pulseIn fix and pulseInLong()

Fixes #384

avr/cores/tinymodern/wiring_pulse.c

@@ -18,8 +18,6 @@
   Public License along with this library; if not, write to the
   Free Software Foundation, Inc., 59 Temple Place, Suite 330,
   Boston, MA  02111-1307  USA
-
-  $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $
 */
 
 #include "wiring_private.h"
@@ -28,42 +26,68 @@
 /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
  * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
  * to 3 minutes in length, but must be called at least a few dozen microseconds
- * before the start of the pulse. */
+ * before the start of the pulse.
+ *
+ * This function performs better with short pulses in noInterrupt() context
+ */
 unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
 {
-  // cache the port and bit of the pin in order to speed up the
-  // pulse width measuring loop and achieve finer resolution.  calling
-  // digitalRead() instead yields much coarser resolution.
-  uint8_t bit = digitalPinToBitMask(pin);
-  uint8_t port = digitalPinToPort(pin);
-  uint8_t stateMask = (state ? bit : 0);
-  unsigned long width = 0; // keep initialization out of time critical area
+    // cache the port and bit of the pin in order to speed up the
+    // pulse width measuring loop and achieve finer resolution.  calling
+    // digitalRead() instead yields much coarser resolution.
+    uint8_t bit = digitalPinToBitMask(pin);
+    uint8_t port = digitalPinToPort(pin);
+    uint8_t stateMask = (state ? bit : 0);
+
+    // convert the timeout from microseconds to a number of times through
+    // the initial loop; it takes approximately 16 clock cycles per iteration
+    unsigned long maxloops = microsecondsToClockCycles(timeout)/16;
+
+    unsigned long width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops);
+
+    // prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out
+    if (width)
+        return clockCyclesToMicroseconds(width * 16 + 16);
+    else
+        return 0;
+}
 
-  // convert the timeout from microseconds to a number of times through
-  // the initial loop; it takes 16 clock cycles per iteration.
-  unsigned long numloops = 0;
-  unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;
+/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
+ * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
+ * to 3 minutes in length, but must be called at least a few dozen microseconds
+ * before the start of the pulse.
+ *
+ * ATTENTION:
+ * this function relies on micros() so cannot be used in noInterrupt() context
+ */
+unsigned long pulseInLong(uint8_t pin, uint8_t state, unsigned long timeout)
+{
+    // cache the port and bit of the pin in order to speed up the
+    // pulse width measuring loop and achieve finer resolution.  calling
+    // digitalRead() instead yields much coarser resolution.
+    uint8_t bit = digitalPinToBitMask(pin);
+    uint8_t port = digitalPinToPort(pin);
+    uint8_t stateMask = (state ? bit : 0);
 
-  // wait for any previous pulse to end
-  while ((*portInputRegister(port) & bit) == stateMask)
-    if (numloops++ == maxloops)
-      return 0;
+    unsigned long startMicros = micros();
 
-  // wait for the pulse to start
-  while ((*portInputRegister(port) & bit) != stateMask)
-    if (numloops++ == maxloops)
-      return 0;
+    // wait for any previous pulse to end
+    while ((*portInputRegister(port) & bit) == stateMask) {
+        if (micros() - startMicros > timeout)
+            return 0;
+    }
 
-  // wait for the pulse to stop
-  while ((*portInputRegister(port) & bit) == stateMask) {
-    if (numloops++ == maxloops)
-      return 0;
-    width++;
-  }
+    // wait for the pulse to start
+    while ((*portInputRegister(port) & bit) != stateMask) {
+        if (micros() - startMicros > timeout)
+            return 0;
+    }
 
-  // convert the reading to microseconds. The loop has been determined
-  // to be 20 clock cycles long and have about 16 clocks between the edge
-  // and the start of the loop. There will be some error introduced by
-  // the interrupt handlers.
-  return clockCyclesToMicroseconds(width * 21 + 16);
+    unsigned long start = micros();
+    // wait for the pulse to stop
+    while ((*portInputRegister(port) & bit) == stateMask) {
+        if (micros() - startMicros > timeout)
+            return 0;
+    }
+    return micros() - start;
 }