Multi-speed Operation with Rate Negotiation - 8.11 English

CPRI LogiCORE IP Product Guide (PG056)

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8.11 English

To permit rate negotiation by the core, set each bit to 1 in the speed capability register for each permitted speed on the link. For example, to negotiate between 2,457.6 Mb/s and 1,228.8 Mb/s, set the speed capability register to 000 0000 0000 0110. In this case, the core attempts to connect at its highest available rate (2,457.6 Mb/s) for the time designated in the CPRI specification, and then attempts to connect at 1,228.8 Mb/s. If the core is unsuccessful at this rate, it attempts 2,457.6 Mb/s again, and so on.

IMPORTANT: If the speed capability register is reprogrammed during operation so that the current line rate is not set to 1 (indicating the current speed is not a permitted speed), the management block attempts a speed switch to the new highest available rate. This allows the management processor to force a switch to a different line rate, possibly in reaction to capability information exchanged on the C&M channel after bringing the link up.