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15397 Discussions

Reducing timing for critical path, Adding pipeline registers not working.

VGovi7
Beginner
213 Views

Hello,

 

I'm trying to optimize a part of my design to meet my timing goal (150 MHz ~6.66ns path) but one register is not being read as a register on my timing analysis and I don't know why. In the timing analyzer it shows the register cell as a logical cell in the middle of the path, however, since it is a register, it should be at the end of the path.

 

My design has 2-stages (i.e. pipelined), at least it is supposed to be but the analyzer is not reading the variable as a register.

 

Here is the code snippet in question:

always_ff @(posedge clk) begin if (rst) begin for (int i = 0; i < 6; i++) read_mux_out_reg[i] <= 0; end else begin for (int i = 0; i < 6; i++) read_mux_out_reg[i] <= read_mux_out[i]; end end

Here is the critical path shown in timing analyzer:

 

timing_register_dfa.png

 

Is there something I need to be doing in the timing analyzer for this to work? Any help is greatly appreciated, I've been stuck on this for a while and I've tried a bunch of things to synthesize a register but none of the I tried change the result of the timing analyzer.

 

Thank you~

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1 Reply
VGovi7
Beginner
164 Views

Well, I figured out my problem. It is because there was a lot of mux concatenation from my arrays to the output (This is because I read combinationaly). I simply added another pipeline stage to compensate and now I am meeting my timing requirements.

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