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USB4

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USB4
Type USB
Production history
Designer USB Promoter Group
Designed 29 August 2019; 5 years ago (2019-08-29)
Superseded USB 3.2
Daisy chain No
Audio signal DisplayPort
Video signal DisplayPort
Connector USB-C
Electrical
Max. voltage 48 V (PD 3.1)
Max. current 5 A (PD)
Data
Data signal Yes
Bitrate 40 Gbit/s (5 GB/s)
USB4 Gen3x2 cable (40 Gbps) with 100 W Power Delivery

USB4 (official style), sometimes referred to as USB 4.0, is a technical specification that the USB Implementers Forum (USB-IF) has first released on 29 August 2019.[1] USB4 is based on the Thunderbolt 3 protocol specification, which Intel has donated to the USB-IF.[2] The USB4 architecture can share a single, high-speed link with multiple hardware endpoints dynamically, best serving each transfer by data type and application.

In contrast to prior USB protocol standards, USB4 mandates the exclusive use of the Type-C connector and USB Power Delivery (USB-PD) specification. USB4 products must support 20 Gbit/s throughput and can support 40 Gbit/s throughput, but because of tunneling, even nominal 20 Gbit/s can result in higher effective data rates in USB4, compared to USB 3.2, when sending mixed data. In contrast to USB 3.2, it allows tunneling of DisplayPort and PCI Express.

Support of interoperability with Thunderbolt 3 products is optional for USB4 hosts and USB4 peripheral devices; but is mandatory for USB4 hubs on all of their downstream facing ports (DFP), and for USB4-based docks, on their upstream facing port (UFP) in addition to all of their downstream facing ports.[3] On the other hand, support for USB4 is required in Thunderbolt 4.[4]

The USB4 2.0 specification was released on October 18, 2022, by the USB Implementers Forum, delivering 80 Gbits/s and even 120 Gbit/s in asymmetric mode.[5]

History

USB4 was announced in March 2019.[6][7] The USB4 specification version 1.0, released 29 August 2019, uses "Universal Serial Bus 4" and specifically "USB4", that is the short name branding is deliberately without a separating space versus the prior versions. Several news reports before the release of that version use the terminology "USB 4.0" and "USB 4".[8][9] Even after publication of rev. 1.0, some sources write "USB 4", claiming "to reflect the way readers search".[10]

On 1 September 2022, the USB Promoter Group announced the pending release of the USB4 Version 2.0 specification, and the specification was subsequently released on 18 October 2022.[11][12]

At time of publication of version 1.0, promoter companies having employees that participated in the USB4 Specification technical work group were: Apple Inc., Hewlett-Packard, Intel, Microsoft, Renesas Electronics, STMicroelectronics, and Texas Instruments.

Goals stated in the USB4 specification are increasing bandwidth, helping to converge the USB-C connector ecosystem, and "minimize end-user confusion". Some of the key areas to achieve this are using a single USB-C connector type, while retaining compatibility with existing USB and Thunderbolt products.[13]

On 29 April 2020, DisplayPort Alt Mode version 2.0 was released, supporting DisplayPort 2.0 over USB4.[14]

Data transfer modes

USB4 by itself does not provide any generic data transfer mechanism or device classes like USB 3.x, but serves mostly as a way to tunnel other protocols like USB 3.2, DisplayPort, and optionally PCIe. While it does provide a native Host-to-Host protocol, as the name implies it is only available between two connected hosts; it is used to implement Host IP Networking. Therefore, when the host and device do not support optional PCIe tunneling, the maximum non-display bandwidth is limited to USB 3.2 20 Gbit/s, while only USB 3.2 10 Gbit/s is mandatory.

USB4 specifies tunneling of:

USB4 also requires support of DisplayPort Alternate Mode. That means, DP can be sent via USB4 tunneling or by DP Alternate Mode.[15]

DisplayPort Alt Mode 2.0: USB 4 supports DisplayPort 2.0 over its alternative mode. DisplayPort 2.0 can support 8K resolution at 60 Hz with HDR10 color and can use up to 80 Gbit/s which is the same amount available to USB data, but just unidirectional.[16]

Legacy USB (1–2) is always supported using the dedicated wires in the USB-C connector.

Some transfer modes are supported by all USB4 devices, support for others is optional. The requirements for supported modes depend on the type of device.

Transfer mode support by endpoints[1]
Mode Host Hub Peripheral device
Legacy USB (1–2) (max. 480 Mbit/s) Yes Yes Yes
USB4 20 Gbit/s Transport Yes Yes Optional
USB4 40 Gbit/s Transport Optional Yes Optional
Tunneled USB 3.2 (10 Gbit/s) Yes Yes Yes
Tunneled USB 3.2 (20 Gbit/s)[17] Optional Optional Optional
Tunneled Displayport Yes Yes Optional
Tunneled PCI Express Optional Yes Optional
Host-to-Host communications Yes Yes —
DisplayPort Alternate Mode Yes Yes Optional
Thunderbolt Alternate Mode Optional Yes Optional
USB-C Alternate Modes Optional Optional Optional
Comparison of transfer modes
Mode Name Old Name Encoding Multiple Lanes Lane Speed
(Gbit/s) 		Nominal Speed USB-IF Marketing Name[18][19] Logo
(Gbit/s) (GB/s)
USB 3.2 Gen 1×1 USB 3.0,
USB 3.1 Gen 1 		8b/10b Single 5 5 0.625 SuperSpeed USB 5Gbps
USB 3.2 Gen 1×2 Does not appear Dual 5 10 1.2 —
USB 3.2 Gen 2×1 USB 3.1 Gen 2 128b/132b Single 10 10 1.2 SuperSpeed USB 10Gbps
USB 3.2 Gen 2×2 Does not appear Dual 10 20 2.4 SuperSpeed USB 20Gbps
USB4 Gen 2×1 64b/66b[a] Single 10 10 1.2 —
USB4 Gen 2×2 Dual 10 20 2.4 USB4 20Gbps
USB4 Gen 3×1 128b/132b[a] Single 20 20 2.4 —
USB4 Gen 3×2 Dual 20 40 4.8 USB4 40Gbps
USB4 Gen 4×1 PAM-3[20] Single 40 40 4.8 —
USB4 Gen 4×2 Dual 40 80 9.6 USB4 80Gbps
USB4 Gen 4 Asymmetric Triple 40 120 14.4 USB4 120Gbps
  1. ^ a b USB4 can use optional Reed–Solomon forward error correction (RS FEC). In this mode, 12 × 16 B (128 bit) symbols are assembled together with 2 B (12 bit + 4 bit reserved) synchronisation bits indicating the respective symbol types and 4 B of RS FEC to allow to correct up to 1 B of errors anywhere in the total 198 B block.

USB4 Gen 2 is different from USB 3.2 Gen 2. They only signify the same speed, i.e. 10 Gbit/s, but they are coded differently on the electrical layer.

Although USB4 is required to support dual-lane modes, it uses single-lane operations during initialization of a dual-lane link; single-lane link can also be used as a fallback mode in case of a lane bonding error.

In Thunderbolt compatibility mode, the lanes are driven slightly faster at 10.3125 Gbit/s (for Gen 2) and 20.625 Gbit/s (for Gen 3), as required by Thunderbolt specifications (these are called legacy speeds and rounded speeds[21]). After removal of 64b/66b encoding, those also become round, 20.625/66*64 = 20.000 Gbit/s.

Power delivery

USB4 requires USB Power Delivery (USB PD). A USB4 connection needs to negotiate a USB PD contract before being established. A USB4 source must at least provide 7.5 W (5 V, 1.5 A) per port. A USB4 sink must require less than 250 mA (default), 1.5 A, or 3 A @ 5 V of power (depending on USB-C resistor configuration) before USB PD negotiation. With USB PD, up to 240 W of power is possible with 'Extended power range' (5 A at 48 V). For 'Standard Power range' up to 100 W is possible (5 A at 20 V).

Thunderbolt 3 compatibility

The USB4 specification states that a design goal is to "Retain compatibility with existing ecosystem of USB and Thunderbolt products." Compatibility with Thunderbolt 3 is required for USB4 hubs; it is optional for USB4 hosts and USB4 peripheral devices.[22] Compatible products need to implement 40 Gbit/s mode, at least 15 W of supplied power, and the different clock; implementers need to sign the license agreement and register a Vendor ID with Intel.[23]

Pinout

Type-C receptacle pinout (end-on view)

USB4 has 24 pins in a symmetrical USB type C shell. USB4 has 12 A pins on the top and 12 B pins on the bottom.[24]

USB4 has two lanes of differential SuperSpeed pairs. Lane one uses TX1+, TX1-, RX1+, RX1- and lane two uses TX2+, TX2-, RX2+, RX2-. USB4 transfers data at 20 Gbp/s per lane. USB4 also keeps the differential D+ and D- for USB 2.0 transfer.[25]

The CC configuration channels have the roles of creating a relationship between attached ports, detecting plug orientation due to the reversible USB type C shell, discovering the VBUS power supply pins, determining the lane ordering of the SuperSpeed lanes, and finally the USB protocol makes the CC configuration channel responsible for entering USB4 operation.[26]

Type-C receptacle A pin layout
Pin Name Description
A1 GND Ground return
A2 SSTXp1 ("TX1+") SuperSpeed differential pair #1, TX, positive
A3 SSTXn1 ("TX1-") SuperSpeed differential pair #1, TX, negative
A4 VBUS Bus power
A5 CC1 Configuration channel
A6 Dp1 USB 2.0 differential pair, position 1, positive
A7 Dn1 USB 2.0 differential pair, position 1, negative
A8 SBU1 Sideband use (SBU)
A9 VBUS Bus power
A10 SSRXn2 ("RX2-") SuperSpeed differential pair #4, RX, negative
A11 SSRXp2 ("RX2+") SuperSpeed differential pair #4, RX, positive
A12 GND Ground return
Type-C receptacle B pin layout
Pin Name Description
B12 GND Ground return
B11 SSRXp1 SuperSpeed differential pair #2, RX, positive
B10 SSRXn1 SuperSpeed differential pair #2, RX, negative
B9 VBUS Bus power
B8 SBU2 Sideband use (SBU)
B7 Dn2 USB 2.0 differential pair, position 2, negative[a]
B6 Dp2 USB 2.0 differential pair, position 2, positive[a]
B5 CC2 Configuration channel
B4 VBUS Bus power
B3 SSTXn2 SuperSpeed differential pair #3, TX, negative
B2 SSTXp2 SuperSpeed differential pair #3, TX, positive
B1 GND Ground return
  1. ^ a b There is only a single non-SuperSpeed differential pair in the cable. This pin is not connected in the plug/cable.

Software support

USB4 is supported by:

Hardware support

During CES 2020, USB-IF and Intel stated their intention to allow USB4 products that support all the optional functionality as Thunderbolt 4 products. The first products compatible with USB4 were Intel's Tiger Lake processors, with more devices appearing around the end of 2020.[30][31]

Brad Saunders, CEO of the USB Promoter Group, anticipates that most PCs with USB4 will support Thunderbolt 3, but for phones the manufacturers are less likely to implement Thunderbolt 3 support.[10]

On 3 March 2020, Cypress Semiconductor announced new Type-C power (PD) controllers supporting USB4, CCG6DF as dual port and CCG6SF as single-port.[32]

In November 2020, Apple unveiled MacBook Air (M1, 2020), MacBook Pro (13-inch, M1, 2020), and Mac mini (M1, 2020) featuring two USB4 ports.

List of Apple devices featuring USB4 ports include:[33]

  • MacBook Air (M2, 2022)
  • MacBook Pro (13-inch, M2, 2022)
  • iMac (24-inch, M1, 2021)
  • MacBook Pro (13-inch, M1, 2020)
  • MacBook Air (M1, 2020)
  • Mac mini (M1, 2020)

AMD also stated that Zen3+ (Rembrandt) processors will support USB4.[34] However, AMD has only announced support for USB 3.2 Gen2x2 in Zen 4 processors that were released in September 2022.[35][36]

References

  1. ^ a b "USB Promoter Group USB4 Specification". USB implementers forum. 2019-08-29. Archived from the original on 2021-02-13. Retrieved 2020-04-28.
  2. ^ Bright, Peter (2019-03-04). "Thunderbolt 3 becomes USB4, as Intel's interconnect goes royalty-free". Ars Technica. Archived from the original on 2021-02-13. Retrieved 2019-03-04.
  3. ^ see 2.1.5 (page 15) in https://www.usb.org/sites/default/files/USB4%20Specification.zip
  4. ^ Introducing Thunderbolt 4: Universal Cable Connectivity for Everyone Archived 22 November 2021 at the Wayback Machine. Intel newsroom. July 8, 2020
  5. ^ "USB Promoter Group Announces USB4 Version 2.0 Specification defines delivering up to 80 Gbps over USB Type-C" (PDF).
  6. ^ Hill, Brandon (2019-03-04). "USB4 Leverages Thunderbolt 3 Protocol Doubling Speeds To 40Gbps". HotHardware. Archived from the original on 2021-10-23. Retrieved 2020-04-28.
  7. ^ "USB4 announced with 40Gbps bandwidth, it's based on Thunderbolt 3". GSMArena.com. Archived from the original on 2022-01-15. Retrieved 2020-04-29.
  8. ^ "With USB 4, Thunderbolt and USB will converge". 2019-03-04. Archived from the original on 2022-09-10. Retrieved 2020-05-01.
  9. ^ Hagedoorn, Hilbert. "USB 4.0 Will Arrive in Late 2020". Guru3D. Archived from the original on 2021-10-26. Retrieved 2020-04-30.
  10. ^ a b September 2019, Avram Piltch 03 (2021-04-20). "USB 4: Everything We Know So Far". Tom's Hardware. Archived from the original on 2021-06-30. Retrieved 2020-04-30.{{cite web}}: CS1 maint: numeric names: authors list (link)
  11. ^ "USB Promoter Group Announces USB4 Version 2.0". www.businesswire.com. 2022-09-01. Archived from the original on 2022-09-02. Retrieved 2022-09-02.
  12. ^ "USB-IF Announces Publication of New USB4® Specification to Enable USB 80Gbps Performance" (PDF). USB-IF. USB Implementers Forum. 2022-10-18. Retrieved 2023-01-19.
  13. ^ USB4 Spec. p.1
  14. ^ Association (VESA), Video Electronics Standards. "VESA Releases Updated DisplayPort Alt Mode Spec to Bring DisplayPort 2.0 Performance to USB4 and New USB Type-C Devices". www.prnewswire.com. Archived from the original on 2021-11-24. Retrieved 2020-04-30.
  15. ^ "USB4 - No more Mr. Nice Guy, your USB-C connector has to do it all! - #38". YouTube. 2019-11-21. Archived from the original on 2021-11-25. Retrieved 2020-05-01.
  16. ^ "VESA RELEASES UPDATED DISPLAYPORT ALT MODE SPEC TO BRING DISPLAYPORT 2.0 PERFORMANCE TO USB4 AND NEW USB TYPE-C DEVICES". Vesa. 2020-04-29. Archived from the original on 2021-11-23. Retrieved 2021-08-09.
  17. ^ USB4 Spec 1.0 Sect 9 specifically mentions the requirement of "Superspeed Plus (= Gen 2×1) support for hubs and devices, the latter only if they optionally support USB3 tunneling. The rest of the specification doesn't mention the speed at all, and more generically just refers to the whole USB 3.2 architecture as "Enhanced Superspeed". Section 9.2.1 states the requirement to only support Gen 2×1 for the USB3 tunneling adapter, with Gen 2×2 being optional.
  18. ^ "USB 3.2 Specification Language Usage Guidelines from USB-IF" (PDF). Archived (PDF) from the original on 2021-11-03. Retrieved 2021-11-13.
  19. ^ "USB4 Specification Language Usage Guidelines from USB-IF" (PDF). Archived (PDF) from the original on 2021-11-13. Retrieved 2021-11-13.
  20. ^ GraniteRiverLabs, Team (2023-01-17). "Welcome to the 80Gpbs Ultra-High Speed Era of USB4 | GraniteRiverLabs Taiwan". www.graniteriverlabs.com. Archived from the original on 2023-02-21. Retrieved 2023-02-21.
  21. ^ "How to Test and Troubleshoot USB4" (PDF). Archived (PDF) from the original on 2022-09-10. Retrieved 2022-07-25.
  22. ^ USB4 Specification V1.0 August 2019 Chapter 13: "A USB4 host and USB4 peripheral device may optionally support TBT3-Compatibility. If a USB4 host or USB4 peripheral device supports TBT3-Compatibility, it shall do so as defined in this chapter".
  23. ^ "USB4 Thunderbolt3 Compatibility Requirements Specification - USB-F". Archived from the original on 2021-11-24. Retrieved 2021-11-13.
  24. ^ "The Relationship Between USB4 and the USB Type-C Connector". Total Phase Blog. 2020-02-18. Archived from the original on 2022-09-10. Retrieved 2022-04-05.
  25. ^ "USB4 Specification". www.usb.org. Archived from the original on 2022-04-14. Retrieved 2022-04-05.
  26. ^ Leung, Benson (2018-11-19). "USB Type-C™'s Configuration Channel". Medium. Archived from the original on 2022-04-05. Retrieved 2022-04-05.
  27. ^ "Linux 5.6 Kernel Released With WireGuard, USB4, New AMD + Intel Hardware Support - Phoronix". Phoronix.com. Archived from the original on 2021-11-02. Retrieved 2020-04-28.
  28. ^ "Introducing the next generation of Mac". apple.com. 2020-11-10. Archived from the original on 2021-03-01. Retrieved 2020-11-13.
  29. ^ windows-driver-content. "Introduction to the USB4 connection manager in Windows". docs.microsoft.com. Archived from the original on 2021-11-03. Retrieved 2021-11-03.
  30. ^ "USB4 devices are clear to roll out next year". Engadget. Archived from the original on 2021-11-24. Retrieved 2020-04-28.
  31. ^ Maislinger, Florian (2019-06-14). "First USB 4 devices to be launched at the end of 2020". Archived from the original on 2021-11-24. Retrieved 2020-04-28.
  32. ^ Shilov, Anton. "Cypress Announces USB 3.2 & USB4-Ready Controllers: EZ-PD CCG6DF & CCG6SF". www.anandtech.com. Archived from the original on 2021-12-06. Retrieved 2020-04-28.
  33. ^ "Identify the ports on your Mac". Apple Support. Archived from the original on 2022-09-04. Retrieved 2022-09-06.
  34. ^ Cutress, Ian (2022-01-04). "AMD Announces Ryzen 6000 Mobile CPUs for Laptops: Zen3+ on 6nm with RDNA2 Graphics". Anandtech. Archived from the original on 2022-06-25. Retrieved 2022-07-26.
  35. ^ Bonshor, Gavin (2022-05-23). "AMD Ryzen 7000 Announced: 16 Cores of Zen 4, Plus PCIe 5 and DDR5 for Socket AM5, Coming This Fall". Anandtech. Archived from the original on 2022-07-26. Retrieved 2022-07-26.
  36. ^ "AMD confirms Zen4 & Ryzen 7000 series lineup: Raphael in 2022, Dragon Range and Phoenix in 2023". VideoCardz.com. Retrieved 2022-11-29.
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