For the first time in many years, high-end embedded processors are available on two Computer-on-Module form factor options, COM-HPC^® Client and COM Express^® Type 6. The arrival of the 11th Gen Intel^® Core^® processor generation (codenamed Tiger Lake) presents developers with the opportunity to decide which form factor most closely matches their project requirements.

(Caption 1: COM-HPC Client interfaces differ from COM Express Type 6 mainly in the number and bandwidth of PCIe lanes, Ethernet interfaces and USB ports. In addition to its interface differences, COM-HPC Client, unlike COM Express Type 6, has extended remote management support (yet to be specified).)

New questions

COM Express has dominated the high-end embedded computing field. But, now the arrival of COM-HPC is raising new questions for anyone evaluating their next high-end embedded project. One question is whether COM Express and COM-HPC compete with one another. The answer is no, as their specifications are designed to supplement each other, that is why both form factors support 11th Gen Intel Core processors.

Another question, now that both form factors are options, is whether to scale existing COM Express investments or switch to a new module standard with the need to design a new carrier board as well. The scale or switch decision is particularly relevant for developers who have so far relied on COM Express. They may also wonder: Does the beginning of COM-HPC also herald the end of COM Express? How long will COM Express continue to be available? Do I have to switch to COM-HPC now, or can I wait? Another consideration is how a switch to COM-HPC would affect OEMs’ and customers’ competitive positions. To answer these questions, it is important to know what COM-HPC Client modules have to offer and how they differ from COM Express Type 6 modules.

Basic and Size A: Only marginal footprint differences

COM-HPC Client, like COM Express Type 6, is a PICMG Computer-on-Module specification. It is part of the new COM-HPC standard. This also specifies COM-HPC Server modules, but these do not need to be considered further in this paper because they are server-oriented and headless, while COM-HPC Client modules, like COM Express Type 6 modules, support graphics. COM-HPC Client modules come in three footprints of 120 mm x 160 mm (Size C), 120 mm x 120 mm (Size B) and 120 mm x 95 mm (Size A). So, the smallest COM-HPC footprint is almost identical to COM Express Basic at 125 mm x 95 mm. COM Express Compact at 95 mm x 95 mm is around 21% more compact. As the COM-HPC Size A form factor is only 4% smaller than COM Express Basic, changing from COM Express Basic to COM-HPC Size A is therefore no problem with regard to footprint.

The larger Size B and Size C COM-HPC Client modules sizing is such that these modules would typically sit above COM Express Type 6 modules and therefore address high-performance applications that cannot be implemented with COM Express

(Caption 2: COM-HPC Client defines three different footprints, just like COM Express. As the smallest, Size A, is more compact than COM Express Basic, developers can easily switch from COM Express Basic to COM-HPC Size A.)

Developers who use COM Express Basic in order to integrate processors more powerful than those available on COM Express Compact can opt for the COM-HPC Client Size A form factor. However, there is no COM-HPC Client option for the COM Express Compact size layout. This shows clearly that the two specifications are complementary options.

COM-HPC specifies higher TDP

Just as they offer larger footprint options compared to COM Express, COM-HPC modules also generally allow a higher power budget. With up to 200 watts Thermal Design Power (TDP), COM-HPC Client modules can have approximately three times the current performance of the most powerful COM Express Type 6. Compared to COM Express Basic, at its upper limit of 137 watts TDP, COM-HPC Client TDP is 46% higher. For developers needing more TDP and processor power now or in the long term than COM Express allows, COM-HPC is a must.

COM-HPC Size A modules, such as the new 15-watt conga-HPC/cTLU with the 11th Intel Core processor generation, will be more comparable to the performance range of previous COM Express modules. In addition, COM Express designers will find COM-HPC has the advantage of offering massive more data bandwidth than COM Express Type 6, as evident from the number of signal pins.

(Caption 3: The conga-HPC/cTLU COM-HPC Size A module requires a completely new carrier board. The COM-HPC evaluation board is expected to become available in October 2020)

Nearly doubling the pin count increases bandwidth

Two further key differences between COM Express Basic Type 6 and COM-HPC Client Size A are the connector and the number of signal pins connecting the module to the application-specific carrier board. Like COM Express, COM-HPC is based on two connectors, but now each COM HPC connector has 400 pins. The two COM Express connectors have 220 pins each. The expansion to 800 signal pins makes it possible to connect approx. 80% more interfaces.

Designed for the latest high-speed interfaces, the COM-HPC connector is also compatible with the high clock rates of PCIe 5.0 and 25 Gb/s Ethernet. COM Express currently only extends to PCIe Gen 3.0 and PCIe 4.0 in compatibility mode, making the connector a limiting factor. However, there are efforts to replace the COM Express connector with one that is mechanically fully compatible but electronically more powerful and compatible with PCIe 4.0. This connector replacement bodes well for the future of COM Express.

Memory capacity depends on the footprint

Both COM-HPC and COM Express use SO-DIMMs or soldered memory for RAM capacity. As noted earlier, the footprints of COM Express Basic and COM-HPC Client Size A differ only slightly. It’s already been shown by COM Express Basic that RAM capacity currently tops out at 128 Gbytes, so given how close Size A is to COM Express Basic, the RAM capacity for Size A would be similar.

Developers whose designs require more RAM must use larger form factors. Although COM Express does specify larger modules above the Basic form factor, in practice these have been virtually no relevance. The expectation therefore is that larger modules will be developed primarily based on the COM-HPC standard. And this is likely to happen soon because COM-HPC Server modules address solutions up to the mid-performance server class that can never have enough RAM. They can host eight full-fledged SO-DIMM memory modules and thus currently provide up to 1.0 Terabyte of RAM. Comparing the newly launched Tiger Lake UP3 COM Express Type 6 Compact and COM-HPC Client Size A modules, the latter provide more memory. However, this potential of more memory has not been used; both modules offer two SO-DIMM sockets for 3200 MT/s and 32 GB DDR4. So, 64 GB RAM in total. The reason for this unused potential is simple: The Tiger Lake UP3 cannot support more. All other things being equal, a change driven by the need to get more RAM invariably means opting for a larger form factor than COM Express Basic or COM HPC Size A. However, with memory density continuously increasing, RAM capacity is unlikely to become a limiting factor for targeted multi-purpose applications in the future.

Same graphics, new audio

The graphics support is also the same for both standards. COM-HPC Client and COM Express Type 6 both support up to four displays via three digital display interfaces (DDI) and one embedded DisplayPort (eDP). For multimedia interfaces, COM-HPC replaces the HDA interface previously available with COM Express with SoundWire. SoundWire, a new MIPI standard, requires only two lines and operates at rates of up to 12.288 MHz. Up to four audio codecs can be connected in parallel over these two lines, with each codec receiving its own ID to enable evaluation, a plus for applications where sound plays an important role.

(Caption 4: The conga-TC570 COM Express Compact module with Intel Tiger Lake UP3 processor can be plug & play mounted onto existing COM Express carrier boards – regardless of whether they are designed for COM Express Basic or Compact. They are therefore ready for immediate use.)

PCIe and GbE Support

COM Express Type 6 modules have a maximum of 24 PCIe lanes as compared to 49 in COM-HPC Client modules. One COM-HPC Client PCIe lane is reserved for communication with the carrier board’s Board Management Controller (BMC).

The COM-HPC Client module specification also offer direct connection of two 25 GbE KR- and up to two 10 GbE BaseT Ethernet interfaces. COM Express Type 6 supports a maximum of 1x1 GbE, but additional network interfaces can be connected via PCIe and executed via the carrier board. However, this full potential of the specification is not exhausted by today’s’ 11th Intel Core processor generation.

Both modules offer a PCIe x4 Gen 4 interface for extremely high bandwidth connections to peripherals. In addition, developers can also use 8x PCIe Gen 3.0 x1 lanes with both modules. So, there is no processor-related difference in this respect. However, the COM-HPC modules offer 2x 2.5 GbE native connectivity, while COM Express modules only support 1x GbE natively. COM Express designers therefore must bear the expense of obtaining carrier board components to produce the same GbE functionality as that of COM-HPC modules.

Both modules also support Time-Sensitive Networking (TSN) for real-time communication via Ethernet. So, apart from 2.5 GbE being available only with COM-HPC modules, the differences regarding PCIe and GbE are currently not that significant.

High USB bandwidth and native camera support

Designed for the faster new USB standards, COM-HPC Client specifies up to 4x USB 4.0 interfaces, supplemented by 4x USB 2.0. COM Express Type 6 modules, on the other hand, can execute up to 4x USB 3.2 and 8x USB 2.0. With four fewer USB 2.0 ports than COM Express Type 6 modules, COM-HPC Client nevertheless offers greater bandwidth because the USB 4.0 transfer rate is 40 Gbps.

COM-HPC natively supports up to two MIPI-CSI interfaces. In addition to being cost-efficient, the two interfaces make it easy to integrate cameras for many application types and enable 3D vision. Potential use cases for modules with two MIPI-CSI interfaces include user identification, gesture control and augmented reality for maintenance. Additional possibilities are video surveillance and optical quality assurance, situational awareness for autonomous vehicles and collaborative robotics. MIPI-CSI interface support is thus a clear COM-HPC strength. The conga-HPC/cTLU offers these two MIPI-CSI interfaces. What’s more, the conga-HPC/cTLU includes – with the x86 instruction set extended in Tiger Lake UP3 – AI/DL instruction sets, Vector Neural Network Instructions (VNNI) support and features on top up to 96 execution units of the new processor integrated Intel Xe graphics (Gen 12).

COM-HPC further offers 2x SATA interfaces to connect traditional SSDs and HDDs, along with industrial interfaces such as 2x UART and 12x GPIO. 2x I2C, SPI and eSPI complete the feature set. All in all, COM-HPC Client features are comparable to those of COM Express Type 6 modules, although a CAN bus support option is available with the latter.

Experience shows there’s no rush to switch

The similarities and differences for COM-HPC Client and COM Express Type 6 described above indicate that the majority of designs will be well served with COM Express for at least the next 3-5 years to come. Another factor in that prediction is that COM-HPC Client does not introduce a new system bus. This is different compared to previous changes from ISA to PCI and from PCI to PCI Express. Here it was absolutely necessary to define a new pinout. It’s also worth remembering that COM Express modules did not replace ETX modules as the best-selling modules until 2012 – a good 11 years after the introduction of ETX – and seven years after the introduction of COM Express. And ETX modules are still available today. PCIe generations are backwards compatible, enabling PCIe Gen 3.0 designs to live on for a long time, even after PCIe Gen 4.0 is established across all processor levels. There is definitely no need to switch if a design’s interface specifications and bandwidths are sufficient.

Who should opt for COM-HPC?

All those who require one or all of the following interfaces natively supported by the modules, must switch to COM-HPC: full USB 4.0 bandwidth, 2.5 GbE, SoundWire, and MIPI-CSI today. Those who expect to need more or higher-performance PCIe or Ethernet interfaces with up to 25 GbE in the future should also give preference to COM-HPC Besides, developers of high-performance systems may want to consider that it is easier to scale down when using one standard – an argument for implementing everything in COM-HPC. Otherwise, the motto is: “Never change a running system.” Not at least because COM Express can be made available with a brand new, PCIe 4.0 compliant connector.

Remote management for edge server modules is coming

As part of the COM-HPC launch, an extended remote management interface is also planned. This interface is currently being developed in the PICMG Remote Management Subcommittee. The goal is to make a reduced portion of the complex Intelligent Platform Management Interface (IPMI) feature set available for the remote management of edge server modules. With this new feature set, OEMs and users will be able to easily ensure server-grade reliability, availability, maintainability and security (RAMS). A board management controller, to be implemented on the carrier board, makes it possible to expand remote management functionality to individual carrier board and further system demands as needed. This provides OEMs with a consistent basis for remote management, which they can modify according to their requirements.

Conclusion

COM Express has a great future in an existing performance level with a growing digitalisation. COM-HPC (High Performance Computing) can fullfil a broad range of upcoming compute-intensive applications where bandwidthintensive data streams must be processed in a compact edge device. Further information about congatec’s 11th Gen Intel Core processors based embedded computers can be found on the main landing page https://congatec.com/11th-gen-intel-core/