Motherboard provides more USB ports than B450? (lemmy.ml)

submitted 11 months ago by glibg10b@lemmy.ml to c/techsupport@lemmy.world

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My motherboard provides 4x USB 3.2 Gen1 ports for rear I/O and another 2x USB 3.2 Gen1 ports for front I/O (through the header), but my chipset only supports 2x USB 3.2 Gen1 ports. Where is the support for the other ports coming from?

Motherboard	Wikipedia

The motherboard is an ASRock B450M Steel Legend

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[-] SteveTech@programming.dev 2 points 11 months ago

It seems like only 5 of 6 chipset PCIe lanes are exposed on the board, so it's totally possible that they used the extra x1 for a USB card.

(The Gen 3 slots come off the CPU, so aren't counted)

[-] glibg10b@lemmy.ml 2 points 11 months ago* (last edited 11 months ago)

Ah, I think I'm starting to understand this a little better. Is that 4 lanes for SATA and 1 for the PCIe x1 slot?

Where do you reckon the PCIe 2.0 x16 slot's lanes come from?

[-] SteveTech@programming.dev 2 points 11 months ago* (last edited 11 months ago)

Nah SATA is built into the chipset. That second x16 is actually only electrically x4 in an x16 form factor, and there's that x1 slot, adding up to 5 lanes in total. The first x16 and first nvme slot (x4) are connected to the CPU directly (which IIRC most have 20 lanes on AM4, but not always).

[-] glibg10b@lemmy.ml 1 points 11 months ago* (last edited 11 months ago)

Oh, that makes sense, thanks

My CPU (1600 AF) only has 16 lanes, but I have a graphics card and an NVMe SSD and both seem to be getting all the lanes. I wonder what's going on here

07:00.0 VGA compatible controller: NVIDIA Corporation TU116 [GeForce GTX 1650 SUPER] (rev a1) (prog-if 00 [VGA controller])
       Subsystem: Micro-Star International Co., Ltd. [MSI] TU116 [GeForce GTX 1650 SUPER]
               [...]
               LnkCap: Port #0, Speed 8GT/s, Width x16, ASPM L0s L1, Exit Latency L0s &lt;1us, L1 &lt;4us
                       ClockPM+ Surprise- LLActRep- BwNot- ASPMOptComp+
               LnkCtl: ASPM Disabled; RCB 64 bytes, Disabled- CommClk+
                       ExtSynch- ClockPM+ AutWidDis- BWInt- AutBWInt-
               LnkSta: Speed 8GT/s (ok), Width x16 (ok)
                       TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-

01:00.0 Non-Volatile memory controller: Silicon Motion, Inc. SM2262/SM2262EN SSD Controller (rev 03) (prog-if 02 [NVM Express])
       Subsystem: Silicon Motion, Inc. SM2262/SM2262EN SSD Controller
               [...]
               LnkCap: Port #0, Speed 8GT/s, Width x4, ASPM L1, Exit Latency L1 &lt;8us
                       ClockPM+ Surprise- LLActRep- BwNot- ASPMOptComp+
               LnkCtl: ASPM Disabled; RCB 64 bytes, Disabled- CommClk+
                       ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
               LnkSta: Speed 8GT/s (ok), Width x4 (ok)

Full output

Edit:

$ sudo dmidecode --type 9 | grep -E 'Usage|Type|Designation'
	Designation: PCIE1
	Type: x1 PCI Express
	Current Usage: In Use
	Designation: PCIE2
	Type: x16 PCI Express
	Current Usage: In Use
	Designation: PCIE3
	Type: x1 PCI Express
	Current Usage: In Use
	Designation: PCIE4_M2_1
	Type: x4 PCI Express
	Current Usage: In Use

[-] SteveTech@programming.dev 1 points 11 months ago

Huh that's interesting, I believe that GPU should've been running at x8 with that CPU, but if it works then whatever I suppose.

I believe there are PCIe bandwidth benchmarks, if you really want to confirm, but I wouldn't worry.

Also it isn't uncommon for the device to just report the wrong speed, for example my Intel Arc reports running at x1, but benchmarks show otherwise.

this post was submitted on 10 Dec 2023

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