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Fixed Issue #752 of Verilator simulation by changing LRUMemory to be nonblocking now that Verilator handles this construct properly

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David Harris 2024-06-18 04:40:38 -07:00
parent 4a4bbdfc43
commit 2fc9edff45
1 changed files with 12 additions and 19 deletions
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31
src/cache/cacheLRU.sv vendored
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@ -48,12 +48,12 @@ module cacheLRU
localparam LOGNUMWAYS = $clog2(NUMWAYS); localparam LOGNUMWAYS = $clog2(NUMWAYS);
logic [NUMWAYS-2:0] LRUMemory [NUMSETS-1:0]; logic [NUMWAYS-2:0] LRUMemory [NUMSETS-1:0];
logic [NUMWAYS-2:0] CurrLRU; logic [NUMWAYS-2:0] CurrLRU, NextLRU, ReadLRU, BypassedLRU;
logic [NUMWAYS-2:0] NextLRU;
logic [LOGNUMWAYS-1:0] HitWayEncoded, Way; logic [LOGNUMWAYS-1:0] HitWayEncoded, Way;
logic [NUMWAYS-2:0] WayExpanded; logic [NUMWAYS-2:0] WayExpanded;
logic AllValid; logic AllValid;
logic ForwardLRU;
genvar row; genvar row;
/* verilator lint_off UNOPTFLAT */ /* verilator lint_off UNOPTFLAT */
@ -131,29 +131,22 @@ module cacheLRU
assign Intermediate[node] = CurrLRU[node] ? int1[LOGNUMWAYS-1:0] : int0[LOGNUMWAYS-1:0]; assign Intermediate[node] = CurrLRU[node] ? int1[LOGNUMWAYS-1:0] : int0[LOGNUMWAYS-1:0];
end end
priorityonehot #(NUMWAYS) FirstZeroEncoder(~ValidWay, FirstZero); priorityonehot #(NUMWAYS) FirstZeroEncoder(~ValidWay, FirstZero);
binencoder #(NUMWAYS) FirstZeroWayEncoder(FirstZero, FirstZeroWay); binencoder #(NUMWAYS) FirstZeroWayEncoder(FirstZero, FirstZeroWay);
mux2 #(LOGNUMWAYS) VictimMux(FirstZeroWay, Intermediate[NUMWAYS-2], AllValid, VictimWayEnc); mux2 #(LOGNUMWAYS) VictimMux(FirstZeroWay, Intermediate[NUMWAYS-2], AllValid, VictimWayEnc);
decoder #(LOGNUMWAYS) decoder (VictimWayEnc, VictimWay); decoder #(LOGNUMWAYS) decoder (VictimWayEnc, VictimWay);
// LRU storage must be reset for modelsim to run. However the reset value does not actually matter in practice. // LRU memory must be reset for Questa to run. The reset value does not matter but it is best to be deterministc.
// This is a two port memory. always_ff @(posedge clk)
// Every cycle must read from CacheSetTag and each load/store must write the new LRU.
// note: Verilator lint doesn't like <= for array initialization (https://verilator.org/warn/BLKLOOPINIT?v=5.021)
// Move to = to keep Verilator happy and simulator running fast
always_ff @(posedge clk) begin
if (reset | (InvalidateCache & ~FlushStage)) if (reset | (InvalidateCache & ~FlushStage))
for (int set = 0; set < NUMSETS; set++) LRUMemory[set] = '0; // exclusion-tag: initialize for (int set = 0; set < NUMSETS; set++) LRUMemory[set] <= '0; // exclusion-tag: initialize
else if(CacheEn) begin else if (CacheEn & LRUWriteEn) LRUMemory[PAdr] <= NextLRU;
// Because we are using blocking assignments, change to LRUMemory must occur after LRUMemory is used so we get the proper value
if(LRUWriteEn & (PAdr == CacheSetTag)) CurrLRU = NextLRU;
else CurrLRU = LRUMemory[CacheSetTag];
if(LRUWriteEn) LRUMemory[PAdr] = NextLRU;
end
end
// LRU read path with write forwarding
assign ReadLRU = LRUMemory[CacheSetTag];
assign ForwardLRU = LRUWriteEn & (PAdr == CacheSetTag);
mux2 #(NUMWAYS-1) ReadLRUmux(LRUMemory[CacheSetTag], NextLRU, ForwardLRU, BypassedLRU);
flop #(NUMWAYS-1) CurrLRUReg(clk, BypassedLRU, CurrLRU);
endmodule endmodule