Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
823
Inter-Processor Messaging Unit—Intel
®
81341 and 81342
13.2.1
Door Bell Register Operation
When configuring the Door Bell Register mechanism in the IMU for use, the following
steps are followed:
1. Set bits in DBER associated with the DBSTAT bits that will interrupt the processor.
2. Read DBEOR register to identify DBAR bits which will interrupt the other processor.
When interrupted by an enabled DBSTAT bit, the processor conducts activities
associated with DBSTAT bit, and then clear the DBSTAT bit by writing a ‘1’ to that bit.
When multiple DBSTAT bits are set, the processor may use the Highest Priority Doorbell
bit field of the DBCR to handle the DBSTAT requests in a fixed priority order (see
Section 13.4.1, “Interrupt Prioritization” on page 829
).
The processor may set one or more DBSTAT bits in the other processor by writing to
the DBAR register. The DBAR bits may only be cleared by the other processor.
Figure 118. Door Bell Registers as Viewed by Processor 0 and Processor 1
Door Status Field of DBCR
(Read / Clear)
Door Bell Status Field of DBCR
(Read / Clear)
Door Bell Enable Register
(Read / Write)
Door Bell Enable Register
(Read / Write)
Door Bell Assertion Register
(Read / Set)
Door Bell Assertion Register
(Read / Set)
Door Bell Enable Other Processor Register
(Read Only)
Door Bell Enable Other Processor Register
(Read Only)
Processor 0
Processor 1
Set
Clear
Set
Clear
B6362-01
Note: This diagram depicts each processor’s view of and attributes for the same register. For instance, a given processor’s
DBAR that has Read/Set attributes will be used to set not only the DBAR of the given processor but also the DBSTAT of the
other processor. Likewise, a given processor’s DBSTAT that has Read/Clear attributes will be used to clear not only the
DBSTAT of the given processor but also the DBAR of the other processor. In addition, the DBAR of a given processor will
always read the same as the DBSTAT of the other processor.