Anand Shirahatti is the CTO of Arrow Devices. He has been instrumental in making the company a leading provider of Verification, Validation and Debug Solutions. He has over 15 years of experience in design and verification. Most recently, he was a Senior Design Engineer at Nvidia. Arrow Devices … More »
Developing USB 3.1 IP? Essential Updates To USB 3.0 You Need To Know
November 4th, 2014 by Anand Shirahatti
Initially, USB provided two speeds (12 Mbps and 1.5 Mbps). With rapid adoption and success of the USB standard and the increasing power of PCs and computing devices, the USB 2.0 specification was defined in the year 2000. USB 2.0 provided upto 480 Mbps of bandwidth while keeping software compatibility with earlier USB applications. With ever increasing bandwidth requirements, in 2008 the USB 3.0 specification (providing 5 Gbps bi-directional bandwidth) was released. USB 3.1 is the next logical step in this progression. It provides 10Gbps of bi-directional bandwidth while maintaining backward compatibility with previous USB versions. To know more about USB 3.1 Verification solution click here.
In this post, we will analyze the technical differences between the USB 3.1 and USB 3.0 specifications. The aim is to enable people familiar with USB 3.0 to quickly understand the main aspects of USB 3.1.
We will analyze the PHY, Link and Protocol layers and list out the major ways in which USB 3.1 differs from USB 3.0.
The USB 3.1 specification refers the USB 3.0 PHY as Gen1 PHY and the USB 3.1 PHY as the Gen2 PHY.
1. Gen2 PHY uses a protocol over LFPS signaling to negotiate to highest common data rate of two connected PHYs
2. Encoding: Gen2 PHY uses 128b132b encoding while Gen1 PHY uses 8b10b encoding. This new encoding has lesser overhead and hence is more bandwidth efficient
3. Gen1 Link needs to transmit D/K codes while Gen2 Link needs to transmit Data and Block-Header
4. Gen1 Scrambler: G(X) = X16 + X5 + X4 + X3 + 1
Gen2 Scrambler: G(X) = X23 + X21 + X16 + X8 + X5 + X2 + 1
5. Gen2 introduces some new symbols (Table 6-1). Usage is summarized in the link layer section:
6. Gen2 Link Initialization & Training has an additional step: “Block alignment”
7. Gen2 SKP Ordered Set is different from Gen1. SKPEND allows receiver to identify location of next block header
8. PingLFPS for SuperSpeedPlus has new max value of tBurst
9. SuperSpeedPlus Capability Declaration is done while in Polling.LFPS state using SCD1 and SCD2 patterns
10. SuperSpeedPlus allows Binary Representation of Polling LFPS: logical 0 and 1 can be transmitted to receiver by varying the LFPS’s tRepeat
11. SCD1 and SCD2 are transmitted using Binary Representation of Polling.LFPS
12. SuperSpeedPlus allows LBPM: An LFPS based PWM messaging mechanism:
1. Differences in DPH: For SuperSpeedPlus USB, all header packets except for non-deferred DPH are the same as SuperSpeed USB. The non-deferred SuperSpeedPlus DPH is a header packet with its own framing ordered set, and contains a length field replica immediately after the Link Control word. The purpose of this special construction is to allow the non-deferred SuperSpeedPlus DPH to be processed differently from all other header packets and to achieve single bit error tolerance in its length field.
2. Header packet framing is different for deferred and non-deferred DPHs in SuperSpeedPlus. In SuperSpeed, they are same.
4. While SuperSpeed operation allows premature termination of a DPP with DPPABORT Ordered Set, SuperSpeedPlus does not allow this. DPP boundary has to be preserved (Except if Warm Reset or Recovery occurs during DPP).
5. Changes in Link Commands for SuperSpeedPlus: LCRD link command is extended in SuperSpeedPlus:
6. SuperSpeedPlus defines Type1 and Type2 traffic classes. SuperSpeed has only one traffic class.
7. Type1 traffic class consists of the following packets:
Type2 traffic class consists of asynchronous DPs
8. SuperSpeedPlus Defines the Idle Symbol Ordered Set differently from SuperSpeed
9. Link Initialization for SuperSpeedPlus additionally requires Type2 Rx Buffer Credit Advertisement
10. SuperSpeedPlus additionally requires Link to maintain Type2 Rx Buffer Credit Count (both Local and Remote)
11. SuperSpeedPlus Link needs to maintain two CREDIT_HP_TIMERs (one for each of Type1 and Type2)
12. SuperSpeedPlus link needs to implement “Link Error Count” (Section 18.104.22.168). Except for UPstream ports in SuperSpeed operation, all ports SHALL implement Link Error Count
13. SuperSpeedPlus may optionally implement “Soft Error Count“
14. For SuperSpeedPlus operation, port shall transition to Polling.PortMatch upon detecting Training Sequence Error in Polling.Active or Polling.Configuration
15. Major LTSSM changes in SuperSpeedPlus: New Polling States
1. Precision Time Measurement is a new capability introduced in SuperSpeedPlus:
2. ACK TP changes in SuperSpeedPlus: Some new fields have been added:
3. A new Device notification TP type SUBLINK_SPEED, has been added.
4. DP changes in SuperSpeedPlus: Some new fields have been added:
5. ITP changes: A new field has been added:
6. SuperSpeedPlus Supports IN transfers with multiple IN endpoints simultaneously (Spec section 8.10.2)
7. SuperSpeedPlus Transaction Reordering
8. Some timers have been defined for IN transfers:
9. Invalid TP: one more condition has been added the checks performed to determine a valid TP
10. ISOC endpoints can send more ISOC data transfers per service interval:
We hope you find the above useful to get a quick technical introduction to USB 3.1!
More Updates: (Thanks to Jan Axelson of Lakeview Research)
A-1. USB 3.1 has more detailed requirements for receptacle back-shields (5.8.2) and for the standard-A receptacle, new requirements for ground tabs and grounding spring tabs. (22.214.171.124)
A-2. USB 3.1 removes USB 3.0’s specified color for each wire. (5.4.2)
A-3. And some new descriptors defined in USB 3.1: