card_emu: Clarify and differentiate F/Fi/F_index/Fi_index

The ISO7816 spec terms are well-defined, let's not abuse them. We used
to consider "Fi" as the "index into the table of F values", while the
spec actually considers Fi as the initial value for F.

Let's make sure we use the terms quite clearly:
* Fi and Di are the initial values for F and D
* F*_index and D*_index are the indexes into the ISO7816-3 Tables

Furthermore, let's track Fi separately from F, as e.g. the waiting
time definition only considers Fi as indicated in the ATR, despite
an actually different F value might have been negotiated via PTS
meanwhile.

Change-Id: Ieb2425e8380a81b79df7b2bd072902994e9c3ee7
Related: OS##1704

1 files changed, 41 insertions, 21 deletions

diff --git a/firmware/libcommon/source/card_emu.c b/firmware/libcommon/source/card_emu.c
index 5feb157..1193121 100644
--- a/firmware/libcommon/source/card_emu.c
+++ b/firmware/libcommon/source/card_emu.c
@@ -1,6 +1,6 @@
 /* ISO7816-3 state machine for the card side
  *
- * (C) 2010-2019 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2010-2021 by Harald Welte <laforge@gnumonks.org>
  * (C) 2018 by sysmocom -s.f.m.c. GmbH, Author: Kevin Redon <kredon@sysmocom.de>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -154,19 +154,35 @@ struct card_handle {
 	bool in_reset;	/*< if card is in reset (true = RST low/asserted, false = RST high/ released) */
 	bool clocked;	/*< if clock is active ( true = active, false = inactive) */
 
-	/* timing parameters, from PTS */
-	uint8_t Fi;
-	uint8_t Di;
+	/* All below variables with _index suffix are indexes from 0..15 into Tables 7 + 8
+	 * of ISO7816-3. */
+
+	/*! Index to clock rate conversion integer Fi (ISO7816-3 Table 7).
+	 *  \note this represents the maximum value supported by the card, and can be indicated in TA1 */
+	uint8_t Fi_index;
+	/*! Current value of index to clock rate conversion integer F (ISO 7816-3 Section 7.1). */
+	uint8_t F_index;
+
+	/*! Index to baud rate adjustment factor Di (ISO7816-3 Table 8).
+	 *  \note this represents the maximum value supported by the card, and can be indicated in TA1 */
+	uint8_t Di_index;
+	/*! Current value of index to baud rate adjustment factor D (ISO 7816-3 Section 7.1). */
+	uint8_t D_index;
+
+	/*! Waiting Integer (ISO7816-3 Section 10.2).
+	 *  \note this value can be set in TA2 */
 	uint8_t wi;
 
+	/*! Waiting Time, in ETU (ISO7816-3 Section 8.1).
+	 *  \note this depends on Fi, Di, and WI if T=0 is used */
+	uint32_t waiting_time;	/* in etu */
+
 	uint8_t tc_chan;	/* TC channel number */
 	uint8_t uart_chan;	/* UART channel */
 
 	uint8_t in_ep;		/* USB IN EP */
 	uint8_t irq_ep;		/* USB IN EP */
 
-	uint32_t waiting_time;	/* in etu */
-
 	/* ATR state machine */
 	struct {
 		uint8_t idx;
@@ -361,16 +377,16 @@ static void emu_update_fidi(struct card_handle *ch)
 {
 	int rc;
 
-	rc = compute_fidi_ratio(ch->Fi, ch->Di);
+	rc = compute_fidi_ratio(ch->F_index, ch->D_index);
 	if (rc > 0 && rc < 0x400) {
-		TRACE_INFO("%u: computed Fi(%u) Di(%u) ratio: %d\r\n",
-			    ch->num, ch->Fi, ch->Di, rc);
+		TRACE_INFO("%u: computed F(%u)/D(%u) ratio: %d\r\n", ch->num,
+			   ch->F_index, ch->D_index, rc);
 		/* make sure UART uses new F/D ratio */
 		card_emu_uart_update_fidi(ch->uart_chan, rc);
 		/* notify ETU timer about this */
 		tc_etu_set_etu(ch->tc_chan, rc);
 	} else
-		TRACE_INFO("%u: computed FiDi ration %d unsupported\r\n",
+		TRACE_INFO("%u: computed F/D ratio %d unsupported\r\n",
 			   ch->num, rc);
 }
 
@@ -395,8 +411,10 @@ static void card_set_state(struct card_handle *ch,
 		break;
 	case ISO_S_WAIT_ATR:
 		/* Reset to initial Fi / Di ratio */
-		ch->Fi = 1;
-		ch->Di = 1;
+		ch->Fi_index = ch->F_index = 1;
+		ch->Di_index = ch->D_index = 1;
+		ch->wi = ISO7816_3_DEFAULT_WI;
+		ch->waiting_time = ISO7816_3_INIT_WTIME;
 		emu_update_fidi(ch);
 		/* the ATR should only be sent 400 to 40k clock cycles after the RESET.
 		 * we use the tc_etu mechanism to wait this time.
@@ -490,7 +508,7 @@ static int tx_byte_atr(struct card_handle *ch)
 			}
 		}
 		/* update waiting time (see ISO 7816-3 10.2) */
-		ch->waiting_time = ch->wi * 960 * ch->Fi;
+		ch->waiting_time = ch->wi * 960 * fi_table[ch->F_index];
 		tc_etu_set_wtime(ch->tc_chan, ch->waiting_time);
 		/* go to next state */
 		card_set_state(ch, ISO_S_WAIT_TPDU);
@@ -626,9 +644,11 @@ static int tx_byte_pts(struct card_handle *ch)
 	case PTS_S_WAIT_RESP_PTS1:
 		byte = ch->pts.resp[_PTS1];
 		/* This must be TA1 */
-		ch->Fi = byte >> 4;
-		ch->Di = byte & 0xf;
-		TRACE_DEBUG("%u: found Fi=%u Di=%u\r\n", ch->num, ch->Fi, ch->Di);
+		ch->F_index = byte >> 4;
+		ch->D_index = byte & 0xf;
+		TRACE_DEBUG("%u: found F=%u D=%u\r\n", ch->num,
+			    fi_table[ch->F_index], di_table[ch->D_index]);
+		/* FIXME: if F or D are 0, become unresponsive to signal error condition */
 		break;
 	case PTS_S_WAIT_RESP_PTS2:
 		byte = ch->pts.resp[_PTS2];
@@ -653,7 +673,7 @@ static int tx_byte_pts(struct card_handle *ch)
 	switch (ch->pts.state) {
 	case PTS_S_WAIT_RESP_PCK:
 		card_emu_uart_wait_tx_idle(ch->uart_chan);
-		/* update baud rate generator with Fi/Di */
+		/* update baud rate generator with F/D */
 		emu_update_fidi(ch);
 		/* Wait for the next TPDU */
 		card_set_state(ch, ISO_S_WAIT_TPDU);
@@ -1024,8 +1044,8 @@ void card_emu_report_status(struct card_handle *ch, bool report_on_irq)
 	if (ch->in_reset)
 		sts->flags |= CEMU_STATUS_F_RESET_ACTIVE;
 	/* FIXME: voltage + card insert */
-	sts->fi = ch->Fi;
-	sts->di = ch->Di;
+	sts->F_index = ch->F_index;
+	sts->D_index = ch->D_index;
 	sts->wi = ch->wi;
 	sts->waiting_time = ch->waiting_time;
 
@@ -1231,8 +1251,8 @@ struct card_handle *card_emu_init(uint8_t slot_num, uint8_t tc_chan, uint8_t uar
 	ch->in_reset = in_reset;
 	ch->clocked = clocked;
 
-	ch->Fi = 0;
-	ch->Di = 1;
+	ch->Fi_index = ch->F_index = 1;
+	ch->Di_index = ch->D_index = 1;
 	ch->wi = ISO7816_3_DEFAULT_WI;
 
 	ch->tc_chan = tc_chan;