diff --git a/sysmoOCTSIM/gcc/Makefile b/sysmoOCTSIM/gcc/Makefile
index 5d21cb0..cf0484c 100644
--- a/sysmoOCTSIM/gcc/Makefile
+++ b/sysmoOCTSIM/gcc/Makefile
@@ -83,6 +83,7 @@
 octsim_i2c.o \
 ncn8025.o \
 command.o \
+iso7816_3.o \
 hpl/osc32kctrl/hpl_osc32kctrl.o \
 driver_init.o \
 hal/src/hal_usart_async.o \
@@ -132,6 +133,7 @@
 "octsim_i2c.o" \
 "ncn8025.o" \
 "command.o" \
+"iso7816_3.o" \
 "hpl/osc32kctrl/hpl_osc32kctrl.o" \
 "driver_init.o" \
 "hal/src/hal_usart_async.o" \
@@ -188,7 +190,8 @@
 "octsim_i2c.d" \
 "ncn8025.d" \
 "command.d" \
-"hal/src/hal_cache.d" \
+"iso7816_3.d" \
+"hal/src/halcache.d" \
 "hal/src/hal_sleep.d" \
 "hal/utils/src/utils_ringbuffer.d" \
 "hpl/sercom/hpl_sercom.d" \
diff --git a/sysmoOCTSIM/iso7816_3.c b/sysmoOCTSIM/iso7816_3.c
new file mode 100644
index 0000000..f7262fb
--- /dev/null
+++ b/sysmoOCTSIM/iso7816_3.c
@@ -0,0 +1,123 @@
+/*
+ * 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"
+
+const uint16_t iso7816_3_fi_table[16] = {
+	372, 372, 558, 744, 1116, 1488, 1860, 0,
+	0, 512, 768, 1024, 1536, 2048, 0, 0
+};
+
+const uint32_t iso7816_3_fmax_table[16] = {
+	4000000, 5000000, 6000000, 8000000, 12000000, 16000000, 20000000, 0,
+	0, 5000000, 7500000, 10000000, 15000000, 20000000, 0, 0
+};
+
+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)
+ */
+
+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);
+}
+
+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)
+ */
+
+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;
+	}
+
+	return wi * 960UL * (fi/f) * (di/d); // calculate timeout value in ETU
+}
diff --git a/sysmoOCTSIM/iso7816_3.h b/sysmoOCTSIM/iso7816_3.h
new file mode 100644
index 0000000..738d2a2
--- /dev/null
+++ b/sysmoOCTSIM/iso7816_3.h
@@ -0,0 +1,98 @@
+/*
+ * 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
+ *  @implements ISO/IEC 7816-3:2006(E) section 8.1
+ */
+#define ISO7816_3_DEFAULT_FD 372
+/** default baud rate adjustment factor Dd
+ *  @implements ISO/IEC 7816-3:2006(E) section 8.1
+ */
+#define ISO7816_3_DEFAULT_DD 1
+/** default clock rate conversion integer Fi
+ *  @implements 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
+ *  @implements 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
+ *  @implements 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
+ *  @implements 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
+ *  @implements 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
+
+/** Table encoding the clock rate conversion integer Fi
+ *  @note Fi is indicated in TA1, but the same table is used for F and Fn during PPS
+ *  @implements ISO/IEC 7816-3:2006(E) table 7
+ */
+extern const uint16_t iso7816_3_fi_table[];
+
+/** Table encoding the maximum clock frequency f_max in Hz
+ *  @implements 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
+ */
+extern const uint32_t iso7816_3_fmax_table[];
+
+/** Table encoding the baud rate adjust integer Di
+ *  @implements 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
+ */
+extern const uint8_t iso7816_3_di_table[];
+
+/* 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);
+/* 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);
+/** calculate Waiting Time (WT)
+ *  @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)
+ *  @implements 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);