fix #97, we need the RF95 IRQ to be level triggered, or we have slim chance of missing events

src/rf95/RH_RF95.cpp

@@ -115,11 +115,11 @@ bool RH_RF95::init()
     }
     _deviceForInterrupt[_myInterruptIndex] = this;
     if (_myInterruptIndex == 0)
-        attachInterrupt(interruptNumber, isr0, RISING);
+        attachInterrupt(interruptNumber, isr0, ONHIGH);
     else if (_myInterruptIndex == 1)
-        attachInterrupt(interruptNumber, isr1, RISING);
+        attachInterrupt(interruptNumber, isr1, ONHIGH);
     else if (_myInterruptIndex == 2)
-        attachInterrupt(interruptNumber, isr2, RISING);
+        attachInterrupt(interruptNumber, isr2, ONHIGH);
     else
         return false; // Too many devices, not enough interrupt vectors
 
@@ -153,6 +153,17 @@ void RH_RF95::handleInterrupt()
     // Read the interrupt register
     uint8_t irq_flags = spiRead(RH_RF95_REG_12_IRQ_FLAGS);
 
+    // ack all interrupts, note - we did this already in the RX_DONE case above, and we don't want to do it twice
+    // Sigh: on some processors, for some unknown reason, doing this only once does not actually
+    // clear the radio's interrupt flag. So we do it twice. Why? (kevinh - I think the root cause we want level
+    // triggered interrupts here - not edge.  Because edge allows us to miss handling secondard interrupts that occurred
+    // while this ISR was running.  Better to instead, configure the interrupts as level triggered and clear pending
+    // at the _beginning_ of the ISR.  If any interrupts occur while handling the ISR, the signal will remain asserted and
+    // our ISR will be reinvoked to handle that case)
+    // kevinh: turn this off until root cause is known, because it can cause missed interrupts!
+    // spiWrite(RH_RF95_REG_12_IRQ_FLAGS, 0xff); // Clear all IRQ flags
+    spiWrite(RH_RF95_REG_12_IRQ_FLAGS, 0xff); // Clear all IRQ flags
+
     // Note: there can be substantial latency between ISR assertion and this function being run, therefore
     // multiple flags might be set.  Handle them all
 
@@ -170,8 +181,6 @@ void RH_RF95::handleInterrupt()
         // in the header. If not it might be a stray (noise) packet.*
         uint8_t crc_present = spiRead(RH_RF95_REG_1C_HOP_CHANNEL) & RH_RF95_RX_PAYLOAD_CRC_IS_ON;
 
-        spiWrite(RH_RF95_REG_12_IRQ_FLAGS, 0xff); // Clear all IRQ flags, required before reading fifo (according to datasheet)
-
         if (!crc_present) {
             _rxBad++;
             clearRxBuf();
@@ -218,15 +227,6 @@ void RH_RF95::handleInterrupt()
         _cad = irq_flags & RH_RF95_CAD_DETECTED;
         setModeIdle();
     }
-
-    // ack all interrupts, note - we did this already in the RX_DONE case above, and we don't want to do it twice
-    if (!(irq_flags & RH_RF95_RX_DONE)) {
-        // Sigh: on some processors, for some unknown reason, doing this only once does not actually
-        // clear the radio's interrupt flag. So we do it twice. Why?
-        // kevinh: turn this off until root cause is known, because it can cause missed interrupts!
-        // spiWrite(RH_RF95_REG_12_IRQ_FLAGS, 0xff); // Clear all IRQ flags
-        spiWrite(RH_RF95_REG_12_IRQ_FLAGS, 0xff); // Clear all IRQ flags
-    }
 }
 
 // These are low level functions that call the interrupt handler for the correct