Add picorv32_top module with fewer IO pins

Signed-off-by: Clifford Wolf <clifford@clifford.at>

ice40/picorv32.sh

@@ -2,5 +2,5 @@
 set -ex
 rm -f picorv32.v
 wget https://raw.githubusercontent.com/cliffordwolf/picorv32/master/picorv32.v
-yosys -p 'synth_ice40 -nocarry -json picorv32.json -top picorv32' picorv32.v
+yosys -p 'synth_ice40 -nocarry -json picorv32.json -top top' picorv32.v picorv32_top.v
 ../nextpnr-ice40 --hx8k --asc picorv32.asc --json picorv32.json

ice40/picorv32_top.v

@@ -0,0 +1,31 @@
+module top (
+	input clk, resetn,
+	output trap,
+
+	output        mem_valid,
+	output        mem_instr,
+	input         mem_ready,
+
+	output [31:0] mem_addr,
+	output [31:0] mem_wdata,
+	output [ 3:0] mem_wstrb,
+	input  [31:0] mem_rdata
+);
+    picorv32 #(
+        .ENABLE_COUNTERS(0),
+        .TWO_STAGE_SHIFT(0),
+        .CATCH_MISALIGN(0),
+        .CATCH_ILLINSN(0)
+    ) cpu (
+        .clk      (clk      ),
+        .resetn   (resetn   ),
+        .trap     (trap     ),
+        .mem_valid(mem_valid),
+        .mem_instr(mem_instr),
+        .mem_ready(mem_ready),
+        .mem_addr (mem_addr ),
+        .mem_wdata(mem_wdata),
+        .mem_wstrb(mem_wstrb),
+        .mem_rdata(mem_rdata)
+    );
+endmodule