PCIe USB 3.0 Extra Headers and Bandwidth Limitations?

[NarimaanV]

Hi,

        So I'm looking at a possible combination of motherboard and case and noticed a conflict in how many USB 3.0 headers the case needs vs how many the motherboard has. Motherboard I'm looking at is the Asus ROG Maximus IX Formula and the case is the Cooler Master Mastercase Maker 5t. First problem is, since the 5T has 4 USB 3.0 ports on the front, it needs 2 USB 3.0 headers and the Formula IX only has 1 (really wish they kept the 2 headers like the Formula VIII but that's besides the point). So to take advantage of all the front ports, I'd need something like this PCIe USB 3.0 expansion headers card. My question then stems from using an expansion card like that. Would adding USB 3.0 headers via a PCIe card like that affect bandwidth of using those ports? As in if I had every USB 3.0 port on the motherboard and case occupied, would I experience slower speeds due using more USB headers than came with the board? Also on the description page for the Formula IX, it says it's designed to have 6 USB 3.0 ports, 4 that come on the board and 2 via the header. If I used an expansion card like that which adds 4 ports on the front for a total of 8 ports instead of the rated 6, could that cause bandwidth-related slowdown issues from using more ports than it's designed to have? Thanks in advance!

[themctipers]

its going to effect it by a tiny bit, and latency but it will not really matter.

 

also, nope. no bandwidth related issues from using all devices at 100% capacity

[NarimaanV]

Awesome thank you! I really wish Asus would put less of their ports on the board itself and give you more headers for the case but oh well.

[mariushm]

The usb 3 header on the motherboard comes from the usb 3 controller built inside the chipset or from additional onboard usb3 controllers, which is then connected to the processor through a dedicated link.

The card will be connected to the motherboard through pci-e slot, some of these are connected directly to the processor, some are connected to the chipset (or the chipset creates these lanes).

 

That particular usb 3 card seems to use the Etron EJ198 chip, which creates 4 USB 3 ports each capable of 5 gbps (~ 600 MB/s). However, it communicates with the computer through two PCI-E v2.0 lanes, which means the maximum speed you'd have between the computer and the card (in both directions) would be 1000 MB/s, because each pci-e v2.0 lane is capable of maximum 500 MB/s

In addition, the slot seems to be the pci-e x4 connector (even though only 2 lanes can be used).  So, you can plug this card in a x4, x8 or x16 (physical) connector but no matter how many actual pci-e lanes that slot has (electrically), the chip can only communicate through 2 lanes.

 

On some motherboards, the x4 connectors are only physically x4 (in size) but electrically they're only x1. The controller is probably smart enough to work with just one pci-e lane, but then the maximum transfer speed of ALL usb 3.0 ports will be 500 MB/s, the limitation of the communication between motherboard and card. 

On some motherboards, the x4 slots can be configured from BIOS between x4 electrical or x1 electrical, or it switches automatically to x1 when you install an m.2 ssd in the special slot meant for those.

 

So basically, in best case scenario the maximum transfer speed between adapter card and pc would be 1000 MB/s - it's not a limitation if you use only one usb 3.0 connector at a time, but if you try to transfer from 2 or more connectors simultaneously, you'd see less than 600 MB/s from each connector. In real world, you'll probably see less than 300 MB/s.

More or less, not recommended to use such adapter cards with external SSD drives or real time capture cards or things that can transfer at very high speeds, they won't work at their maximum speed.

 

Using the card won't reduce the speed of the other usb 3 ports, those are connected differently and would be able to achieve the speeds they were designed for from the start.

[NarimaanV]

Well that's kinda unfortunate. Even though I know the chances are slim, I wouldn't want to have a setup like that and at some point in the distant future try to use something like a capture card on the front IO and not be able to figure out why its not running at optimal speed. It's really a shame because I've heard nothing but great things about Asus's ROG line of mobos, but the putting 4 of the 6 possible USB ports on the back kinda screws me using the 5T flawlessly. So my options end up being, change the motherboard or change the case, which sucks because both those go perfectly with the red/black theme build I had in mind (and the 5T is the nicest case I've found that has 5.25" drive bays and a tempered glass side-panel). The Formula is also perfect for starting out with an all air-cooled system and trying my hand at full water cooling down the line since it has water cooling capabilities built in. 

[NarimaanV]

Wait, are there any PCIe 3.0 based USB 3.0 header cards that could deliver the full speed with all the ports used at once or are they all PCIe 2.0 for the most part? 

[Electronics Wizardy]

12 minutes ago, NarimaanV said:

Wait, are there any PCIe 3.0 based USB 3.0 header cards that could deliver the full speed with all the ports used at once or are they all PCIe 2.0 for the most part? 

Don't worry about the speed. You won't use all the ports at full speed. Even the Intel controller can't do full speed on all ports. 

[NarimaanV]

2 minutes ago, Electronics Wizardy said:

Don't worry about the speed. You won't use all the ports at full speed. Even the Intel controller can't do full speed on all ports. 

So then would I want to plug the expansion card into a lane controlled by the processor or by the chipset on the motherboard? My gut would think the processor

[mariushm]

19 minutes ago, NarimaanV said:

Wait, are there any PCIe 3.0 based USB 3.0 header cards that could deliver the full speed with all the ports used at once or are they all PCIe 2.0 for the most part? 

Look for cards with AsMedia chips ...

 

Asmedia ASM1142 :  pci-e v2.0 x2 OR pci-e v3.0 x1  (1000 MB/s maximum speed)  to  2 x USB 3.1 (10 gbps) ports controller - it's the big brother of ASM1042 (pci-e v2.0 x1 to 2x5gbps usb 3)  commonly found on motherboards

 

So yeah, technically each connector can do 10 gbps or about 1.2 GB/s but you're limited by one pci-e lane (of 1000 MB/s) but if your devices are only 5gbps, then you'd do the 600 MB/s speed with one device plugged in, or maybe about 400-450 MB/s with two devices plugged in and transferring data at same time.

 

 

[Electronics Wizardy]

12 minutes ago, NarimaanV said:

So then would I want to plug the expansion card into a lane controlled by the processor or by the chipset on the motherboard? My gut would think the processor

Id use a chipset lane if you have one. No reason to use cpu lanes, the chipset has more than enough bandwidth, and usb3 is fairly low bandwidth.

[NarimaanV]

Awesome thanks for all that info!

[NarimaanV]

Okay so I found this which sounds amazing: http://www.silverstonetek.com/product.php?pid=619

 

It uses an ASMedia ASM1142 USB 3.1 controller, only has one header which is kinda annoying. So then my final question is, if I used two of these cards for the 4 ports on my front panel IO, do those ports become USB 3.1 ports or are they still limited to USB 3.0 speeds?

 

EDIT: There' apparently also a "revised version" of the card that adds chips to boost the signal for up to 2m of cable length but same concept as the original.

[mariushm]

They should work as usb 3.1 ... if there's too many errors (due to too long cable, or too cheap cable between connectors and card or something like that), it's probably going to automatically downgrade itself to usb 3.0 speeds.

The internal cable (from the case to the card) shouldn't be longer than around 50cm, so I don't think you need the "enhanced" card, but if the price difference isn't that great (the ReDriver chip is probably 1-3$ in 1000pcs orders so shouldn't add too much to the total price) then you should go for it. 

 

// off topic i honestly don't understand them... they added a sata connector just to get 5v for the usb connectors ... they have 12v in the pci-e slot and 3.3v , they could have used a dc-dc converter to create 5v from the 12v available in the slot (looks like there's even the footprints for components to do that on the board)

Guess a sata connector is cheaper than those components.

[NarimaanV]

19 minutes ago, mariushm said:

They should work as usb 3.1 ... if there's too many errors (due to too long cable, or too cheap cable between connectors and card or something like that), it's probably going to automatically downgrade itself to usb 3.0 speeds.

The internal cable (from the case to the card) shouldn't be longer than around 50cm, so I don't think you need the "enhanced" card, but if the price difference isn't that great (the ReDriver chip is probably 1-3$ in 1000pcs orders so shouldn't add too much to the total price) then you should go for it. 

That would be amazing! I really hope that works, always wanted USB 3.1 front IO

 

16 minutes ago, mariushm said:

// off topic i honestly don't understand them... they added a sata connector just to get 5v for the usb connectors ... they have 12v in the pci-e slot and 3.3v , they could have used a dc-dc converter to create 5v from the 12v available in the slot (looks like there's even the footprints for components to do that on the board)

Guess a sata connector is cheaper than those components.

Yeah even if it was cheaper to add a connector, why SATA of all things? Molex seemed more appropriate and easier to solder on there but what do I know 

[mariushm]

 

23 minutes ago, NarimaanV said:

 

Yeah even if it was cheaper to add a connector, why SATA of all things? Molex seemed more appropriate and easier to solder on there but what do I know 

Well, the pci express standard has some rules about how much power a card can take from slots.

 

There's three thresholds : 10w , 25w and 75w

 

PCI Express x1 cards are only allowed to use up to 10w of power which is from two sources : up to 3A from 3.3v and up to 0.5A from 12v, but in total from both sources it should not exceed 10 watts.

Half-Height cards are restricted to 10w, full height cards must start at 10w and then in theory they can "negociate" to be allowed to use up to 25w (in practice motherboard manufacturers always allow 25w, don't negociate anything)

 

PCI Express x4 cards can use up to 25w , again from 3.3v at max 3A and from 12v at max 2.1A 

 

The adapter card is physically a x4 slot, but being half height and considering it's using only 1 pci-e v3.0 lane or 2 pci-e v2.0 lane, according to the pci-e standard I guess it's classified in the 10w maximum section.

 

Each usb 3.1 slot is meant to provide 5v up to 0.9A to a device, so two devices would use up to 1.8A at 5v, or about 9w , however it's not uncommon for some devices (external hard drives etc) to use up to 2A by themselves.. so it's not a good idea to restrict the maximum current on each connector to exactly 0.9A.

 

So basically, the idea is that after budgeting about 2w for the controller chip and whatever else is on the card, you're left with about 8w of power out of that 10w budget which is not enough to feed both usb connectors with. If you want to be strict and respect the standard, you'd have to take these 8w from 3.3v and use a boost dc-dc converter to convert the 3.3v to 5v, and such a boost converter would have an efficiency of about 90%, so your turn 8w of 3.3v into about 7w at 5v ... or about 1.4A or 0.7A per connector, which is obviously not enough.

 

If the card pretends to be an x4 card and assume it's allowed to have a 25w budget, it could use the 12v at 2.1A and use about 20w of that budget to convert to 5v and you'd have almost 4A at 5v for the two connectors. 

Most regular people wouldn't care, and motherboards are already designed to handle this much power in any connector. It's just the pci-e standard people that are "stick in the mud".

 

If they catch you or someone complains that you're not respecting the standard, you risk getting fined by pci-e standard organization and they'd force you to not mention pci-e on packaging and the card and technically, it's not a valid pci-express adapter.

 

So basically the sata connector is a workaround... each pin in the connector is rated for up to 1.5A, so technically, the card can take in up to 4.5A  from 3.3v (if the power supply has it), 5v and 12v .. my guess is they feed the usb ports directly from the 5v in the sata connector.

[NarimaanV]

Wow well that's actually pretty interesting. So it all comes down to meeting standards then.