Re: we are a SAS Core Design team, about SAS protocol, we have some questions, can you help us?

Gerry Houlder gerry.houlder at
Tue Feb 18 06:40:22 PST 2014

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When sending a series of data frames, the target has to wait for an ACK/NAK
balance point before retrying any NAKed frames. In your examples, if the
target has sent frames D0 and D1 and receives a NAK for D0, it must wait
for an ACK or NAK on D1 (balance between frames sent an ACK/ NAKs received)
before a retry of D0 can be attempted.
Once you are retransmitting a data frame, it is best to wait for an ACK on
that frame before resuming transfer of other data frames that have not been
sent yet. If the frame is NAK to many times, the command should be
If D1 got an ACK response, then there is no need to retransmit it after
successful transmission of D0.
On Tue, Feb 18, 2014 at 2:07 AM, Ningzuolin <benber.ning at>wrote:
>  we are a SAS Core Design team, about SAS protocol, we have some
> questions, can you help us?
> Thanks a lot.
> The question is descripted as following
> [image: []]
> Section
> [image: []]
> Question1:Can you explain the highlighted text of SAS specification.
> When target outstanding send two data frame who belong to the same read10
> cmd,initiator response NAK for the first data frame,we don¡¯t know
> target need to wait the second data frame¡¯s ACK/NAK(ACK/NAK
> balanced),before retransmitting the second data frame.
> Because of initiator will response ACK or NAK one by one.When target send
> read data frame outstanding,we thought that target should decide to
> retransmit d0 or not after receiving all outstanding data frames¡¯
> ACK/NAK,otherwise target received ACK/NAK will exceed and couldn¡¯t get
> balanced.We don¡¯t know whether we are right.
> If target don¡¯t need to wait ACK/NAK balanced,can you tell us how the
> initiator process the second data frame.
> For example,one read10 command have two data frame d0 and d1.
> The scenario is described as the followed figures,the relationship of the
> DATA frame and ACK/NAK  we thought is the blue arrow. 	The red arrow
> stand for that arrows poit to frame must be send after received the
> response(ACK/NAK) ate the start of the arrow.The d0(r) stand for retransmit
> d0 data frame.
> Can you help us to point outthis figure is right or wrong?
> Figureg1:
> [image: retransmit1]
> Target send d0 and d1 outstanding .While target received the first NAK,we
> thought it belong to the d0,and retransmit d0(r) and d1(r)
> Question2:received the second NAK target should think it belong to d1 or
> d0(r)?
> Question3:while d0¡¯s response is NAK,whether initiator could don¡¯t
> response NAK/ACK for d1?
> Question4:while retransmit d1,whether need to wait until receiving
> d0(r)¡¯s ACK?
> Question5:when received the first NAK which belong to d0,target will
> retransmit d0 and d1.If received the second response is NAK,which belong to
> d1,whether need to retransmit d0 and d1 again?
> Figure2:
> [image: retransmit2]
> While received the third NAK/ACK,target should think it belong the
> d0(r),and retransmit d0 and d1.
> Question6:Before sending d1(r),whether need to wait receiving d0(r)¡¯s
> response?
> Figure3:
> [image: retransmit4]
> Question7:Before retransmit d1(r),target received d0(r)¡¯s NAK,target
> should retransmit d0 stand for d1?
> [image: retransmit3]
> Question8:If target received d0(r)¡¯s response is ACK,d1(r)¡¯s response
> NAK, target should retransmit d1 only?
> 宁佐林 (Benber)
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