Why does my single rank DDR5 RDIMM design fail to compile after upgrading to Quartus® Prime Pro Edition Software version 26.1? - Why does my single rank DDR5 RDIMM design fail to compile after upgrading to Quartus® Prime Pro Edition Software version 26.1? Description Starting with Quartus® Prime Pro Edition software version 26.1, the DDR5 DIMM External Memory Interfaces (EMIF) IP explicitly generates two chip select (CS) signals per sub‑channel for DDR5 RDIMMs in the HDL output, even when using single‑rank RDIMMs. This is required because DDR5 RDIMM calibration and RCD operations depend on the presence of both CS signals, regardless of the number of ranks. Enforcing the generation of both CS0 and CS1 ensures that these signals are properly routed from the FPGA to the DIMM connector and prevents cases where CS1 may be left unconnected on the PCB, which could result in initialization or calibration failures. After upgrading to this software version, compilation may fail if the existing top‑level design exposes only one CS pin per sub‑channel. Resolution To resolve this issue, update your top‑level design to expose two CS pins per sub‑channel and connect both signals to the DDR5 DIMM External Memory Interfaces (EMIF) IP in the project. Before: Verilog output wire [0:0] mem_0_cs_n, output wire [0:0] mem_1_cs_n, After: Verilog output wire [1:0] mem_0_cs_n, output wire [1:0] mem_1_cs_n, Custom Fields values: ['novalue'] Troubleshooting QS-9702 novalue ['Memory Controllers'] ['FPGA Dev Tools Quartus® Prime Software Pro'] No plan to fix 26.1 ['Agilex™ 5 FPGAs and SoCs', 'Agilex™ 7 FPGAs and SoCs'] ['novalue'] ['novalue'] ['novalue']