From ec152d814af82524cf68df95d7f06b9b70c0d0d0 Mon Sep 17 00:00:00 2001
From: Alejandro Soto <alejandro@34project.org>
Date: Sat, 15 Oct 2022 19:31:55 -0600
Subject: Rework bus architecture

---
 rtl/core/mmu/mmu.sv | 64 ++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 18 deletions(-)

(limited to 'rtl/core/mmu')

diff --git a/rtl/core/mmu/mmu.sv b/rtl/core/mmu/mmu.sv
index 9d118c1..8d3b909 100644
--- a/rtl/core/mmu/mmu.sv
+++ b/rtl/core/mmu/mmu.sv
@@ -27,18 +27,26 @@ module core_mmu
 		DATA
 	} master, next_master;
 
+	logic active, hold_start, hold_write, hold_issue, hold_free, transition;
+	ptr hold_addr;
+	word hold_data_wr;
+
 	//TODO
 	assign insn_data_rd = bus_data_rd;
 	assign data_data_rd = bus_data_rd;
 
 	always_comb begin
 		next_master = master;
-		if(bus_ready) begin
-			if(insn_start)
-				next_master = INSN;
-			else if(data_start)
-				next_master = DATA;
-		end
+		if(bus_ready || !active)
+			unique case(master)
+				DATA: next_master = data_start ? DATA : INSN;
+				INSN: next_master = !data_start && !hold_start ? INSN : DATA;
+			endcase
+
+		// Causa UNOPTFLAT en Verilator con assign
+		transition = master != next_master;
+		hold_issue = transition && hold_start;
+		hold_free = transition || !hold_start;
 
 		insn_ready = 0;
 		data_ready = 0;
@@ -51,36 +59,56 @@ module core_mmu
 		unique case(next_master)
 			INSN: begin
 				bus_addr = insn_addr;
+				bus_write = 0;
+				bus_start = insn_start;
 				bus_data_wr = {32{1'bx}};
 			end
 
 			DATA: begin
 				bus_addr = data_addr;
+				bus_write = data_write;
+				bus_start = data_start;
 				bus_data_wr = data_data_wr;
 			end
 		endcase
+
+		if(hold_issue) begin
+			bus_addr = hold_addr;
+			bus_write = hold_write;
+			bus_start = 1;
+			bus_data_wr = hold_data_wr;
+		end
 	end
 
 	always @(posedge clk) begin
 		master <= next_master;
+		active <= bus_start || (active && !bus_ready);
 
-		unique case(next_master)
-			INSN: begin
-				bus_start <= insn_start;
-				bus_write <= 0;
-			end
+		if(hold_free)
+			unique case(next_master)
+				INSN: begin
+					hold_start <= data_start;
+					hold_addr <= data_addr;
+					hold_write <= data_write;
+					hold_data_wr <= data_data_wr;
+				end
 
-			DATA: begin
-				bus_start <= data_start;
-				bus_write <= data_write;
-			end
-		endcase
+				DATA: begin
+					hold_start <= insn_start;
+					hold_addr <= insn_addr;
+					hold_write <= 0;
+				end
+			endcase
 	end
 
 	initial begin
 		master = INSN;
-		bus_start = 0;
-		bus_write = 0;
+		active = 0;
+
+		hold_addr = 30'b0;
+		hold_start = 0;
+		hold_write = 0;
+		hold_data_wr = 0;
 	end
 
 endmodule
-- 
cgit v1.2.3