Fix flush-stall relationship in porch

3 files changed, 20 insertions, 23 deletions

diff --git a/rtl/core/arm810.sv b/rtl/core/arm810.sv
index ead6f94..083163d 100644
--- a/rtl/core/arm810.sv
+++ b/rtl/core/arm810.sv
@@ -14,7 +14,7 @@ module arm810
 	output word  bus_data_wr
 );
 
-	ptr fetch_insn_pc, insn_addr;
+	ptr fetch_insn_pc, fetch_head, insn_addr;
 	word fetch_insn;
 	logic stall, flush, prefetch_flush, insn_start;
 
diff --git a/rtl/core/fetch/fetch.sv b/rtl/core/fetch/fetch.sv
index dc97909..1853ee0 100644
--- a/rtl/core/fetch/fetch.sv
+++ b/rtl/core/fetch/fetch.sv
@@ -18,10 +18,11 @@ module core_fetch
 	             flush,
 	output word  insn,
 	output ptr   insn_pc,
-	             addr
+	             addr,
+	             fetch_head
 );
 
-	ptr next_pc, head, hold_addr, target;
+	ptr next_pc, hold_addr, target;
 	logic fetched_valid, discard;
 
 	assign flush = branch || prefetch_flush;
@@ -30,20 +31,21 @@ module core_fetch
 
 	core_prefetch #(.ORDER(PREFETCH_ORDER)) prefetch
 	(
+		.head(fetch_head),
 		.fetched(fetched_valid),
 		.*
 	);
 
 	always_comb begin
 		if(branch)
-			head = target;
+			fetch_head = target;
 		else if(prefetch_flush)
-			head = next_pc;
+			fetch_head = next_pc;
 		else
-			head = {30{1'bx}};
+			fetch_head = {30{1'bx}};
 
 		if(flush)
-			addr = head;
+			addr = fetch_head;
 		else if(fetch && fetched_valid)
 			addr = hold_addr + 1;
 		else
diff --git a/rtl/core/porch/porch.sv b/rtl/core/porch/porch.sv
index 2eec438..238da88 100644
--- a/rtl/core/porch/porch.sv
+++ b/rtl/core/porch/porch.sv
@@ -10,6 +10,7 @@ module core_porch
 
 	input  word        fetch_insn,
 	input  ptr         fetch_insn_pc,
+	                   fetch_head,
 	input  insn_decode fetch_dec,
 
 	output word        insn,
@@ -18,16 +19,7 @@ module core_porch
 );
 
 	logic execute, conditional, undefined;
-	insn_decode nop, hold_dec;
-
-	core_porch_conds conds
-	(
-		.*
-	);
-
-	assign nop.ctrl.execute = 0;
-	assign nop.ctrl.undefined = 0;
-	assign nop.ctrl.conditional = 0;
+	insn_decode hold_dec;
 
 	always_comb begin
 		dec = hold_dec;
@@ -36,17 +28,20 @@ module core_porch
 		dec.ctrl.conditional = !flush && (dec.ctrl.conditional || conditional);
 	end
 
+	core_porch_conds conds
+	(
+		.*
+	);
+
 	always_ff @(posedge clk or negedge rst_n)
 		if(!rst_n) begin
 			insn <= `NOP;
 			insn_pc <= 0;
-			hold_dec <= nop;
-		end else if(!stall) begin
-			insn <= fetch_insn;
+			hold_dec <= {$bits(hold_dec){1'b0}};
+		end else if(flush || !stall) begin
+			insn <= flush ? `NOP : fetch_insn;
+			insn_pc <= flush ? fetch_head : fetch_insn_pc;
 			hold_dec <= fetch_dec;
-
-			if(!flush)
-				insn_pc <= fetch_insn_pc;
 		end
 
 endmodule