CN8478 Datasheet, PDF (172/221 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™)
Overflow Due to Internal FIFO
Buffer Overrun (BUFF)
Once a descriptor is granted, however, MUSYCC assumes ownership of the
message buffer and continues writing data until the end of buffer is reached. If the
host reclaims the buffer without MUSYCC granting ownership back to the host, a
host error occurs and the effects are indeterminate.
Reason:
• Degradation of host subsystem or application software performance.
Effects:
• Interrupt Descriptor in Interrupt Queue with ERROR = ONR, DIR = 0
(if MSKBUFF = 0 in Receive Channel Configuration Descriptor).
• The received data in the internal FIFO buffer is discarded and lost to the
host.
• The remainder of the HDLC message currently being received is
discarded.
• The Receive Buffer Status Descriptor cannot be written.
• The channel is deactivated.
Channel Level Recovery Actions:
• Provide sufficient amount of shared memory to store received data using
the lists of Message Descriptors with ownership granted to MUSYCC.
• Reactivate channel.
In the case of overflow due to internal FIFO buffer overrun, the internal FIFO
buffer has not been completely copied to shared memory before more data bits
arrive needing to be stored in the FIFO buffer. MUSYCC has access to a message
buffer space in shared memory in this case.
Reasons:
• Degradation of host sub system performance.
• Congestion of the PCI bus.
Effects:
• The Interrupt Descriptor in Interrupt Queue with ERROR = BUFF,
DIR = 0 (if MSKBUFF = 0 in Receive Channel Configuration Descriptor).
• The received data in the internal FIFO buffer is discarded and lost to the
host.
• The remainder of HDLC message currently being received is discarded.
• Access the Next Message Pointer from the Current Message Descriptor.
• Return ownership of current Message Descriptor by writing the Receive
Buffer Status Descriptor with ONR = HOST, ERROR = BUFF (if
INHRBSD = 0 in Receive Channel Configuration Descriptor).
• 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.
6-38
Conexant
100660E