1 files changed, 58 insertions, 0 deletions
diff --git a/scripts/icestorm/firmware.c b/scripts/icestorm/firmware.c
new file mode 100644
index 0000000..80a4661
--- /dev/null
+++ b/scripts/icestorm/firmware.c
@@ -0,0 +1,58 @@
+#include <stdint.h>
+
+#ifndef SHIFT_COUNTER_BITS
+#error SHIFT_COUNTER_BITS must be defined as 4 (for simulation) or 18 (for hardware bitstreams)!
+#endif
+
+void output(uint8_t c)
+{
+	*(volatile char*)0x10000000 = c;
+}
+
+uint8_t gray_encode_simple(uint8_t c)
+{
+	return c ^ (c >> 1);
+}
+
+uint8_t gray_encode_bitwise(uint8_t c)
+{
+	unsigned int in_buf = c, out_buf = 0, bit = 1;
+	for (int i = 0; i < 8; i++) {
+		if ((in_buf & 1) ^ ((in_buf >> 1) & 1))
+			out_buf |= bit;
+		in_buf = in_buf >> 1;
+		bit = bit << 1;
+	}
+	return out_buf;
+}
+
+uint8_t gray_decode(uint8_t c)
+{
+	uint8_t t = c >> 1;
+	while (t) {
+		c = c ^ t;
+		t = t >> 1;
+	}
+	return c;
+}
+
+void gray(uint8_t c)
+{
+	uint8_t gray_simple = gray_encode_simple(c);
+	uint8_t gray_bitwise = gray_encode_bitwise(c);
+	uint8_t gray_decoded = gray_decode(gray_simple);
+
+	if (gray_simple != gray_bitwise || gray_decoded != c)
+		while (1) asm volatile ("ebreak");
+
+	output(gray_simple);
+}
+
+void main()
+{
+	for (uint32_t counter = (2+4+32+64) << SHIFT_COUNTER_BITS;; counter++) {
+		asm volatile ("" : : "r"(counter));
+		if ((counter & ~(~0 << SHIFT_COUNTER_BITS)) == 0)
+			gray(counter >> SHIFT_COUNTER_BITS);
+	}
+}