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card_emu: Fix USART timer, particularly in re-start situations

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The existing code started the timer once (and expired once) but didn't
properly handle re-starting of the timer.  Neither did it handle
the 'half time expiration' case.  If we want to call a function after
half the WT expiring, we must of course program the hardware for half
the timeout, and not the full timeout...

Change-Id: Ia999d97f835c27597fcd1cf7ac78bac0ab9c98c1
This commit is contained in:
Harald Welte
2021-04-06 01:25:24 +02:00
parent 2619862fba
commit f83c69ff69
1 changed files with 40 additions and 12 deletions
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52
firmware/libcommon/source/mode_cardemu.c
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@@ -212,6 +212,23 @@ int card_emu_uart_tx(uint8_t uart_chan, uint8_t byte)
return 1;
}
static uint16_t compute_next_timeout(struct cardem_inst *ci)
{
uint32_t want_to_expire;
if (ci->wt.total == 0)
return 0;
if (!ci->wt.half_time_notified) {
/* we need to make sure to expire after half the total waiting time */
OSMO_ASSERT(ci->wt.remaining > (ci->wt.total / 2));
want_to_expire = ci->wt.remaining - (ci->wt.total / 2);
} else
want_to_expire = ci->wt.remaining;
TRACE_INFO("want_to_expire=%u (total=%u, remaining=%u)\r\n", want_to_expire, ci->wt.total, ci->wt.remaining);
/* if value exceeds the USART TO range, use the maximum possible value for one round */
return OSMO_MIN(want_to_expire, 0xffff);
}
/*! common handler if interrupt was received.
* \param[in] inst_num Instance number, range 0..1 (some boards only '0' permitted) */
@@ -254,6 +271,9 @@ static void usart_irq_rx(uint8_t inst_num)
* how many etu have expired since we last sent a byte. See section
* 33.7.3.11 "Receiver Time-out" of the SAM3S8 Data Sheet */
if (csr & US_CSR_TIMEOUT) {
/* clear timeout flag (and stop timeout until next character is received) */
usart->US_CR |= US_CR_STTTO;
/* RX has been inactive for some time */
if (ci->wt.remaining <= (usart->US_RTOR & 0xffff)) {
/* waiting time is over; will stop the timer */
@@ -266,17 +286,26 @@ static void usart_irq_rx(uint8_t inst_num)
if (ci->wt.remaining == 0) {
/* let the FSM know that WT has expired */
card_emu_wtime_expired(ci->ch);
} else if (ci->wt.remaining <= ci->wt.total / 2 && !ci->wt.half_time_notified) {
/* let the FS know that half of the WT has expired */
card_emu_wtime_half_expired(ci->ch);
ci->wt.half_time_notified = true;
/* don't automatically re-start in this case */
} else {
bool half_time_just_reached = false;
if (ci->wt.remaining <= ci->wt.total / 2 && !ci->wt.half_time_notified) {
ci->wt.half_time_notified = true;
/* don't immediately call card_emu_wtime_half_expired(), as that
* in turn may calls card_emu_uart_update_wt() which will change
* the timeout but would be overridden 4 lines below */
half_time_just_reached = true;
}
/* update the counter no matter if we reached half time or not */
usart->US_RTOR = compute_next_timeout(ci);
/* restart the counter (if wt is 0, the timeout is not started) */
usart->US_CR |= US_CR_RETTO;
if (half_time_just_reached)
card_emu_wtime_half_expired(ci->ch);
}
/* if value exceeds the USART TO range, use the maximum for now */
usart->US_RTOR = OSMO_MIN(ci->wt.remaining, 0xffff);
/* clear timeout flag (and stop timeout until next character is received) */
usart->US_CR |= US_CR_STTTO;
/* restart the counter (it wt is 0, the timeout is not started) */
usart->US_CR |= US_CR_RETTO;
}
}
@@ -336,8 +365,7 @@ void card_emu_uart_reset_wt(uint8_t uart_chan)
/* FIXME: guard against race with interrupt handler */
ci->wt.remaining = ci->wt.total;
ci->wt.half_time_notified = false;
/* if value exceeds the USART TO range, use the maximum for now */
usart->US_RTOR = OSMO_MIN(ci->wt.remaining, 0xffff);
usart->US_RTOR = compute_next_timeout(ci);
/* restart the counter (if wt is 0, the timeout is not started) */
usart->US_CR |= US_CR_RETTO;
}