Optimize trap handling

rtl/serv_csr.v

@@ -3,6 +3,7 @@ module serv_csr
   (
    input wire 	    i_clk,
    //State
+   input wire 	    i_init,
    input wire 	    i_en,
    input wire 	    i_cnt0to3,
    input wire 	    i_cnt3,
@@ -11,8 +12,7 @@ module serv_csr
    input wire 	    i_mem_op,
    input wire 	    i_mtip,
    input wire 	    i_trap,
-   input wire 	    i_pending_irq,
-   output wire 	    o_new_irq,
+   output reg 	    o_new_irq,
    //Control
    input wire 	    i_e_op,
    input wire 	    i_ebreak,
@@ -71,15 +71,15 @@ module serv_csr
 
    assign o_csr_in = csr_in;
 
-   assign o_new_irq = !timer_irq_r & timer_irq;
-
-
    always @(posedge i_clk) begin
+      if (!i_init & i_cnt_done) begin
+	 timer_irq_r <= timer_irq;
+	 o_new_irq   <= timer_irq & !timer_irq_r;
+      end
+
       if (i_mie_en & i_cnt7)
 	mie_mtie <= csr_in;
 
-      timer_irq_r <= timer_irq;
-
       /*
        The mie bit in mstatus gets updated under three conditions
 
@@ -124,12 +124,12 @@ module serv_csr
        */
       if (i_mcause_en & i_en & i_cnt0to3 | (i_trap & i_cnt_done)) begin
 	 mcause3_0[3] <= (i_e_op & !i_ebreak) | (!i_trap & csr_in);
-	 mcause3_0[2] <= i_pending_irq | i_mem_op | (!i_trap & mcause3_0[3]);
-	 mcause3_0[1] <= i_pending_irq | i_e_op | (i_mem_op & i_mem_cmd) | (!i_trap & mcause3_0[2]);
-	 mcause3_0[0] <= i_pending_irq | i_e_op | (!i_trap & mcause3_0[1]);
+	 mcause3_0[2] <= o_new_irq | i_mem_op | (!i_trap & mcause3_0[3]);
+	 mcause3_0[1] <= o_new_irq | i_e_op | (i_mem_op & i_mem_cmd) | (!i_trap & mcause3_0[2]);
+	 mcause3_0[0] <= o_new_irq | i_e_op | (!i_trap & mcause3_0[1]);
       end
       if (i_mcause_en & i_cnt_done | i_trap)
-	mcause31 <= i_trap ? i_pending_irq : csr_in;
+	mcause31 <= i_trap ? o_new_irq : csr_in;
    end
 
 endmodule

rtl/serv_state.v

@@ -5,7 +5,6 @@ module serv_state
    input wire 	     i_clk,
    input wire 	     i_rst,
    input wire 	     i_new_irq,
-   output reg 	     o_pending_irq,
    input wire 	     i_dbus_ack,
    output wire 	     o_ibus_cyc,
    input wire 	     i_ibus_ack,
@@ -49,6 +48,7 @@ module serv_state
 
    reg 	stage_two_req;
    reg 	init_done;
+   reg 	misalign_trap_sync;
 
    reg [4:2] o_cnt;
    reg [3:0] o_cnt_r;
@@ -70,7 +70,7 @@ module serv_state
    assign cnt4   = (o_cnt[4:2] == 3'd1) & o_cnt_r[0];
    assign o_cnt7 = (o_cnt[4:2] == 3'd1) & o_cnt_r[3];
 
-   
+
    assign o_alu_shamt_en = o_cnt0to3 | cnt4 | !o_init;
 
    //Take branch for jump or branch instructions (opcode == 1x0xx) if
@@ -86,14 +86,16 @@ module serv_state
 
    assign o_dbus_cyc = !o_cnt_en & init_done & i_mem_op & !i_mem_misalign;
 
-   wire trap_pending = WITH_CSR & ((o_ctrl_jump & i_ctrl_misalign) | (i_mem_op & i_mem_misalign));
-
    //Prepare RF for reads when a new instruction is fetched
    // or when stage one caused an exception (rreq implies a write request too)
-   assign o_rf_rreq = i_ibus_ack | (stage_two_req & trap_pending);
+   assign o_rf_rreq = i_ibus_ack | (stage_two_req & misalign_trap_sync);
 
    //Prepare RF for writes when everything is ready to enter stage two
-   assign o_rf_wreq = ((i_shift_op & (i_alu_sh_done | !i_sh_right) & init_done) | (i_mem_op & i_dbus_ack) | (stage_two_req & (i_slt_op | i_branch_op))) & !trap_pending;
+   // and the first stage didn't cause a misalign exception
+   assign o_rf_wreq = !misalign_trap_sync &
+		      ((i_shift_op & (i_alu_sh_done | !i_sh_right) & init_done) |
+		       (i_mem_op & i_dbus_ack) |
+		       (stage_two_req & (i_slt_op | i_branch_op)));
 
    assign o_rf_rd_en = i_rd_op & o_cnt_en & !o_init;
 
@@ -112,7 +114,7 @@ module serv_state
 
    assign o_ibus_cyc = ibus_cyc & !i_rst;
 
-   assign o_init = two_stage_op & !o_pending_irq & !init_done;
+   assign o_init = two_stage_op & !i_new_irq & !init_done;
 
    always @(posedge i_clk) begin
       //ibus_cyc changes on three conditions.
@@ -170,38 +172,24 @@ module serv_state
       end
    end
 
+   assign o_ctrl_trap = WITH_CSR & (i_e_op | i_new_irq | misalign_trap_sync);
+
    generate
       if (WITH_CSR) begin
-   reg 	irq_sync;
-   reg 	misalign_trap_sync;
-
-   assign o_ctrl_trap = i_e_op | o_pending_irq | misalign_trap_sync;
-
-   always @(posedge i_clk) begin
-      if (i_ibus_ack)
-	irq_sync <= 1'b0;
-      if (i_new_irq)
-	irq_sync <= 1'b1;
-
-      if (i_ibus_ack)
-	o_pending_irq <= irq_sync;
-
-      if (stage_two_req)
-	misalign_trap_sync <= trap_pending;
-      if (o_cnt_done)
-	misalign_trap_sync <= 1'b0;
-      if (i_rst)
-	if (RESET_STRATEGY != "NONE") begin
-	   misalign_trap_sync <= 1'b0;
-	   irq_sync           <= 1'b0;
-	   o_pending_irq      <= 1'b0;
-	end
-
-   end // always @ (posedge i_clk)
-      end else begin
-	 assign o_ctrl_trap = 0;
-	 always @(*)
-	   o_pending_irq = 1'b0;
-      end
+	 //trap_pending is only guaranteed to have correct value during the
+	 // last cycle of the init stage
+	 wire trap_pending = WITH_CSR & ((take_branch & i_ctrl_misalign) |
+					 (i_mem_op    & i_mem_misalign));
+
+	 always @(posedge i_clk) begin
+	    if (o_cnt_done)
+	      misalign_trap_sync <= trap_pending & o_init;
+	    if (i_rst)
+	      if (RESET_STRATEGY != "NONE")
+		misalign_trap_sync <= 1'b0;
+	 end
+      end else
+	always @(*)
+	  misalign_trap_sync = 1'b0;
    endgenerate
 endmodule

rtl/serv_top.v

@@ -149,7 +149,6 @@ module serv_top
    wire 	 rf_csr_out;
 
    wire 	 new_irq;
-   wire 	 pending_irq;
 
    wire [1:0]   lsb;
 
@@ -162,7 +161,6 @@ module serv_top
       .i_rst          (i_rst),
       //State
       .i_new_irq      (new_irq),
-      .o_pending_irq  (pending_irq),
       .i_alu_cmp      (alu_cmp),
       .o_init         (init),
       .o_cnt_en       (cnt_en),
@@ -428,6 +426,7 @@ module serv_top
 	   (
 	    .i_clk        (clk),
 	    //State
+	    .i_init       (init),
 	    .i_en         (cnt_en),
 	    .i_cnt0to3    (cnt0to3),
 	    .i_cnt3       (cnt3),
@@ -436,7 +435,6 @@ module serv_top
 	    .i_mem_op     (mem_op),
 	    .i_mtip       (i_timer_irq),
 	    .i_trap       (trap),
-	    .i_pending_irq (pending_irq),
 	    .o_new_irq    (new_irq),
 	    //Control
 	    .i_e_op       (e_op),