CN8478 Datasheet, PDF (176/221 Pages) Conexant Systems, Inc – Multichannel Synchronous Communications Controller (MUSYCC)

6.0 Basic Operation
6.4 Protocol Support
CN8478/CN8474A/CN8472A/CN8471A
Multichannel Synchronous Communications Controller (MUSYCC™)
Long Message (LNG)
Short Message (SHT)
In the case of a Long Message (LNG) error, the received HDLC message size is
determined to be greater than the maximum allowed message size (per MAXSEL
in Channel Configuration Descriptor).
Reason:
• Incorrect transmission of HDLC messages from the distant end.
Effects:
• The Interrupt Descriptor in Interrupt Queue is ERROR = LNG, DIR = 0
(if MSKMSG = 0 in Receive Channel Configuration Descriptor).
• DMAC accesses the Next Message Pointer from the current Message
Descriptor.
• Returns ownership of the current Message Descriptor to the host by
writing the Receive Buffer Status Descriptor with ONR = HOST,
ERROR = LNG (if INHRBSD = 0 in Receive Channel Configuration
Descriptor).
• The BLP scans for the opening flag of the next HDLC message.
• Simultaneously, DMAC checks for Message Descriptor ownership before
transferring received data to shared memory.
Channel Level Recovery Actions:
• None required.
In the case of a Short Message (SHT), the total received HDLC message size
(including FCS) is less than the number of FCS bits specified for the receive
channel. In other words, for a channel configured for 16-bit FCS, a minimum of
an 8-bit payload must be received to avoid a short message error. For this
example, three octets must be received—one octet for payload and two for FCS.
Receiving two octets would be considered a short message.
Reasons:
• Bit errors during transmission.
• Incorrect transmission of HDLC messages from the distant end.
Effects:
• The Interrupt Descriptor in Interrupt Queue is ERROR = SHT, DIR = 0 (if
MSKIDLE = 0 in Receive Channel Configuration Descriptor).
• Maintains ownership of current Message Descriptor.
• The BLP resumes scanning for opening flag of the next HDLC message.
• Simultaneously, MUSYCC checks for Message Descriptor ownership
before proceeding with bit-level operations.
Channel Level Recovery Actions:
• None required.
6-42
Conexant
100660E