Improved icestorm example

scripts/icestorm/Makefile

@@ -1,15 +1,16 @@
 
 TOOLCHAIN_PREFIX = riscv64-unknown-elf-
-ICECUBE_DIR = /opt/lscc/iCEcube2.2014.08
 
 all: example.bin
 
 firmware.elf: firmware.S firmware.c firmware.lds
 	$(TOOLCHAIN_PREFIX)gcc -Os -m32 -ffreestanding -nostdlib -o firmware.elf firmware.S firmware.c \
 			--std=gnu99 -Wl,-Bstatic,-T,firmware.lds,-Map,firmware.map,--strip-debug -lgcc
+	chmod -x firmware.elf
 
 firmware.bin: firmware.elf
 	$(TOOLCHAIN_PREFIX)objcopy -O binary firmware.elf firmware.bin
+	chmod -x firmware.bin
 
 firmware.hex: firmware.bin
 	python3 ../../firmware/makehex.py firmware.bin 128 > firmware.hex
@@ -24,7 +25,7 @@ example.bin: example.txt
 	icepack example.txt example.bin
 
 example_tb.exe: example_tb.v example.v firmware.hex
-	iverilog -o example_tb.exe -s testbench example.v example_tb.v ../../picorv32.v # $(ICECUBE_DIR)/verilog/sb_ice_syn.v
+	iverilog -o example_tb.exe -s testbench example.v example_tb.v ../../picorv32.v
 	chmod -x example_tb.exe
 
 sim: example_tb.exe

scripts/icestorm/example.pcf

@@ -6,4 +6,9 @@ set_io LED4 C5
 set_io LED5 C4
 set_io LED6 B3
 set_io LED7 C3
+
+# on-board oscillator (12.0 MHz)
 set_io clk_pin J3
+
+# external clock on PIO1_01 (pin 4 on 40 pin header)
+#set_io clk_pin R15

scripts/icestorm/example.v

@@ -7,18 +7,8 @@ module top (
 	// -------------------------------
 	// Clock Buffer
 
-	wire clk;
+	wire clk = clk_pin;
 
-`ifdef USE_SB_GB_IO
-	SB_GB_IO #(
-		.PIN_TYPE(6'b 0000_01)
-	) clk_gb (
-		.PACKAGE_PIN(clk_pin),
-		.GLOBAL_BUFFER_OUTPUT(clk)
-	);
-`else
-	assign clk = clk_pin;
-`endif
 
 	// -------------------------------
 	// Reset Generator
@@ -31,6 +21,7 @@ module top (
 			resetn_counter <= resetn_counter + 1;
 	end
 
+
 	// -------------------------------
 	// PicoRV32 Core
 
@@ -60,6 +51,7 @@ module top (
 		.mem_rdata(mem_rdata)
 	);
 
+
 	// -------------------------------
 	// Memory/IO Interface