few units to a maximum of what is worse, at the mass production stage. capacities in all types of interconnects: for data some thousands, and the intended tasks are exchange - PCI-E and Ethernet; for storage sys- often impossible for just one controller or The CompactPCI specifications were supple- tems – SAS/SATA; and for input/output systems processor, while the consolidated resources mented in 2011 by the CompactPCI Serial for general profile peripherals - USB 2.0/3.0. consume tens, if not hundreds of watts. For specification. It was developed to combining electronic modules, it is necessary renew the data exchange intercon- to use the one or the other technology. nects between modules in Com- pctPCI systems, and thereby to en- Most of the world’s modular embedded com- sure the solution of the task of cre- puter systems are developed on the basis of ating modular systems over the open standards, describing mechanical con- next 15 to 20 years. struction, heat sink, electrical connections and very often even logical protocols of communi- The CompactPCI history began in cation between the system modules. Such stan- 1999 (figure 1) when the first basic dards simplify the development of industrial specification was published, com- electronics products, using modules from dif- bining the Euromechanics standard ferent vendors without losing the novelty and (IEC 60297) with the PCI bus. At maintainability of the solution itself. The tech- that time the data exchange between Figure 2. External view of the FCI CompactPCI Serial nology of standards lies in ensuring compati- modules was provided by the 32- AirMax VS connectors installed on motherboards (on the left) and blade modules (on the right) bility of modules from different vendors for bit PCI bus with throughput capac- 25 September 2012 COMPACTPCI CompactPCI Serial at first looks to be a logical system controller (Syst) as a host, while Ether- continuation of the tendency of step-by-step net has a full mesh topology or, in other words, transition from parallel buses to serial inter- “each-to-each” topology (figure 3). It is impor- connects of point-to-point type, but if you tant to note that the CompactPCI Serial stan- look at it more deeply and familiarize yourself dard does not impose restrictions on the con- with details, you will see that the CompactPCI figuration of motherboards, leaving this deci- Serial specification represents the new basic sion up to the customer and motherboard specification of the standard family, and this manufacturer. Respectively, some systems can is very important for the industry and devel- be designed for connection of only one appli- opers of embedded systems. cation or peripheral (Per.) module, the others - for connection of up to 24 application mod- CompactPCI Serial has five key innovations: ules. CompactPCI Serial for 6U modules de- new connectors, high speed interconnects, new scribes an additional connector on the system layout of connectors on 6U boards, a new controller module, providing two additional power supply scheme and conductive cooling Ethernet channels which can be used for en- technology. Connectors: CompactPCI Serial suring compatibility with PICMG 2.16, and uses new high-density connectors for data an additional power supply. transfer both on the side of blade modules and on the side of motherboards (figure 2). The mechanical structure underwent few Testing of connectors, for example, FCI AirMax changes but resulted in significant consequences connectors, showed high quality of signals for the 6U systems. Thus, all connectors for transmission up to 12.5 GHz. connection to the motherboard are now located in the upper half of the 6U plate, while the Connectors structure allows installation from lower half remains free and can be used for in- different sides of the board, allowing thereby stallation of connectors according to customer to apply the mezzanine concept of blade mod- specifications and/or for direct connection to ules creation with connection of mezzanines a rear I/O module (figure 4). If the organization directly to motherboards. Interconnects: Com- of the 6U system does not require support of pactPCI Serial outlines expressly the four types PICMG 2.16 and additional power supply, 3U of interconnects pins (pinout) designation motherboards can be used in such systems. and one I2C check bus on the system con- trollers and peripheral connectors: 8 PCI-E Figure 5 illustrates different options for the channels, two of which are 8 and the remaining implementation of CompactPCI Serial systems six are 4; eight Ethernet Base-T channels; (a, b, c) and hybrid systems (d) with monolithic eight SAS/SATA channels; eight USB 2.0 or (a, c) and composite (b, d) motherboards. Ad- USB 3.0 channels; I2C bus for control and vantages consist in the reduction of prices for monitoring of system service parameters. At motherboards - they now became smaller and the physical level each channel consists of two simpler to manufacture, as well as the possibil- differential pairs, providing data transfer from ity of supporting inherited (i.e. inherited from source to receiver and reverse. As all Compact- previous specifications) interconnects (Ethernet PCI Serial interconnects are serial, the specifi- and PCI), and the creation of hybrid systems. cation describes their topology, namely: PCI- In addition to the improvements already men- E, SATA and USB have star topology with the tioned, there is one special mechanical element Figure 3. Intermodular interconnects topologies in the CompactPCI Serial specification: a) PCI-E, SATA and USB; b) Ethernet September 2012 26 COMPACTPCI Figure 4. Examples of connection of front and rear I/O cards to CompactPCI Serial motherboards for the 6U (a) and 3U (b) systems in 3U modules and two mechanical elements vision of power supply to modules with con- in 6U modules, directing and centering the ductive or liquid cooling. CompactPCI Serial boards when connecting to the motherboard provides the system controller with the possi- to simplify the processes of systems assembling bility to control the power supply, for example, and modules replacement for repair. upon occurrence of events (wake on LAN or wake on modem). Therefore, the functions im- New connectors also allowed improving the plemented in all modern processors and chipsets power supply system. Specifically, CompactPCI can be used for creating an embedded system. Serial requires only one supply voltage (+12V) The CompactPCI Serial specification offers with maximum input power of 79.8W for each developers a simple option for implementation 3U module and 171W for each 6U module, of systems with conductive cooling. This option needed for provision of power supply to 8HP assumes packing of the standard board in a or 12HP high-productive modules, or for pro- metal holder which is inserted into the system with the 5HP step between modules. Very often the success of new technical solutions is based on the support of legacy technologies. A good example is the success of the x86 processor architecture, supporting operation of the previously written program code. In the family of CompactPCI specifications, the new CompactPCI Serial specification provides systems developers with very wide possibilities of integration of inherited PICMG 2.0, 2.30 and 2.16 modules within one system. The CompactPCI 2.30 (PICMG 2.30) peripheral and application modules use identical connec- tors and are completely compatible to Com- pactPCI Serial. The system controllers and peripheral 3U mod- ules can be used in 6U systems. More Infor- mation on the compatibility of standard mod- ules of the CompactPCI specifications family is provided in table 1. The CompactPCI Serial specification allows to implement hybrid sys- tems in which the peripherals are based both on serial interconnects and on the inherited 32 or 64-bit PCI buses.