Radxa Rock5 RK3588 SBC: PCIe lanes clarification

Hi Radxa & community,

I am trying to read up on the documentation of the Rock5 e.g. from this document Introduce ROCK 5 Model B - ARM Desktop level SBC - ROCK 5 - Radxa Forum and Rock5/hardware/5b - Radxa Wiki, to understand where the RK3588’s PCIe lanes go.

  • On the bottom of the SBC is a M.2 M key 22x80mm slot. A NVMe SSD any other fitting PCIe peripheral would fit here. How many PCIe lanes does it get?

  • On the top of the SBC is a M.2 E key, that one is 22x42mm is it? How many PCIe lanes does it get?

  • Finally do any more PCIe lanes go to any other chips on the SBC?

I would hope it’s 2x lanes to the lower M.2 + 2x lanes to the upper M.2. If I understood it right, the USB3 controller is built-in in the SoC so the USB3 consumes no PCIe lanes.

Looking forward to your confirmation. Thanks!

Oh wait, I see on the RK3588 CPU specs that the RK3588 actually has FIVE PCIe lanes: 4x PCIe v3 + 1x PCIe v2.

Somehow that 1x PCIe v2 is integrated with the USB 3.0 and the SATA, they call it “Combo PIPE PHY Interface”.

Does the M.2 M key on the bottom get the 4x PCIe v3, and the M.2 E key on the top get the 1x PCIe v2?

. (cnx-software.com)

Oh wait a bit, reading the main Rock5 thread, I see a mentioning that there are more Rock5 variants and that one or both, use the “RK3588S” which is a limited RK3588 variant which only has 2x one PCIe v2 in total, is it?

Please clarify which Rock5 variants exist, and do they use RK3588S or RK3588?

(Cautionary note: There is also a “Rock5 Compute Module” and its specs are here https://wiki.radxa.com/Rock5/CM5 . That one is different altogether from the Rock5 SBC. Note that one is pin compatible with the Raspberry 4 Compute Module, and indeed it offers 2x PCIe v2 lanes.)

Oh and then, if the lower M.2 is indeed 4x PCIe v3 lanes, in this situation:

Is it possible to bifurcate that M.2 slot into two separate M.2 slots that each get 2x PCIe v3 lanes only, or would a separate PCIe switch chip be needed to accomplish that?

ROCK 5B has:

  • 1x M.2 M Key, PCIe 3.0 x4 lanes, for NVMe SSD
  • 1x M.2 E Key, PCIe 2.1 x1 lanes, for WiFi6
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Thanks @jack. Now you also double-confirmed that the Rock5 SBC “model B” has the RK3588 and not RK3588S, thanks.

Also I learned from @stuartiannaylor’s post in other thread that

  • Bifurcation is possible indeed (of the lower M.2) to both two devices x 2 lanes each and to four devices x 1 lanes each.

  • About Rock5 models: There is only “model B” (the SBC) and “Compute Module”. The “model A” stopped at the idea stage, it doesn’t exist.

Hi @rock - I don’t know about ROCK5 Model A for certain, but I know in the Raspberry Pi world the Model B (most people want this) usually launches first, then they go back and create the Model A for the niche users. It may be the same for Radxa, but also they may just be going with RPi standard naming (since it’s de facto industry standards) that Model B = the flagship model.

It’s my understanding a ROCK5-based Compute Module is in the works - that’ll use the RK3588S you mention, possibly the cause for confusion.

Thanks for all your research on the PCIe lanes - this has been a question on my mind too.