From 0a791f6d4bfbc755d9ca41ebafe57824ce74329d Mon Sep 17 00:00:00 2001
From: Ralf Edmund Stranzenbach <ralf@reswi.de>
Date: Tue, 14 Oct 2014 23:53:17 +0200
Subject: [PATCH] Receive may freeze if CAN saturated

If either the CANBUS is saturated or the MCU is busy for some time, both RX buffers of the MCP2515 may be in use. If the MCU does not catch up in processing the incoming messages, the second message received just adds another reason for the IRQ.
Thus reading a single message does not clear the IRQ conditon of the MCP2515 leading to a permanent lock up of the receiver program.

Signed-off-by: Ralf Edmund Stranzenbach <ralf@reswi.de>
---
 .../receive_interrupt/receive_interrupt.ino   | 31 ++++++++++++-------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/examples/receive_interrupt/receive_interrupt.ino b/examples/receive_interrupt/receive_interrupt.ino
index 269b4b8..22507b9 100644
--- a/examples/receive_interrupt/receive_interrupt.ino
+++ b/examples/receive_interrupt/receive_interrupt.ino
@@ -41,20 +41,27 @@ void MCP2515_ISR()
 
 void loop()
 {
-    if(Flag_Recv)                   // check if get data
-    {
+  if(Flag_Recv) {                   // check if get data
     
-        Flag_Recv = 0;                // clear flag
-        CAN.readMsgBuf(&len, buf);    // read data,  len: data length, buf: data buf
-
-        for(int i = 0; i<len; i++)    // print the data
-        {
-            Serial.print(buf[i]);Serial.print("\t");
-        }
-        Serial.println();
-    }
+    Flag_Recv = 0;                // clear flag
+    
+    // iterate over all pending messages
+    // If either the bus is saturated or the MCU is busy,
+    // both RX buffers may be in use and reading a single
+    // message does not clear the IRQ conditon.
+    while (CAN_MSGAVAIL == CAN.checkReceive()) {
+      // read data,  len: data length, buf: data buf
+      CAN.readMsgBuf(&len, buf);
+      
+      // print the data
+      for(int i = 0; i<len; i++) {
+	Serial.print(buf[i]);Serial.print("\t");
+      }
+      Serial.println();
+    } 
+  }
 }
 
 /*********************************************************************************************************
   END FILE
-*********************************************************************************************************/
\ No newline at end of file
+*********************************************************************************************************/