diff --git a/firmware/libcommon/include/iso7816_3.h b/firmware/libcommon/include/iso7816_3.h
new file mode 100644
index 0000000..e6c1b4f
--- /dev/null
+++ b/firmware/libcommon/include/iso7816_3.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2019 sysmocom -s.f.m.c. GmbH, Author: Kevin Redon <kredon@sysmocom.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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+/* this library provides utilities to handle the ISO-7816 part 3 communication aspects (e.g. related
+ * to F and D) */
+
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/*! default clock rate conversion integer Fd.
+ *  ISO/IEC 7816-3:2006(E) section 8.1 */
+#define ISO7816_3_DEFAULT_FD 372
+
+/*! default baud rate adjustment factor Dd.
+ *  ISO/IEC 7816-3:2006(E) section 8.1 */
+#define ISO7816_3_DEFAULT_DD 1
+
+/*! default clock rate conversion integer Fi.
+ *  ISO/IEC 7816-3:2006(E) section 8.3
+ *  \note non-default value is optionally specified in TA1 */
+#define ISO7816_3_DEFAULT_FI 372
+
+/*! default baud rate adjustment factor Di.
+ *  ISO/IEC 7816-3:2006(E) section 8.3
+ *  \note non-default value is optionally specified in TA1 */
+#define ISO7816_3_DEFAULT_DI 1
+
+/*! default maximum clock frequency, in Hz.
+ *  ISO/IEC 7816-3:2006(E) section 8.3
+ *  \note non-default value is optionally specified in TA1 */
+#define ISO7816_3_DEFAULT_FMAX 5000000UL
+
+/*! default Waiting Integer (WI) value for T=0.
+ *  ISO/IEC 7816-3:2006(E) section 10.2
+ *  \note non-default value is optionally specified in TC2 */
+#define ISO7816_3_DEFAULT_WI 10
+
+/*! default Waiting Time (WT) value, in ETU.
+ *  ISO/IEC 7816-3:2006(E) section 8.1
+ *  \note depends on Fi, Di, and WI if protocol T=0 is selected */
+#define ISO7816_3_DEFAULT_WT 9600
+
+extern const uint16_t iso7816_3_fi_table[];
+
+extern const uint32_t iso7816_3_fmax_table[];
+
+extern const uint8_t iso7816_3_di_table[];
+
+bool iso7816_3_valid_f(uint16_t f);
+
+bool iso7816_3_valid_d(uint8_t d);
+
+int32_t iso7816_3_calculate_wt(uint8_t wi, uint16_t fi, uint8_t di, uint16_t f, uint8_t d);
diff --git a/firmware/libcommon/source/iso7816_3.c b/firmware/libcommon/source/iso7816_3.c
new file mode 100644
index 0000000..ccdff68
--- /dev/null
+++ b/firmware/libcommon/source/iso7816_3.c
@@ -0,0 +1,159 @@
+/*
+ * Copyright (C) 2019 sysmocom -s.f.m.c. GmbH, Author: Kevin Redon <kredon@sysmocom.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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+#include <stdint.h>
+#include <stddef.h>
+
+#include "utils.h"
+#include "iso7816_3.h"
+
+/*! Table of clock rate conversion integer F indexed by Fi.
+ *  \note Fi is indicated in TA1, but the same table is used for F and Fn during PPS
+ *  ISO/IEC 7816-3:2006(E) table 7 */
+const uint16_t iso7816_3_fi_table[16] = {
+	372, 372, 558, 744, 1116, 1488, 1860, 0,
+	0, 512, 768, 1024, 1536, 2048, 0, 0
+};
+
+/*! Table of maximum clock frequency f_max in Hz indexed by Fi.
+ *  ISO/IEC 7816-3:2006(E) table 7
+ *  \note f_max is indicated in TA1, but the same table is used for F and Fn during PPS */
+const uint32_t iso7816_3_fmax_table[16] = {
+	4000000, 5000000, 6000000, 8000000, 12000000, 16000000, 20000000, 0,
+	0, 5000000, 7500000, 10000000, 15000000, 20000000, 0, 0
+};
+
+/*! Table encoding the baud rate adjust integer D indexed by Di.
+ *  ISO/IEC 7816-3:2006(E) table 8
+ *  \note Di is indicated in TA1, but the same table is used for D and Dn during PPS */
+const uint8_t iso7816_3_di_table[16] = {
+	0, 1, 2, 4, 8, 16, 32, 64,
+	12, 20, 0, 0, 0, 0, 0, 0,
+};
+
+/* All values are based on the Elementary Time Unit (ETU), defined in ISO/IEC 7816-3 section 7.1
+ * this is the time required to transmit a bit, and is calculated as follows:
+ * 	1 ETU = (F / D) x (1 / f)
+ * where:
+ * - F is the clock rate conversion integer
+ * - D is the baud rate adjustment factor
+ * - f is the clock frequency
+ *
+ * The possible F, f(max), and D values are defined in ISO/IEC 7816-3 table 7 and 8
+ * - the initial value for F (after reset) is Fd = 372
+ * - the initial value for D (after reset) is Dd = 1
+ * - the initial maximum frequency f(max) is 5 MHz
+ *
+ * The card must measure the ETU based on the clock signal provided by the reader
+ * one ETU (e.g. 1 bit) takes F/D clock cycles, which the card must count
+ *
+ * The card can indicate an alternative set of supported values Fi (with corresponding f(max)) and
+ * Di for higher baud rate in TA1 in the ATR (see ISO/IEC 7816-3 section 8.3)
+ *
+ * These values are selected according to ISO/IEC 7816-3 section 6.3.1:
+ * - card in specific mode: they are enforced if TA2 is present (the reader can deactivate the card
+ *   if it does not support these values)
+ * - card in negotiable mode:
+ * -- they can be selected by the reader using the Protocol and Parameters Selection (PPS) procedure
+ * -- the first offered protocol and default values are used when no PPS is started
+ *
+ * PPS is done with Fd and Dd (see ISO/IEC 7816-3 section 9) the reader can propose any F and D
+ * values between from Fd to Fi, and from Dd to Di (Fi and Di are indicated in TA1) the in PPS
+ * agreed values F and D are called Fn and Dn and are applied after a successful exchange,
+ * corresponding to PPS1_Response bit 5
+ *
+ * The F and D values must be provided to the SAM3S USART peripheral (after reset and PPS)
+ */
+
+/*! Verify if the clock rate conversion integer F value is valid.
+ *  \param[in] f F value to be validated
+ *  \return if F value is valid
+ *  \note only values in ISO/IEC 7816-3:2006(E) table 7 are valid */
+bool iso7816_3_valid_f(uint16_t f)
+{
+	if (0 == f) {
+		return false;
+	}
+	uint8_t i = 0;
+	for (i = 0; i < ARRAY_SIZE(iso7816_3_fi_table) && iso7816_3_fi_table[i] != f; i++);
+	return (i < ARRAY_SIZE(iso7816_3_fi_table) && iso7816_3_fi_table[i] == f);
+}
+
+/*! Verify if the baud rate adjustment factor D value is valid.
+ *  \param[in] d D value to be validated
+ *  \return if D value is valid
+ *  \note only values in ISO/IEC 7816-3:2006(E) table 8 are valid */
+bool iso7816_3_valid_d(uint8_t d)
+{
+	if (0 == d) {
+		return false;
+	}
+	uint8_t i = 0;
+	for (i = 0; i < ARRAY_SIZE(iso7816_3_di_table) && iso7816_3_di_table[i] != d; i++);
+	return (i < ARRAY_SIZE(iso7816_3_di_table) && iso7816_3_di_table[i] == d);
+}
+
+/* The ETU is not only used to define the baud rate, but also the Waiting Time (WT) (see ISO/IEC
+ * 7816-3 section 8.1)
+ *
+ * when exceeding WT without card response, the reader flags the card as unresponsive, and resets it
+ * this can be used by the card to indicate errors or unsupported operations if the card requires
+ * more time to respond, it shall send a procedure byte to restart WT WT is calculated as follows
+ * (for T=0, see ISO/IEC 7816-3 section 10.2): WT = WI x 960 x (Fi / f(max)) where
+ * - WI is encoded in TC2 in the ATR (10 if absent)
+ * - WI does not depend on D/Di (used for the ETU)
+ * - after reset WT is 9600 ETU
+ * - WI (e.g. the new WT) is applied when T=0 is used (after 6.3.1), even if Fi is not Fn (this WT
+ *   extension is important to know for the reader so to have the right timeout)
+ */
+
+/*! Calculate Waiting Time (WT) in units of ETU.
+ *  \param[in] wi Waiting Integer
+ *  \param[in] fi clock rate conversion integer Fi value
+ *  \param[in] di baud rate adjustment factor Di value
+ *  \param[in] f clock rate conversion integer F value
+ *  \param[in] d baud rate adjustment factor D value
+ *  \return Waiting Time WT, in ETU, or < 0 on error (see code for return codes)
+ *  \note this should happen after reset and T=0 protocol select (through PPS or implicit)
+ *  ISO/IEC 7816-3:2006(E) section 8.1 and 10.2 */
+int32_t iso7816_3_calculate_wt(uint8_t wi, uint16_t fi, uint8_t di, uint16_t f, uint8_t d)
+{
+	/* sanity checks */
+	if (0 == wi)
+		return -1;
+
+	if (!iso7816_3_valid_f(fi))
+		return -2;
+
+	if (!iso7816_3_valid_d(di))
+		return -3;
+
+	if (!iso7816_3_valid_f(f))
+		return -4;
+
+	if (!iso7816_3_valid_d(d))
+		return -5;
+
+	if (f > fi)
+		return -6;
+
+	if (d > di)
+		return -7;
+
+	/* see 7816-3 Section 10.2 */
+	return wi * 960UL * (fi/f) * (di/d); // calculate timeout value in ETU
+}