PICMG publishes a guide for building COM-HPC carrier boards

PICMG has published a COM-HPC carrier board design guide for building carrier boards for COM-HPC modules, including guidance on PCIe Gen 5, USB4, and Ethernet KR and KR4 backplane signaling for ports 10GbE to 100GbE.

When PICMG released the COM-HPC (Computer-On-Modules High Performance Computing) Edge server-on-module standard in early 2020, it included specifications for the development of carrier boards for the modules. Yet, due to the complexity of high-end specifications, as well as the many variations and support for new technologies such as PCIe Gen 5, USB4, and Ethernet connections up to 100 GbE, the standards organization has decided that the developers needed more help. PICMG has just released a 160-page COM-HPC carrier board design guide.

The guide is particularly useful for its detailed discussion of the difficult module to carrier board KR and KR4 Ethernet backplane signaling, says PICMG. “To save pins on COM-HPC modules, the sideband signals for the KR 10G/25G/40G/100G Ethernet interfaces are serialized and then must be deserialized on the carrier board,” the group explains. The design guide provides instructions for handling KR/KR4 in seven diagrams.

COM-HPC specifications (left) and dimensions
(Click on images to enlarge)
Source: Congatec

Also of particular interest are the USB4 sections, as well as PCI Express up to Gen 5, which introduce new concepts compared to earlier USB and PCIe specifications. The guide provides schematics and block diagrams for these interfaces and all other COM-HPC I/O, including SATA, Boot SPI, eSPI, eDP, MIPI-CSI, SoundWire, Asynchronous Serial, I2C/I3C, GPIO, and SMBus .

There are also sections on thermal protection and module type detection and guidance on mechanical considerations. These include heat sink/module attachment, alternate board stack assemblies, and board stiffeners for carrier boards.

Basics of COM-HPC

COM-HPC/Client spec supports TDP processors up to 65W while COM-HPC/Server supports processors up to 125W. While Type 7 supports up to 32 PCIe lanes Gen 3, COM-HPC/Client is up to 49 PCIe Gen 4/5 lanes and COM-HPC/Server is up to 65 Gen 4/5 lanes. Compared to Type 7 support for up to four 10GbE ports, COM-HPC/Client supports two 10GbE ports and two 25GbE KR ports. COM-HPC/Server has only one 10 GbE interface but offers 8 25 GbE connections.

COM-HPC’s dual 400-pin Samtec COM-HPC connectors can handle data rates of up to 4096 Gbps with a data rate density of 2088 Gbps per square inch. Connectors are available with stack heights of 5mm and 10mm.

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Like the Edge Server-focused COM Express Type 7 (COM Express 3.0) specification, the high-end COM-HPC/Server variant is headless (no GUIs). This variant is adopted by Adlink’s COM-HPC Ampere Altra, which based an Arm v8.2-based Ampere Altra. The more integrated COM-HPC/Client specification, which has been seen more frequently on LinuxGizmos, supports up to 4 DDI video interfaces with 4K support, as well as dual MIPI-CSI links.

We saw a variety of 120 x 95mm A-size COM HPC client-based modules, including Congatec’s 12th Gen Alder Lake-H based Conga-HPC/cALP and Tiger Lake-based CPU-180 -U of Eurotech. There are also 120 x 120 mm size B customer form factor modules, such as Adlink’s COM-HPC-cAD. Avnet/MSC’s MSC HCC-CFLS adopts the 160 x 120 mm C format.

More information

The COM-HPC Carrier Board Design Guide is available for free download. More information can be found in PICMG’s announcement, and the document itself is here.