Expander XL state machine question
Elliott, Robert (Server Storage)
elliott at hp.com
Thu Feb 24 11:21:04 PST 2005
* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <elliott at hp.com>
An expander is expected to insert ALIGNs on underflows (see section 7.3
on "clock skew management") during a connection. It doesn't care about
the type of connection or what is going on in the connection.
Rob Elliott, elliott at hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology
> -----Original Message-----
> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf
> Of Fred Dutton
> Sent: Thursday, February 24, 2005 12:09 PM
> To: t10 at t10.org
> Subject: Expander XL state machine question
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Fred Dutton <fred.dutton at qlogic.com>
> While in the XL7:Connected state, an expander PHY is required
> to send Transmit Dword messages to the XL
> transmitter to transmit all dwords received with Forward
> Dword indications.
> What type of message should be sent to the XL transmitter
> when there are no Forward Dword indications?
> This can occur because devices may run at slightly different
> clock rates. So if an expander is running
> faster than an end device or any other device connected to
> it, it will, every now and then, end up with a
> "dword bubble" in the transfer and, hence, no Forward Dword
> If the XL state machine sends Transmit Idle Dword messages
> you run the risk of inserting an idle dword in
> the middle of a data frame currently being forwarded.
> I see two options:
> 1) always transmit ALIGN primitives when there are no Forward
> Dword indications, or
> 2) if a data frame is currently being forwarded, transmit
> ALIGN primitives when there are no Forward Dword
> indications, otherwise transmit idle dwords.
> The second option would obviously require the expander to
> have the intelligence to know that data frames
> are being forwarded.
> Are there any potential drawbacks with either option?
> Fred Dutton
> Fred Dutton * QLogic * 949.389.6340
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