cx28560 Mindspeed Technologies, cx28560 Datasheet - Page 231

• Manufacturer Part Number: cx28560
• Description: Hdlc Controller
• Manufacturer: Mindspeed Technologies

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28560-DSH-001-B
Overview
Appendix C: Flow Conductor
The Flow Conductor interface provides the system with the information required to
control the rate of the flow of data to the transmit buffer controller. This is necessary
because the System has no other way to know the amount of data presently in the
CX28560’s buffers—the line bit rate of the channel does not provide this information
because HDLC processing can cause a significant skew from the line rate.
Information is provided to the system in the form of reports of the number of words
sent or removed from the buffer since the last report was sent together with the
relevant channel number. Thus, the system can maintain a set of counters, one per
channel, of the amount of space available in each channel’s internal buffer. The
counters are initialized to the size of the buffer on channel activation, then each report
received from the CX28560 increments the counters, and each fragment sent by the
system to the CX28560 causes the relevant counter to be decremented. The only other
consideration is the storage of a message’s last fragment header (that contains the
message command bits). This header is stored in 2 bytes in the channel’s buffer
according to
Figure
Mindspeed Technologies™
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Advance Information
Interface
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