cx28500 Mindspeed Technologies, cx28500 Datasheet - Page 163

• Manufacturer Part Number: cx28500
• Description: Cx28500 Multichannel Synchronous Communications Controller
• Manufacturer: Mindspeed Technologies

To provide a mechanism for the self-served transmitter to recover from a receiver error, RDMA automatically sets
ABORT ≠ 0 in the buffer descriptor upon detection of any receive error (EOM is also set to one). In HDLC mode,
ABORT ≠ 0 in the buffer descriptor causes the transmitter to send an abort sequence. In Transparent mode,
ABORT ≠ 0 in the buffer descriptor causes pad fill transmission until the next message is available. In either case,
subsequent message transmission remains unaffected.
Two things are important to notice:
1. If the transmitter is slower than the receiver (even by a tiny fraction), it will not empty the buffers fast enough
2. If the receiver marks End Of Message (EOM) in a Buffer Status Descriptor, it also changes the BLEN field to a
28500-DSH-002-C
and the receiver will eventually overflow the internal buffers.
value that is necessarily lower than the original value. The transmitter sends the correct number of bytes and
relinquishes ownership, but it does not return the BLEN to the original value. The receiver, upon wrapping
around and reaching this buffer will see the new (lower) value of BLEN instead of the older (higher) value. Over
a long period of time, this can cause problems as buffers become shorter and shorter. The solution is to use
buffers that are all the same length, and periodically test the Buffer Descriptor Table to return the BLEN fields to
the original value (be careful, though, not to overwrite the BLEN field of a buffer that the transmitter has not yet
begun sending).
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Self-Servicing Buffers
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