wt_icache: Fix for speculative accesses to NI address (#536)

Signed-off-by: Marcelo Orenes <movera@princeton.edu> Co-authored-by: Marcelo Orenes <movera@princeton.edu>
openhwgroup · Oct 2, 2020 · 9650890 · 9650890
1 parent 9de0800
commit 9650890
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Showing 3 changed files with 11 additions and 2 deletions.
diff --git a/include/ariane_pkg.sv b/include/ariane_pkg.sv
@@ -669,6 +669,7 @@ package ariane_pkg;
         logic                     req;                    // we request a new word
         logic                     kill_s1;                // kill the current request
         logic                     kill_s2;                // kill the last request
+        logic                     spec;                   // request is speculative
         logic [riscv::VLEN-1:0]   vaddr;                  // 1st cycle: 12 bit index is taken for lookup
     } icache_dreq_i_t;
 

diff --git a/src/cache_subsystem/wt_icache.sv b/src/cache_subsystem/wt_icache.sv
@@ -147,7 +147,8 @@ end else begin : gen_piton_offset
 ///////////////////////////////////////////////////////
 // main control logic
 ///////////////////////////////////////////////////////
-
+  logic addr_ni;
+  assign addr_ni = is_inside_nonidempotent_regions(ArianeCfg, areq_i.fetch_paddr);
   always_comb begin : p_fsm
     // default assignment
     state_d      = state_q;
@@ -226,7 +227,7 @@ end else begin : gen_piton_offset
           // readout speculatively
           cache_rden  = cache_en_q;
 
-          if (areq_i.fetch_valid) begin
+          if (areq_i.fetch_valid && (!dreq_i.spec || !addr_ni) ) begin
             // check if we have to flush
             if (flush_d) begin
               state_d  = IDLE;

diff --git a/src/frontend/frontend.sv b/src/frontend/frontend.sv
@@ -252,6 +252,11 @@ module frontend import ariane_pkg::*; #(
     bht_update_t bht_update;
     btb_update_t btb_update;
 
+    // assert on branch, deassert when resolved
+    logic speculative_q,speculative_d;
+    assign speculative_d = (speculative_q && !resolved_branch_i.valid || |is_branch || |is_return || |is_jalr) && !flush_i;
+    assign icache_dreq_o.spec = speculative_d;
+
     assign bht_update.valid = resolved_branch_i.valid
                                 & (resolved_branch_i.cf_type == ariane_pkg::Branch);
     assign bht_update.pc    = resolved_branch_i.pc;
@@ -328,6 +333,7 @@ module frontend import ariane_pkg::*; #(
       if (!rst_ni) begin
         npc_rst_load_q    <= 1'b1;
         npc_q             <= '0;
+        speculative_q     <= '0;
         icache_data_q     <= '0;
         icache_valid_q    <= 1'b0;
         icache_vaddr_q    <= 'b0;
@@ -337,6 +343,7 @@ module frontend import ariane_pkg::*; #(
       end else begin
         npc_rst_load_q    <= 1'b0;
         npc_q             <= npc_d;
+        speculative_q    <= speculative_d;
         icache_valid_q    <= icache_dreq_i.valid;
         if (icache_dreq_i.valid) begin
           icache_data_q        <= icache_data;