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Fix tool issues with automatic variables in PLRU tree #205

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merged 1 commit into from
Dec 14, 2023
Merged

Fix tool issues with automatic variables in PLRU tree #205

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33 changes: 21 additions & 12 deletions src/plru_tree.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,11 @@ module plru_tree #(
logic [2*(ENTRIES-1)-1:0] plru_tree_q, plru_tree_d;

always_comb begin : plru_replacement
automatic int unsigned idx_base, shift;
automatic logic new_index;
idx_base = 0;
shift = 0;
new_index = 1'b0;
plru_tree_d = plru_tree_q;
// The PLRU-tree indexing:
// lvl0 0
Expand All @@ -53,7 +58,6 @@ module plru_tree #(
// default: begin /* No hit */ end
// endcase
for (int unsigned i = 0; i < ENTRIES; i++) begin
automatic int unsigned idx_base, shift, new_index;
// we got a hit so update the pointer as it was least recently used
if (used_i[i]) begin
// Set the nodes to the values we would expect
Expand All @@ -62,11 +66,20 @@ module plru_tree #(
// lvl0 <=> MSB, lvl1 <=> MSB-1, ...
shift = LogEntries - lvl;
// to circumvent the 32 bit integer arithmetic assignment
new_index = ~((i >> (shift-1)) & 1);
plru_tree_d[idx_base + (i >> shift)] = new_index[0];
new_index = 1'(~(i >> (shift-1)));
plru_tree_d[idx_base + (i >> shift)] = new_index;
end
end
end
end

always_comb begin : plru_output
automatic int unsigned idx_base, shift;
automatic logic new_index;
idx_base = 0;
shift = 0;
new_index = 1'b0;
plru_o = '1;
// Decode tree to write enable signals
// Next for-loop basically creates the following logic for e.g. an 8 entry
// TLB (note: pseudo-code obviously):
Expand All @@ -82,22 +95,18 @@ module plru_tree #(
// the corresponding bit of the entry's index, this is
// the next entry to replace.
for (int unsigned i = 0; i < ENTRIES; i += 1) begin
automatic logic en;
automatic int unsigned idx_base, shift, new_index;
en = 1'b1;
for (int unsigned lvl = 0; lvl < LogEntries; lvl++) begin
idx_base = $unsigned((2**lvl)-1);
// lvl0 <=> MSB, lvl1 <=> MSB-1, ...
shift = LogEntries - lvl;
// en &= plru_tree_q[idx_base + (i>>shift)] == ((i >> (shift-1)) & 1'b1);
new_index = (i >> (shift-1)) & 1;
if (new_index[0]) begin
en &= plru_tree_q[idx_base + (i>>shift)];
// plru_o[i] &= plru_tree_q[idx_base + (i>>shift)] == ((i >> (shift-1)) & 1'b1);
new_index = 1'(i >> (shift-1));
if (new_index) begin
plru_o[i] &= plru_tree_q[idx_base + (i>>shift)];
end else begin
en &= ~plru_tree_q[idx_base + (i>>shift)];
plru_o[i] &= ~plru_tree_q[idx_base + (i>>shift)];
end
end
plru_o[i] = en;
end
end

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