firmware/libcommon/source/iso7816_3.c

/*
 * 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
}