Negotiation On Reselection

ASpaldin at corp.adaptec.com ASpaldin at corp.adaptec.com
Wed Mar 12 09:12:00 PST 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* ASpaldin at corp.adaptec.com
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Header: Adaptec
Text: (34 lines follow)
Thanks to all those who responded  - so far.

Someone pointed out that I didn't really explain why I wanted to know this. 
So here's the reason.

If two SCSI adapters are used for peer-to-peer communication (i.e. both 
operate in Initiator and Target roles) we need to somehow maintain 
negotiation rates properly.

Assumption: only one set of rates per ID (i.e. the same rate is used in both 
directions for Peer to peer - Target and Initiator role agents use same 
rates). 

The following situation can arise:

a) Initiator/Target A receives a READ command from Initiator/Target B 
b) Initiator/Target A sends some data then disconnects (not all of the data 
has been 
    send yet)
c) Initiator/Target A sends a command, e.g. TUR to Initiator/Target B 
d) Initiator/Target B responds with Check Condition

Now Initiator/Target A is ready to send out the remaining data for the READ 
received from Initiator/Target B. As the Check condition might imply 
power/on reset, we need to renegotiate the transfer rates and perform this 
negotiation on the reselection for the READ command.

Does this seem reasonable??

Cheers
alan  

alan spalding
email: alan_spalding at corp.adaptec.com
Original text: (30 lines follow)
>From owner-scsi at Symbios.COM, on 3/12/97 8:59 AM:
To: scsi at Symbios.COM

* From the SCSI Reflector (scsi at symbios.com), posted by:
* ASpaldin at corp.adaptec.com
*
Form: Memo
Text: (17 lines follow)
Does anyone know if Initiators would have a problem with a target which 
renegotiated on a reselection. The SCSI spec do not seem to disallow this.

For example, an Initiator sends the Target a READ command and allows 
disconnection. The Target disconnects at the end of Command phase. At some 
time later the Target reconnects and transfers some data and disconnects. 
The Target then  reconnects (reselection) again to send some more data and 
decides to renegotate( sends WDTR and or SDTR messages after sending the 
Identify message). 

Cheers
alan         

 

alan spalding
email: alan_spalding at corp.adaptec.com
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