1. SAS-3 Backchannel Revised T10/11-044r0
Harvey Newman
January 7, 2011

2. Overview
10-025r0 2010/01/07 SAS-3 SPL Back Channel Harvey Newman, Brian Day
Original presentation
10-090r1 2010/07/13 SPL-2 Backchannel Speed Negotiation Brian Day
Additional details including state machine changes
10-356r0 2010/11/04 SAS-3 Back Channel Train-SNW to Phy_Ready Tim Symons
Page 2 “When both phys are trained, then transition directly to SP15 (Phy_Ready) state.”
Tx train complete over Backchannel represents Tx is complete but not dword sync.
See the initial concept further explained in r0
10-357r0 2010/11/04 SAS-3 Maximum Back Channel Training time Tim Symons
Define convergence
Quantify coefficient weights
10-358R0 2010/11/04 SAS-3 Back Channel Tx default coefficients Tim Symons
Allow devices to implement a default state
Now covered by r0
T10/11-044r0

3. Training Complete Indicates Transmitter Coefficients Adjusted But Does Not Mean Phy Ready

4. Review Backchannel Adaptation
T10/11-044r0

5. Training Complete Response to 10-356r0
1 = Transmitter training is complete or not requested.
It is valid to enter the backchannel training process and have the status report training complete due to not requested. This can be the case where training has taken place previously and it knows the infrastructure has not changed.
Only invalid comma characters sent during backchannel.
Comma = or needs to start at 40 bit boundary.
Only 20 ones followed by 20 zeros then 16 Manchester encoded characters with a cell boundary of 10 bits.
None of these can be used for dword sync (DWS) because they are in the wrong location.
Scrambled 0 contain no comma characters.
At this point we have not received a single comma character to allow DWS. There is no way to transition to phy ready.
Any attempt to achieve DWS at this stage is just overhead and extends training time. SAS already has a perfectly good DWS method and we want to reuse existing state machines.
T10/11-044r0

6. Proposed backchannel complete skips TrainSNW. DWS has not been achieved.

7. Speed negotiation flow chart SPL and adding backchannel
Update to Train SNW
T10/11-044r0

8. Maximum Backchannel Training Time
10-357r0 2010/11/04 SAS-3 Maximum Back Channel Training time Tim Symons
Page 2 request to define convergence
Vendor specific for Backchannel SP34: Tx_Train but required to be at an operating point to support 1e-15 BER by completion of SP30: TrainingDone. Internal functionality not measureable or verifiable.
Page 4 Quantify coefficient weights
“Range and number of coefficient weighting steps.”
1200mV(pp) max amplitude for emphasized bit. Step size is 5mV to 20mV.
Handshake using the backchannel notifies when limits are reached.
“Maximum Training time”
500ms for worst case and only applies to failure mode.
Protocol round trip takes <1us per step.
For example: It takes 1.2ms to step over half the range given the smallest set size and 10us Rx decision period.
Training will take far less time a second time.
“Provide method to allow coefficient steps to make non-incremental “jumps” to values accelerate convergence.”
Multiple single steps can be applied quickly to achieve the same result.
More complex decoding for no added functionality
T10/11-044r0

9. Review Proposal
T10/11-044r0

10. Non-incremental jumps and the uncertainty
Non-incremental jumps and the uncertainty. Where will you be even after 5 jumps?
T10/11-044r0

11. Revised Proposal for SAS Control Register
Index
Name
Values
15:14
Coefficient settings
11b = Reserved
10b = Default coefficients (set by manufacturer)
01b = Set Tx to a specified operating condition to be determined by the phy committee (Reference)
(Not persistent across reset, reference Tx mode for characterization)
00b = Normal operation (up to Tx to determine, may use default or last know value)
13:6
Reserved
Write as zero, ignore on read
5:4
Coefficient (+1) update request
5 4
1 1 = Reserved
1 0 = Decrement
0 1 = Increment
0 0 = Hold
3:2
Coefficient (0) update request
Encoding per coefficient (+1) update request
1:0
Coefficient (-1) update request
T10/11-044r0

12. Training at 12Gbps
T10/11-044r0

13. LSI Proprietary