Visible to Intel only — GUID: vbi1488565819099
Ixiasoft
Visible to Intel only — GUID: vbi1488565819099
Ixiasoft
52.3.4.1. GMII to MII Mode Transition
The elastic buffer works when both write and read ports are having an equal or similar clock frequency. Ethernet operation allows dynamic speed mode changes. During a GMII to MII or MII to GMII mode transition, there could be a possibility that the transmit clock from HPS clock source and PCS block are out of sync in terms of clock frequency. If they are out of sync this causes an overflow/underflow condition to occur.
For example, during GMII to MII mode transition, the transmit clock from the PCS could be running at 25/2.5 MHz while clock switching in HPS may yet to be completed and running at 125 MHz. Clock switching in the PCS and HPS could incur a short period of an inactive clock as well due to graceful clock mux implementation. This challenge is handled through software.A register bit which act as a soft reset to the buffer is defined in this adapter core. Software is responsible to ensure the buffer is disabled when there is a change in the speed configuration of the PCS and MAC. The buffer is enabled only when configuration in both PCS and MAC blocks are completed and a valid transmit clock is running at both read and write ports of the buffer.