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UNH InterOperability Lab
Serial ATA (SATA)
Clause 8: OOB and Phy Power States
Improving Networks Worldwide.
SATA Clause 8
Presentation Topics
• Interface Power States
• Asynchronous Signal Recovery
• OOB and Signature FIS return
• Power-On Sequence State Machine
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SATA Clause 8
Interface Power States
• Serial ATA interface power states are
controlled by:
– The device
– The host controller
• There are three Interface Power States
(see table on next slide)
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SATA Clause 8
Interface Power States
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SATA Clause 8
Asynchronous Signal Recovery
• Is optional
• Phys may support ASR for applications
where the usage model of device insertion
into a receptacle (power applied at the time of
insertion) does not apply
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SATA Clause 8
Asynchronous Signal Recovery
• What happens:
– When a signal is lost, both the host and
device can attempt to recover it
– Loss of signal can be determined by the
host or device.
– Loss of signal is represented as a transition
from PHYRDY to PHYRDYn (associated
with entry into states LS1: NoCommErr or
LS2: NoComm within Link Layer)
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SATA Clause 8
Asynchronous Signal Recovery
• What happens (continued)
– Note: negation of PHYRDY does not
always mean a loss of signal
– Recovery of signal is associated with exit
from state LS2: NoComm
– Either the device or host will attempt to
recover the signal
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SATA Clause 8
Asynchronous Signal Recovery
• Device:
– If the device attempts to recover the signal
before the host, it will issue a COMINIT
– The device will return its signature
following completion of the OOB sequence
which included COMINIT
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SATA Clause 8
Asynchronous Signal Recovery
• Host:
– If a host supports ASR, upon receiving an
unsolicited COMINIT from the device, it
will issue a COMRESET (to the device)
• Note:
– Unsolicited COMINIT: A COMINIT that
was not in response to a preceding
(immediately before) COMRESET
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SATA Clause 8
Asynchronous Signal Recovery
• Host:
– When COMRESET is sent to the device in
response to an unsolicited COMINIT:
• Host shall set Status register to 7Fh
• Host shall set all other Shadow Command
Block Registers to FFh
– When COMINIT is received in response to
COMRESET (associated with entry into
state HP2B:HR_AwaitNoCOMINIT)
• Shadow Status register value shall be set to FFh
or 80h to reflect that a device is attached
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SATA Clause 8
Unsolicited COMINT usage
• Informative
• Issuing COMRESET to a device causes
it to lose software settings
– If software settings preservation is
supported (SSP), this will not happen
• If COMRESET was due to ASR and
legacy mode software is in use
– Software does not replace lost software
settings
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SATA Clause 8
Unsolicited COMINT usage
• Note:
– Issuing a non-commanded COMRESET to
the device should be minimized
– Want to ensure correct operation with
legacy mode software
– Avoid inadvertent loss of critical software
settings
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SATA Clause 8
Unsolicited COMINT usage
• Original use was only for when the
signal is lost between the host and
device
• Host (based on Host Phy Initialization
Stat Machine) shall assume when
receiving an unsolicited COMINIT:
– A new device was connected OR
– The cable was unplugged and
communication was lost to the device
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SATA Clause 8
Unsolicited COMINT usage
• Proper Host response to an unsolicited
COMINIT is to issue a COMRESET
– This will put the device into a known state
• When device issues an unsolicited
COMINIT and the host responds with
COMRESET, the software settings of
the device could be changed
– Legacy mode software might not recover
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SATA Clause 8
Unsolicited COMINT usage
• The device should only issue an unsolicited
COMINIT when:
– Phy voltage threshold falls below the minimum
value OR
– Last resort in error recovery
• This will minimize potential exposure to
software loss issues
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SATA Clause 8
OOB and Signature FIS return
• Informative
• What happens:
– After an OOB sequence
– Only if the device recognized COMRESET
during the OOB
– Happens with devices compliant to older
revisions of SATA specification
– Result: devices may send a Register –
Device to Host FIS with the device
signature
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SATA Clause 8
OOB and Signature FIS return
• Solution:
– For compatibility with older devices
– Host may ensure a system power-on event
• Device always receives a valid COMRESET
after power is determined good at the device
– Note: hot plug aware software will ensure
device always receives a COMRESET on a
hot plug event
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SATA Clause 8
OOB and Signature FIS return
• One specific solution:
– Host workaround
– Perform following software procedure
when determining device presence (on
next slide)
– Note: other methods for ensuring the
device receives a COMRESET in these
conditions are possible
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SATA Clause 8
OOB and Signature FIS return
• Possible Solution:
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SATA Clause 8
Power-On Sequence State Machine
• Consist of State Diagrams
• Specify expected behavior of the host
and device Phy from power-on to
establishment of an active
communication channel
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SATA Clause 8
Power-On Sequence State Machine
• In states where:
– the Phy relies on detection of received
ALIGNp primitives OR
– comma sequences for state transitions
• Phy shall:
– ensure accurate detection of received
ALIGNp primitives at the compatible
signaling rate (continued on next slide)
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SATA Clause 8
Power-On Sequence State Machine
• Phy shall:
– Have adequate implementation safeguards
to ensure no misdetection of ALIGNp
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