Thermal Specifications
Table 6-13. MbxGet() Response Definition
Response
Meaning
CC: 0x85
CC: 0x86
CC: 0xFF
Failure due to lack of Mailbox lock or invalid Transaction ID
Mailbox interface is unavailable or busy
Unknown/Invalid Mailbox Request
6.3.2.9
Mailbox Usage Definition
Acquiring the Mailbox
6.3.2.9.1
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
Section 6.3.2.9.2).
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.
6.3.2.9.2
Transaction ID
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 E7-8800/4800/2800 Product
Families processors, 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.
6.3.2.9.3
6.3.2.9.4
Releasing the Mailbox
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.
Mailbox Timeouts
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
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