diff --git a/firmware/ice40-riscv/common/mini-printf.c b/firmware/ice40-riscv/common/mini-printf.c
new file mode 100644
index 0000000..53cfe99
--- /dev/null
+++ b/firmware/ice40-riscv/common/mini-printf.c
@@ -0,0 +1,208 @@
+/*
+ * The Minimal snprintf() implementation
+ *
+ * Copyright (c) 2013,2014 Michal Ludvig <michal@logix.cz>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the auhor nor the names of its contributors
+ *       may be used to endorse or promote products derived from this software
+ *       without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * ----
+ *
+ * This is a minimal snprintf() implementation optimised
+ * for embedded systems with a very limited program memory.
+ * mini_snprintf() doesn't support _all_ the formatting
+ * the glibc does but on the other hand is a lot smaller.
+ * Here are some numbers from my STM32 project (.bin file size):
+ *      no snprintf():      10768 bytes
+ *      mini snprintf():    11420 bytes     (+  652 bytes)
+ *      glibc snprintf():   34860 bytes     (+24092 bytes)
+ * Wasting nearly 24kB of memory just for snprintf() on
+ * a chip with 32kB flash is crazy. Use mini_snprintf() instead.
+ *
+ */
+
+#include "mini-printf.h"
+
+static unsigned int
+mini_strlen(const char *s)
+{
+	unsigned int len = 0;
+	while (s[len] != '\0') len++;
+	return len;
+}
+
+static unsigned int
+mini_itoa(int value, unsigned int radix, unsigned int uppercase, unsigned int unsig,
+	 char *buffer, unsigned int zero_pad)
+{
+	char	*pbuffer = buffer;
+	int	negative = 0;
+	unsigned int	i, len;
+
+	/* No support for unusual radixes. */
+	if (radix > 16)
+		return 0;
+
+	if (value < 0 && !unsig) {
+		negative = 1;
+		value = -value;
+	}
+
+	/* This builds the string back to front ... */
+	do {
+		int digit = value % radix;
+		*(pbuffer++) = (digit < 10 ? '0' + digit : (uppercase ? 'A' : 'a') + digit - 10);
+		value /= radix;
+	} while (value > 0);
+
+	for (i = (pbuffer - buffer); i < zero_pad; i++)
+		*(pbuffer++) = '0';
+
+	if (negative)
+		*(pbuffer++) = '-';
+
+	*(pbuffer) = '\0';
+
+	/* ... now we reverse it (could do it recursively but will
+	 * conserve the stack space) */
+	len = (pbuffer - buffer);
+	for (i = 0; i < len / 2; i++) {
+		char j = buffer[i];
+		buffer[i] = buffer[len-i-1];
+		buffer[len-i-1] = j;
+	}
+
+	return len;
+}
+
+struct mini_buff {
+	char *buffer, *pbuffer;
+	unsigned int buffer_len;
+};
+
+static int
+_putc(int ch, struct mini_buff *b)
+{
+	if ((unsigned int)((b->pbuffer - b->buffer) + 1) >= b->buffer_len)
+		return 0;
+	*(b->pbuffer++) = ch;
+	*(b->pbuffer) = '\0';
+	return 1;
+}
+
+static int
+_puts(char *s, unsigned int len, struct mini_buff *b)
+{
+	unsigned int i;
+
+	if (b->buffer_len - (b->pbuffer - b->buffer) - 1 < len)
+		len = b->buffer_len - (b->pbuffer - b->buffer) - 1;
+
+	/* Copy to buffer */
+	for (i = 0; i < len; i++)
+		*(b->pbuffer++) = s[i];
+	*(b->pbuffer) = '\0';
+
+	return len;
+}
+
+int
+mini_vsnprintf(char *buffer, unsigned int buffer_len, const char *fmt, va_list va)
+{
+	struct mini_buff b;
+	char bf[24];
+	char ch;
+
+	b.buffer = buffer;
+	b.pbuffer = buffer;
+	b.buffer_len = buffer_len;
+
+	while ((ch=*(fmt++))) {
+		if ((unsigned int)((b.pbuffer - b.buffer) + 1) >= b.buffer_len)
+			break;
+		if (ch!='%')
+			_putc(ch, &b);
+		else {
+			char zero_pad = 0;
+			char *ptr;
+			unsigned int len;
+
+			ch=*(fmt++);
+
+			/* Zero padding requested */
+			if (ch=='0') {
+				ch=*(fmt++);
+				if (ch == '\0')
+					goto end;
+				if (ch >= '0' && ch <= '9')
+					zero_pad = ch - '0';
+				ch=*(fmt++);
+			}
+
+			switch (ch) {
+				case 0:
+					goto end;
+
+				case 'u':
+				case 'd':
+					len = mini_itoa(va_arg(va, unsigned int), 10, 0, (ch=='u'), bf, zero_pad);
+					_puts(bf, len, &b);
+					break;
+
+				case 'x':
+				case 'X':
+					len = mini_itoa(va_arg(va, unsigned int), 16, (ch=='X'), 1, bf, zero_pad);
+					_puts(bf, len, &b);
+					break;
+
+				case 'c' :
+					_putc((char)(va_arg(va, int)), &b);
+					break;
+
+				case 's' :
+					ptr = va_arg(va, char*);
+					_puts(ptr, mini_strlen(ptr), &b);
+					break;
+
+				default:
+					_putc(ch, &b);
+					break;
+			}
+		}
+	}
+end:
+	return b.pbuffer - b.buffer;
+}
+
+
+int
+mini_snprintf(char* buffer, unsigned int buffer_len, const char *fmt, ...)
+{
+	int ret;
+	va_list va;
+	va_start(va, fmt);
+	ret = mini_vsnprintf(buffer, buffer_len, fmt, va);
+	va_end(va);
+
+	return ret;
+}