diff --git a/Makefile b/Makefile
index 897f5cb..b5244ce 100644
--- a/Makefile
+++ b/Makefile
@@ -43,7 +43,7 @@ synth.v: picorv32.v scripts/yosys/synth_sim.ys
 	yosys -qv3 -l synth.log scripts/yosys/synth_sim.ys
 
 firmware/firmware.hex: firmware/firmware.bin firmware/makehex.py
-	python3 firmware/makehex.py $< > $@
+	python3 firmware/makehex.py $< 16384 > $@
 
 firmware/firmware.bin: firmware/firmware.elf
 	$(TOOLCHAIN_PREFIX)objcopy -O binary $< $@
diff --git a/dhrystone/Makefile b/dhrystone/Makefile
index 7e077b1..e799037 100644
--- a/dhrystone/Makefile
+++ b/dhrystone/Makefile
@@ -18,7 +18,7 @@ timing.exe: testbench.v ../picorv32.v
 	chmod -x timing.exe
 
 dhry.hex: dhry.bin ../firmware/makehex.py
-	python3 ../firmware/makehex.py $< > $@
+	python3 ../firmware/makehex.py $< 16384 > $@
 
 dhry.bin: dhry.elf
 	riscv64-unknown-elf-objcopy -O binary $< $@
diff --git a/firmware/makehex.py b/firmware/makehex.py
index 1735d86..70282c2 100644
--- a/firmware/makehex.py
+++ b/firmware/makehex.py
@@ -9,13 +9,16 @@
 
 from sys import argv
 
-with open(argv[1], "rb") as f:
+binfile = argv[1]
+nwords = int(argv[2])
+
+with open(binfile, "rb") as f:
     bindata = f.read()
 
-assert len(bindata) < 60*1024
+assert len(bindata) < 4*nwords
 assert len(bindata) % 4 == 0
 
-for i in range(64*1024//4):
+for i in range(nwords):
     if i < len(bindata) // 4:
         w = bindata[4*i : 4*i+4]
         print("%02x%02x%02x%02x" % (w[3], w[2], w[1], w[0]))
diff --git a/scripts/vivado/Makefile b/scripts/vivado/Makefile
index 3b46bf3..71de1a9 100644
--- a/scripts/vivado/Makefile
+++ b/scripts/vivado/Makefile
@@ -38,9 +38,9 @@ sim_system:
 
 firmware.hex: firmware.S firmware.c firmware.lds
 	$(TOOLCHAIN_PREFIX)gcc -Os -m32 -ffreestanding -nostdlib -o firmware.elf firmware.S firmware.c \
-		 -Wl,-Bstatic,-T,firmware.lds,-Map,firmware.map,--strip-debug -lgcc
+		 --std=gnu99 -Wl,-Bstatic,-T,firmware.lds,-Map,firmware.map,--strip-debug -lgcc
 	$(TOOLCHAIN_PREFIX)objcopy -O binary firmware.elf firmware.bin
-	python3 ../../firmware/makehex.py firmware.bin > firmware.hex
+	python3 ../../firmware/makehex.py firmware.bin 4096 > firmware.hex
 
 tab_%/results.txt:
 	bash tabtest.sh $@
@@ -58,5 +58,5 @@ table.txt:
 clean:
 	rm -rf .Xil/ firmware.bin firmware.elf firmware.hex firmware.map synth_*.log
 	rm -rf synth_*.mmi synth_*.bit synth_system.v table.txt tab_*/ webtalk.jou
-	rm -rf webtalk.log webtalk_*.jou webtalk_*.log xelab.* xsim.* xvlog.*
+	rm -rf webtalk.log webtalk_*.jou webtalk_*.log xelab.* xsim[._]* xvlog.*
 
diff --git a/scripts/vivado/firmware.c b/scripts/vivado/firmware.c
index 95aa8de..6c62169 100644
--- a/scripts/vivado/firmware.c
+++ b/scripts/vivado/firmware.c
@@ -8,7 +8,36 @@ void puts(const char *s)
 	while (*s) putc(*s++);
 }
 
+void *memcpy(void *dest, const void *src, int n)
+{
+	while (n) {
+		n--;
+		((char*)dest)[n] = ((char*)src)[n];
+	}
+	return dest;
+}
+
 void main()
 {
-	puts("Hello World!\n");
+	char message[] = "$Uryyb+Jbeyq!+Vs+lbh+pna+ernq+guvf+zrffntr+gura$gur+CvpbEI32+PCH"
+			"+frrzf+gb+or+jbexvat+whfg+svar.$$++++++++++++++++GRFG+CNFFRQ!$$";
+	for (int i = 0; message[i]; i++)
+		switch (message[i])
+		{
+		case 'a' ... 'm':
+		case 'A' ... 'M':
+			message[i] += 13;
+			break;
+		case 'n' ... 'z':
+		case 'N' ... 'Z':
+			message[i] -= 13;
+			break;
+		case '$':
+			message[i] = '\n';
+			break;
+		case '+':
+			message[i] = ' ';
+			break;
+		}
+	puts(message);
 }