The Specifications Corner: Processor PMC (PPMC) - OpenSystems ...

The Specifications Corner:Processor PMC (PPMC):Taking mezzanines to new heightsBy Jeff DurstFor several years, board-level manufacturers have designed andproduced proprietary mezzanine cards with built-in processors.The inspiration for this hardware sprung from the fact that mostelements on a carrier card, like I/O and serial ports, are static.The central processing unit (CPU), however, is always in fluxdue to ever-increasing clock speeds and functionality. By movingthe processing component to the mezzanine level, users have acomplete processor/memory subsystem that is flexible and easyto upgrade. Baseboards do not have to be swapped each time aprocessor enhancement is made. The cost and resource savingsare obvious.Developing the Processor PMC (PPMC)As bus speeds and semiconductor integration accelerated andcompanies continued to launch advanced processor and memorytechnologies, the focus shifted to building a processor mezzaninecard based on a standard form factor. This has resulted in a newdraft standard known as the Processor PMC (PPMC). DesignatedVITA32-199x, the PPMC draft standard is an extension to thepopular PCI Mezzanine Card (PMC) draft standard, IEEEP1386.1, and delivers processing functionality in a smaller, standardizedform factor.Conceived in early 1999, this new proposal maintains electrical,mechanical, and environmental compatibility with existingPMCs. Although its predecessor is typically seen as an expansionor I/O card solution, the PPMC is a subsystem that includes a presentsignal and can handle interrupts, 66 MHz PCI operation, andPCI bus enumeration. The draft standard also allows the additionof an optional second PCI agent.Redefining previously reserved or obsolete PMC pins implementsthe features of the PPMC standard. Additionally, the standarddeviates from the PMC standard by relaxing side-two heightrestrictions. The boundaries are extended to accommodate largedevices like heat sink- and fan sink-cooled processors, SODIMMsocketedmemory modules, connectors, and power supplies.What does PPMC offer?Standards and details aside, a PPMC module delivers the samebenefits as its proprietary counterpart. Users have the ability toquickly upgrade systems to new processor and memory architectureswhile retaining the carrier board. But unlike vendorexclusiveprocessor mezzanines, the PPMC is an open, modularsolution. That means companies can access the PPMC solutionwithout committing new manpower and manufacturing resourcesto build an application-specific mezzanine. Nor do designers needto buy more expensive custom designs. Because PPMCs can bepurchased off-the-shelf, users are able to speed time-to-marketconsiderably.The benefits are best explained, however, through an applicationexample. A communications equipment manufacturer is buildinga system with a proprietary form factor. Due to its size, theCompactPCI Systems / July-August 2000slot will not fit either a VME or a CompactPCI board. In lieu ofdeveloping a CPU/memory subsystem and dealing with the timeconsumingdebugging process, the user purchases an off-the-shelfPPMC. As a result, the custom baseboard that is fabricated for themachine only has to provide PPMC connectivity. The PPMC handlesthe data and protocol processing, and the system is ready forsale months ahead of schedule.Monarch vs. Non-monarchIn addition to greater flexibility, the PPMC draft standard has alsointroduced two new terms, Monarch and Non-monarch, whichclassify the operational mode of a module. While the modes sharesimilarities with PCI host functionality, it is important to note thatPPMCs do not provide PCI clock, reset, or arbitration functions,and thus the need for an alternate lexicon.A Monarch module is defined as a PPMC that acts as the mainprocessing element. In this mode, the PPMC performs PCI busenumeration at power-up, and handles interrupts from devicesrequesting service. This is the role the PPMC plays in the previousapplication example.Non-monarchs, asSystem Slot Solutionthe name implies,have a contrary function.A Non-monarchPPMC is a secondaryCPU, does not enumeratethe PCI bus,and is an interrupter.In addition, whilethere is just oneMonarch per system,the number of Nonmonarchsis limitedFigure 1 only to the electricalinterface capacity onthe carrier card. Thisallows a variety of subsystems to handle the processing requirementsand to report to the principal CPU as shown in Figures 1 and 2.For instance, a telecomcompany thatruns an SS7 applicationmay use PPMCsin tandem with T1/E1 interfaces. In thisscenario, the I/O processorswould runthe data-link layer(MPT1 and MPT2)of the SS7 stack, anda PPMC would overseethe I/O moduleshandling the higherlevels (MPT3 and up).Peripheral Slot SolutionFigure 2Copyright 2000 / All rights reserved

A second PPMC would take care of the operations, administration,and maintenance (OA&M) functions. All of the distributed processorswould report to the principal CPU.The main reason to design a system with multiple processors isto avoid running all software on one CPU, an architecture thatyields finite performance levels and leaves no latitude or longitudefor improvement. Moving satellite tasks (e.g., OA&M) toautonomous subsystems, in contrast, increases the system’s overallprocessing capacity. Simply put, a hierarchical structure usingMonarch and Non-monarch PPMCs assures that the system canmeet its operational goals and reduce time-to-market.The MONARCH signal designates each PPMC in a system asMonarch or Non-monarch. An optional EREADY signal is alsopossible. This cue, generated by Non-monarch PPMCs, indicatesthat the module has completed its onboard initialization, and canrespond to the monarch’s PCI bus enumeration via configurationcycles.PPMC in the real worldArtesyn Communication Products has emerged as one of severalpioneers in the PPMC market that includes real-time applicationssuch as gateways, switching, call processing, and wireless communications.Released in early 2000, the Artesyn PM/PPC-750,shown in Figure 3, is a working example of the PPMC standard.The PM/PPC-750 combines the speed and computing power ofthe PowerPC750 microprocessor with a variety of connectivityand expansion options that create a highly functional and flexiblesolution. The module retains the original IEEE P1386 PMC envelopein both form factor and power dissipation. Therefore,CompactPCI, VME, or proprietary environments can use thePM/PPC-750 module.A major teledatacom customer employs the PM/PPC-750 moduleas an embedded VxWorks development environment. Engineersplace the PM/PPC-750 on a PMC carrier for PCI, install it into aWindows NT workstation, connect the console serial cable to thePC’s COM port, and drop in a separate Ethernet connection forthe PM/PPC-750. The company sidesteps the cost of a chassis anda full-blown CompactPCI or VME board.Figure 3Another customer has a dual-rail Gigabit Ethernet backplane aspart of a High-Availability system. The company wanted toupgrade this platform for use in another application. To do so,engineers had to build a new node on the Ethernet backplane.Rather than start the design from scratch, designers focused on theoverall application. They included a PPMC site on the carriercard, and inserted the PM/PPC-750 as the main processor. Withthe processor and memory supplied in an off-the-shelf module,the company saved time and money.In other applications, the PM/PPC-750 is used to run upper-layerprotocol stacks or process data coming from a port on the PMCcarrier. The wide range of application examples of the PM/PPC-750 testifies to the flexibility of PPMCs.The Future of PPMCProducts like the PM/PPC-750 are just the beginning of thePPMC invasion. Soon, the PPMC will gain industry acceptanceon par with its predecessor, the PMC. As the draft standardevolves and more PPMC modules hit the market, users will realizethe widespread benefits of processor mezzanines, awarenesssure to fuel a trend toward more distributed systems.Jeff Durst has been with Artesyn Communication Productsfor more than 13 years. He was originally hired as a hardwareengineer and later promoted to project manager. In the engineerposition, Jeff designed single-board computers used in military,scientific, and communications applications. As a projectmanager, he supervised multiple projects for several of today’smajor telecom companies. Jeff recently made the transition toproduct management and is currently focusing his efforts onproduct definition.For more information about Artesyn products, contact Aaron Parker at Padilla Speer Beardsley Inc. at612-872-3759 or email: aparker@psbpr.com.CompactPCI Systems / July-August 2000Copyright 2000 / All rights reserved