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Optimized critial path in ifu's spill logic.

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Ross Thompson 2023-07-19 14:13:46 -05:00
parent 97a16f75dc
commit 538efaf771
1 changed files with 6 additions and 3 deletions
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9
src/ifu/spill.sv
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@ -51,7 +51,7 @@ module spill import cvw::*; #(parameter cvw_t P) (
localparam SPILLTHRESHOLD = P.ICACHE_SUPPORTED ? P.ICACHE_LINELENINBITS/32 : 1;
statetype CurrState, NextState;
logic [P.XLEN-1:0] PCPlus2F;
logic [P.XLEN-1:0] PCPlus2NextF, PCPlus2F;
logic TakeSpillF;
logic SpillF;
logic SelSpillF;
@ -63,10 +63,13 @@ module spill import cvw::*; #(parameter cvw_t P) (
////////////////////////////////////////////////////////////////////////////////////////////////////
// compute PCF+2 from the raw PC+4
mux2 #(P.XLEN) pcplus2mux(.d0({PCF[P.XLEN-1:2], 2'b10}), .d1({PCPlus4F, 2'b00}), .s(PCF[1]), .y(PCPlus2F));
mux2 #(P.XLEN) pcplus2mux(.d0({PCF[P.XLEN-1:2], 2'b10}), .d1({PCPlus4F, 2'b00}), .s(PCF[1]), .y(PCPlus2NextF));
// select between PCNextF and PCF+2
mux2 #(P.XLEN) pcnextspillmux(.d0(PCNextF), .d1(PCPlus2F), .s(SelSpillNextF & ~FlushD), .y(PCSpillNextF));
mux2 #(P.XLEN) pcnextspillmux(.d0(PCNextF), .d1(PCPlus2NextF), .s(SelSpillNextF & ~FlushD), .y(PCSpillNextF));
// select between PCF and PCF+2
// not required for functional correctness, but improves critical path. pcspillf ends up on the hptw's ihadr
// and into the dmmu. Cutting the path here removes the PC+4 adder.
flopr #(P.XLEN) pcplus2reg(clk, reset, PCPlus2NextF, PCPlus2F);
mux2 #(P.XLEN) pcspillmux(.d0(PCF), .d1(PCPlus2F), .s(SelSpillF), .y(PCSpillF));
////////////////////////////////////////////////////////////////////////////////////////////////////