UNH InterOperability Lab
Serial Attached SCSI (SAS)
Clause 5 Considerations
Improving Networks Worldwide.
Improving Networks Worldwide.
SAS Clause 5 Considerations
Presentation Topics
• Transmission Speeds and Unit Intervals
• OOB Construction
• Differential Signaling
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SAS Clause 5 Considerations
Physical Link Rate (Nominal)
• 1.5 Gbps SAS
– 150 MBps (MegaBytes Per Second)
• 3.0 Gbps SAS
– 300 MBps
• 6.0 Gbps SAS
– 600 MBps
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SAS Clause 5 Considerations
Unit Intervals (Nominal)
• 1.5 Gbps SAS
– 666.66666 ps (picoseconds) = 2000/3 ps
• 3.0 Gbps SAS
– 333.33333 ps = 1000/3 ps
• 6.0 Gbps SAS
– 166.66666 ps = 500/3 ps
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SAS Clause 5 Considerations
Baud Rate (Nominal)
• 1.5 Gbps SAS
– 1.5 Gigasymbols/s
• 3.0 Gbps SAS
– 3.0 Gigasymbols/s
• 6.0 Gbps SAS
– 6.0 Gigasymbols/s
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SAS Clause 5 Considerations
OOB Signal Construction
• Out-Of-Band Signals
• Consists of Bursts Dwords and Gaps of
DC Idle
• Built with D24.3 characters
– 110011 0011
– 001100 1100
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SAS Clause 5 Considerations
OOB Interval
• Minimum
– 665.06666 ps = 666.66666 x (1 – 0.0024)
• Nominal
– 666.66666 ps
• Maximum
– 668.26666 ps = 666.66666 x (1 + 0.0024)
• 1 OOBI = 666.66666 ps (Nominal)
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SAS Clause 5 Considerations
OOB Signals
• Built from three parts:
– Bursts, Idles, Negations
• Three different signals
– COMWAKE
– COMINIT/COMRESET
– COMSAS
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SAS Clause 5 Considerations
COMWAKE
• SATA Signal
• Special use for new features in SAS-2
• Burst Time
– 160 OOBI (106.66666 ns)
• Idle Time
– 160 OOBI (106.66666 ns)
• Negation Time
– 280 OOBI (186.66666 ns)
• Total Signal Time
– 2200 OOBI (1466.6666 ns)
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SAS Clause 5 Considerations
COMWAKE
160 OOBI
Each
Total Time: 2200 OOBI
280 OOBI
160 OOBI
Each
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SAS Clause 5 Considerations
COMINIT/COMRESET
• SATA and SAS Signal
• Used to Initialize and Reset the entire
connection
• Burst Time
– 160 OOBI (106.66666 ns)
• Idle Time
– 480 OOBI (320 ns)
• Negation Time
– 800 OOBI (533.33333 ns)
• Total Signal Time
– 4640 OOBI (3093.3333 ns)
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SAS Clause 5 Considerations
COMINIT/COMRESET
160 OOBI
Each
480 OOBI
Each
800 OOBI
Total Time: 4640 OOBI
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SAS Clause 5 Considerations
COMSAS
• SAS Only Signal
• Used to communicate that a device is a SAS
device
• Burst Time
– 160 OOBI (106.66666 ns)
• Idle Time
– 1440 OOBI (960 ns)
• Negation Time
– 2400 OOBI (1600 ns)
• Total Signal Time
– 12000 OOBI (8000 ns)
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SAS Clause 5 Considerations
COMSAS
160 OOBI
Each
2400 OOBI
1440 OOBI
Each
Total Time: 12000 OOBI
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SAS Clause 5 Considerations
Detecting OOB Signals
• Signals are detected via Idle times NOT
Burst times
• Burst Tolerances
– MAY detect all any burst <= 100ns
– SHALL detect all bursts > 100ns
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SAS Clause 5 Considerations
Idle Time Detection Requirements
• COMWAKE
– MAY Detect
• 35 ns <= Tidle < 175 ns
– SHALL Detect
• 101.3 ns <= Tidle <= 112 ns
– SHALL NOT Detect
• Tidle < 35 ns
• Tidle >= 175 ns
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SAS Clause 5 Considerations
Idle Time Detection Requirements
• COMINIT/COMRESET
– MAY Detect
• 175 ns <= Tidle < 525 ns
– SHALL Detect
• 304 ns <= Tidle <= 336 ns
– SHALL NOT Detect
• Tidle < 175 ns
• Tidle >= 525 ns
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SAS Clause 5 Considerations
Idle Time Detection Requirements
• COMSAS
– MAY Detect
• 525 ns <= Tidle < 1575 ns
– SHALL Detect
• 911.7 ns <= Tidle <= 1008 ns
– SHALL NOT Detect
• Tidle < 525 ns
• Tidle >= 1575 ns
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SAS Clause 5 Considerations
Differential Signaling
• Used to aid in handling noise on the
line
• One + signal and one – signal
transmitting in each direction
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SAS Clause 5 Considerations
Differential Signaling
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SAS Clause 5 Considerations
Differential Signaling
• Negative Signal is subtracted from the
positive signal at the receiver
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SAS Clause 5 Considerations
Differential Signaling
• Result
– Because ‘opposite’ signals were
transmitted initially; output signal is twice
as powerful
– Noise will, theoretically, be applied equally
to both channels of the differential signal;
noise is eliminated from the output signal
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