22.214.171.124. Example of Loops Limiting the Critical Chain
The following screenshots show the relevant panels from the Fast Forward Details report and the logic contained in the critical chain.
In Figure 117, the Register ID for the start and end points is the same, which is #1. This case indicates that the start and end points of the chain are the same, thereby creating a loop.
Figure 119 shows the output of the Addr_wr register feeding back to its enable input through eight levels of combinational logic.
The figure does not show the other inputs to the logic cone for the Addr_wr register. Source Code for Critical Chain shows portions of the source, and some inputs to the Addr_wr registers.
Source Code for Critical Chain
assign Add_wr_pluse =Add_wr+1; assign Add_wr_pluse_pluse =Add_wr+4; always @ (Add_wr_pluse or Add_rd_ungray) if (Add_wr_pluse==Add_rd_ungray) Full =1; else Full =0; always @ (posedge Clk_SYS or posedge Reset) if (Reset) Add_wr <= 0; else if (Wr_en&&!Full) Add_wr <= Add_wr +1;
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