5.0 Memory Organization
CN8478/CN8474A/CN8472A/CN8471A
5.2 Descriptors
Multichannel Synchronous Communications Controller (MUSYCC™)
5.2.4.5 Message
Descriptor
The Message Descriptor is pointed to by the Message Pointer and the Head
Pointer and is maintained in a variable location in shared memory. A Message
Descriptor includes the following fields:
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•
•
•
Buffer Descriptor (when host writes)
Buffer Status Descriptor (when MUSYCC writes)
Data Buffer Pointer
Next Descriptor Pointer
5.2.4.6 Buffer
Descriptor
The Buffer Descriptor is the first dword of a Message Descriptor after the host
has prepared the data structures in memory. All Buffer Descriptors include the
following fields:
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•
•
•
Owner Indicator Bit (OWNER)
No Poll/Poll Indicator (NP)
End of Buffer Interrupt Enable (EOBI)
Buffer Length (BLEN)
The OWNER bit is a generic term for any descriptor. In a Transmit Buffer
Descriptor it is called MUSYCC; in a Receive Buffer Descriptor it is called host.
The names are different to indicate that the active sense of the owner bit is
different between transmit and receive functions.
In addition to the above list of fields, Transmit Buffer Descriptors also include
the following fields:
•
•
•
•
•
End of Message Indicator (EOM)
Idle Code Selection (IC)
Pad Enable (PADEN)
Pad Count (PADCNT)
Repeat Packet Enable (REPEAT)
IC, PADEN, PADCNT, and REPEAT are valid only when EOM = 1.
5-32
Conexant
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CONEXANT [ CONEXANT SYSTEMS, INC ]
