Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 4/01/2024
Public

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12.2.6.9. Address Gap Glue Logic

When interleaving traffic to multiple SDRAMs, the CCU/NCore and MPFE cause regions in the local address map for a given channel to be unused because traffic in that region is directed towards one of the other channels. This creates “gaps” that if not properly accounted for when configuring the SDRAM controller, causes DRAM space to be wasted. The address gap glue logic resolves this issue by “compressing” the local address bus by removing the address bit(s) that remain constant on a given channel. By introducing this glue logic, a contiguously utilized address range is created. The user only needs to consider this contiguous address range when configuring the controller.

As previously discussed, when the CCU/NCore interleaves SDRAM bound traffic between CCU_DMI0 and CCU_DMI1 it does not modify the address and thus creates 4K gaps in the port address map. Traffic from FPGA-to-SDRAM must be similarly interleaved, including the introduction of gaps, to enable the interconnect to behave in a consistent manner regardless of the source of the transaction.

When interleaving is utilized, either A[12] or A[13:12] (depending on mode) is handled by the address gap glue logic.

For the 1x16-bit or 1x32-bit modes the glue logic does not modify the address. Therefore the SDRAM AxADDR[38:0] is equal to the MPFE NoC AxADDR[38:0].

For the 2x16-bit or 2x32-bit modes the AxADDR[38:0] received from the MPFE NoC target NIU is modified to remove AxADDR[12] and shift AxADDR[38:13] down to AxADDR[37:12] such that the address sent to the SDRAM controller is the AxADDR[38:13,11:0] received from the MPFE NoC.

For the 4x16-bit mode the AxADDR[38:0] received from the MPFE NoC target NIU is modified to remove AxADDR[13:12] and shift AxADDR[38:14] down to AxADDR[36:12] such that the address sent to the SDRAM controller is the AxADDR[38:14,11:0] received from the MPFE NoC.

Note: The Fabric Bypass does not go through the Address Gap Glue Logic.