Maximum bandwidth support in PCIE/Lane

Hi,

I have planned to use 2 USB3.0 lanes, 1 SATA lanes and one pcie lane so i choose the config#3 for my project. So i would like to know what will be the maximum bandwidth supported in PCIE/lane?

I found the USB bandwidth details in PARKER TRM but i did not find any bandwidth details for PCIE interface. please help us to finish our design?

Regards,
Vimal.

This is actually a PCIe specification. The TX2 PCI controller supports either gen. 1 or gen. 2 speeds. If the end device can handle rev./gen. 2, then this will be used; if not, the signal will throttle back to rev./gen. 1 speeds. If the signal isn’t good enough for that, then there will be no use of the PCIe end device.

Gen./rev. 1 is 2.5GT/s with 8b/10b encoding. Gen./rev. 2 is 5GT/s with 8b/10b encoding. This means one lane at gen. 1 handles a theoretical max of 2GT/s applied to data, and a gen. 1 lane has a theoretical max of 4GT/s throughput for the data. A “gigatransfer/sec” is basically a bit per sec, so if gen. 1, then divide by 8 for bytes/sec, or 250MB/s for one lane; for gen. 2 one lane is 500MB/s theoretical max. See:
https://en.wikipedia.org/wiki/PCI_Express

Whether or not you’ll actually achieve this depends on part if your components are truly gen. 2 compatible, and this includes signal quality. Failing to exactly match the board layout for PCIe might mean some gen. 2 devices clock back to gen. 1, or a gen. 1 might not even work.

If you need more bandwidth, then you will either need more lanes or hardware capable of later PCIe revisions, e.g., the Xavier. Note that although Xavier supports up to rev. 4 that this requires some very good engineering of traces to prevent falling back to a lower revision.

Hi,

Thanks for confirming the bandwidth details. Yes, I have noticed the PCIe supports Gen2 and would like to confirm if there is any known practical bandwidth limitation in the TX2 side.

thanks,
Vimal

I couldn’t guarantee any answer. Basically you have to set the Jetson to max performance mode, and then it depends on the software talking to the PCIe. There will always be some slowing to below theoretical max, but to know for sure you have to just try it. If it works on a desktop PC, then it might still not work as well on the arm64/aarch64 architecture since there are so many differences (e.g., x86 extensions are not the same as arm64/aarch64, and not all ports from one architecture to another use the new architecture’s equivalent extensions).

If you try on a dev kit carrier board you probably have a good starting idea.