Aegis-GPU1.8 Cable types and transceivers
Telling optical from copper modules and reading module details with mlxlink.
Key points
A transceiver converts electrical signals to light for optical cables. DDM (Digital Diagnostic Monitoring) is the transceiver's built-in readings, such as temperature and optical power. mlxlink checks and debugs link status for passive, active and transceiver cables. Its --cable --ddm option reads the DDM data.
What NVIDIA says (2)
“The mlxlink tool is used to check and debug link status and related issues. The tool can be used on different links and cables (passive, active, transceiver and backplane).”
“--ddm Get cable Digital Diagnostic Monitoring information”
A transceiver converts electrical signals to light, or drives a copper link, at each cable end. Optical and copper types use different firmware images. You can tell them apart by vendor part number.
What NVIDIA says (2)
“Note that we can have both optical & copper type transceivers - these can be identified by Vendor PN and running show explicitly.”
“each transceiver type has different firmware image.”
Before trusting a link, confirm the cable or module is the type you planned. mlxlink --show_module prints its identity, such as OSFP, optical or copper, the part number and FW version.
What NVIDIA says (2)
“-m |--show_module Show Module Info”
“Cable Type : Optical Module (separated)”
Key terms
- mlxlink: The NVIDIA tool that checks link state, cable or module details, error counters and the signal eye on a port.
- Transceiver: The module at a cable end that sends and receives the signal; optical and copper types use different firmware.
- Digital Diagnostic Monitoring: Live readings from a cable module, such as temperature and optical power.
Sample question
You suspect a bad optical transceiver on a ConnectX port. Which NVIDIA tool reads the cable's Digital Diagnostic Monitoring data?
Show the answer
Answer: mlxlink with --cable --ddm
A transceiver converts electrical signals to light for optical cables. DDM (Digital Diagnostic Monitoring) is the transceiver's built-in readings, such as temperature and optical power. mlxlink checks and debugs link status for passive, active and transceiver cables. Its --cable --ddm option reads the DDM data.
What NVIDIA says (2)
“The mlxlink tool is used to check and debug link status and related issues. The tool can be used on different links and cables (passive, active, transceiver and backplane).”
“--ddm Get cable Digital Diagnostic Monitoring information”
Practice 1.8 (3 questions) Full System and Server Bring-up guide
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