Fix pulseIn (#1072, #1149)

- fix return value on timeout
- add optimistic_yield to allow WiFi/network tasks to run
- use ccount instead of micros (which causes an integer division on every call)

cores/esp8266/core_esp8266_wiring_pulse.c

@@ -1,9 +1,9 @@
-/* 
+/*
   pulse.c - wiring pulseIn implementation for esp8266
 
   Copyright (c) 2015 Hristo Gochkov. All rights reserved.
   This file is part of the esp8266 core for Arduino environment.
- 
+
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
@@ -18,19 +18,38 @@
   License along with this library; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
+#include <limits.h>
 #include "wiring_private.h"
 #include "pins_arduino.h"
 
-unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout) {
-  pinMode(pin, INPUT);
-  uint32_t start = micros();
-  while(digitalRead(pin) == state && (micros() - start) < timeout);
-  while(digitalRead(pin) != state && (micros() - start) < timeout);
-  start = micros();
-  while(digitalRead(pin) == state && (micros() - start) < timeout);
-  return micros() - start;
+
+extern uint32_t xthal_get_ccount();
+
+#define WAIT_FOR_PIN_STATE(state) \
+    while (digitalRead(pin) != (state)) { \
+        if (xthal_get_ccount() - start_cycle_count > timeout_cycles) { \
+            return 0; \
+        } \
+        optimistic_yield(5000); \
+    }
+
+// max timeout is 27 seconds at 160MHz clock and 54 seconds at 80MHz clock
+unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
+{
+    const uint32_t max_timeout_us = clockCyclesToMicroseconds(UINT_MAX);
+    if (timeout > max_timeout_us) {
+        timeout = max_timeout_us;
+    }
+    const uint32_t timeout_cycles = microsecondsToClockCycles(timeout);
+    const uint32_t start_cycle_count = xthal_get_ccount();
+    WAIT_FOR_PIN_STATE(!state);
+    WAIT_FOR_PIN_STATE(state);
+    const uint32_t pulse_start_cycle_count = xthal_get_ccount();
+    WAIT_FOR_PIN_STATE(!state);
+    return clockCyclesToMicroseconds(xthal_get_ccount() - pulse_start_cycle_count);
 }
 
-unsigned long pulseInLong(uint8_t pin, uint8_t state, unsigned long timeout) {
+unsigned long pulseInLong(uint8_t pin, uint8_t state, unsigned long timeout)
+{
     return pulseIn(pin, state, timeout);
 }