Hi everyone 👋
According to NVIDIA’s Jetson Orin website and the preliminary data sheet the PCIe lanes on the Orin Nano are Gen3. However, the High-Speed I/O Cluster section in the Orin Technical Reference Manual states that all PCIe controllers are Gen4. Since this TRM is referenced from all Orin modules on the Jetson Support Resources page I presume the same die with the same PCIe controllers is used across all modules/boards and at best some controllers could be disabled. Could anyone from NVIDIA’s embedded team please confirm if this is a software limitation (perhaps for power reasons)? Or do indeed all PCIe lanes on the Orin Nano support Gen4?
Hi everyone 👋
It is a limitation of the PCIe clock. The nano has a lower power budget, therefore even though the controller is Gen4 capable, the Fmax on the clock won’t support Gen4 speeds.
That makes sense, thanks @alclark. One thing I noticed is that according to Table 7-3 in the Jetson Orin NX/Nano Product Design Guide the modules have 10 UPHY lanes, supporting three USB 3.2 ports (each 10 Gb/s) and seven PCIe lanes (each 1.97 GB/s for Gen4; or 985 MB/s for Gen3).
It’s surprising that the three lanes dedicated to USB support 30 GB/s whereas the other seven PCIe lanes only support 13.79 GB/s (Gen4) or 6.895 GB/s (Gen3) in total. Assuming we connect an NVMe via PCIe x4 and utilize all three USB 3.2 ports, can we actually expect the Orin Nano to handle 3x10 GB/s + 4x985 MB/s = 33.94 GB/s (and the Orin NX to handle 3x10 GB/s + 4x1.97 GB/s = 37.88 GB/s), given the limitation you mentioned?
Please ignore—I realized that I messed up bytes and bits.
@igor_furoa the limitation is for the PCIe clock on the nano, I do not believe it should affect anything else beyond the PCIe speed (Gen3 instead of Gen4)
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