IBM Intel Xeon E5606 49Y3765 User Manual

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The MbxSend() command is used to acquire control of the PECI mailbox and issue 
information regarding the specific request. The completion code response indicates 
whether or not the originator has acquired a lock on the mailbox, and that completion 
code always specifies the Transaction ID associated with that lock (see 

). 

Once a mailbox has been acquired by an originating agent, future requests to acquire 
that mailbox will be denied with an ‘interface busy’ completion code response.

The lock on a mailbox is not achieved until the last bit of the MbxSend() Read FCS is 
transferred (in other words, it is not committed until the command completes). If the 
host aborts the command at any time prior to that bit transmission, the mailbox lock 
will be lost and it will remain available for any other agent to take control.

For all MbxSend() commands that complete successfully, the passing completion code 
(0x4X) includes a 4-bit Transaction ID (‘X’). That ID is the key to the mailbox and must 
be sent when retrieving response data and releasing the lock by using the MbxGet() 
command. 

The Transaction ID is generated internally by the processor and has no relationship to 
the originator of the request. On Intel® Xeon® processor 5600 series, only a single 
outstanding Transaction ID is supported. Therefore, it is recommended that all devices 
requesting actions or data from the Mailbox complete their requests and release their 
semaphore in a timely manner.

In order to accommodate future designs, software or hardware utilizing the PECI 
mailbox must be capable of supporting Transaction IDs between 0 and 15.

The mailbox associated with a particular Transaction ID is only unlocked / released 
upon successful transmission of the last bit of the Read FCS. If the originator aborts the 
transaction prior to transmission of this bit (presumably due to an FCS failure), the 
semaphore is maintained and the MbxGet() command may be retried.

The mailbox is a shared resource that can result in artificial bandwidth conflicts among 
multiple querying processes that are sharing the same originator interface. The 
interface response time is quick, and with rare exception, back to back MbxSend() and 
MbxGet() commands should result in successful execution of the request and release of 
the mailbox. In order to guarantee timely retrieval of response data and mailbox 
release, the mailbox semaphore has a timeout policy. If the PECI bus has a cumulative 
‘0 time of 1ms since the semaphore was acquired, the semaphore is automatically 

 0x88

Machine Check Banks is currently unavailable (selected core is asleep or unavailable)

 0x89

Invalid Core Select for Machine Check Bank Read

0xFF

Unknown/Invalid Mailbox Request