Data Transmission Procedure by Burst Structure

The bandwidth of the Interlaken interface is divided into data bursts from the supported
channels. Data packets are transferred across the interface by means of one or more
bursts, with the bursts delineated by means of one or more Control Words.

For the purpose of segmenting a packet of arbitrary size into bursts, the following two
parameters are defined:

(i) BurstMax: The maximum size of a data burst (a multiple of 64 bytes)
(ii) BurstShort: The minimum size of a data burst (a minimum of 32 bytes, with
8-byte increments)

The interface typically operates by sending a burst of data of BurstMax length, followed by
a Control Word. The scheduling logic in the transmitting device is free to choose the order in
which channels are serviced, subject to the constraint of the flow control state. Bursts are
transmitted on each channel until the packet is completely transferred, at which point a new
packet transfer on that channel may begin.

Because the interface is channelized, end-of-packet may occur back-to-back on several
channels with a very small amount of remaining data on each channel. As both transmitter
and receiver memories may be ideally designed with a wide datapath, they would need to
be clocked at very high rates to handle this scenario. To reduce this burden on the receiver
and transmitter, the BurstShort parameter guarantees a minimum separation between
successive Burst Control Words. The minimum BurstShort interval is 32 bytes, with larger
values possible in increments of 8 bytes.

Figure 1 illustrates the minimum separation guaranteed by BurstShort. BurstShort is
enforced by adding extra Idle Control Words before the next Burst Control Word. In the
example below, the EOP_Format for Idle Control Word 1 indicates EOP and the appropriate
size for the Last Data Word, and the CRC24 of Idle Control Word 1 covers both the Last
Data Word and Idle Control Word 1. Idle Control Word 2 and Idle Control Word 3 are
inserted to maintain BurstShort, and the following Burst Control Word pertains to the data
sent after it.

Figure 1 BurstShort Guarantee Illustration

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