diff --git a/firmware/src_simtrace/iso7816_fidi.c b/firmware/src_simtrace/iso7816_fidi.c
new file mode 100644
index 0000000..052654c
--- /dev/null
+++ b/firmware/src_simtrace/iso7816_fidi.c
@@ -0,0 +1,65 @@
+/* ISO7816-3 Fi/Di tables + computation */
+/* (C) 2010-2015 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+
+#include <stdint.h>
+#include <errno.h>
+
+#include "iso7816_fidi.h"
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+/* Table 7 of ISO 7816-3:2006 */
+static const uint16_t fi_table[] = {
+	372, 372, 558, 744, 1116, 1488, 1860, 0,
+	0, 512, 768, 1024, 1536, 2048, 0, 0
+};
+
+/* Table 8 from ISO 7816-3:2006 */
+static const uint8_t di_table[] = {
+	0, 1, 2, 4, 8, 16, 32, 64,
+	12, 20, 2, 4, 8, 16, 32, 64,
+};
+
+/* compute the F/D ratio based on Fi and Di values */
+int compute_fidi_ratio(uint8_t fi, uint8_t di)
+{
+	uint16_t f, d;
+	int ret;
+
+	if (fi >= ARRAY_SIZE(fi_table) ||
+	    di >= ARRAY_SIZE(di_table))
+		return -EINVAL;
+
+	f = fi_table[fi];
+	if (f == 0)
+		return -EINVAL;
+
+	d = di_table[di];
+	if (d == 0)
+		return -EINVAL;
+
+	/* See table 7 of ISO 7816-3: From 1000 on we divide by 1/d,
+	 * which equals a multiplication by d */
+	if (di < 8)
+		ret = f / d;
+	else
+		ret = f * d;
+
+	return ret;
+}