Mario Bambagini / ssWi

A simple wireless protocol to let my examples communicate each other. ssWi stands for Shared Slotted Wireless protocol

Dependents:   rover_car rover_pc supervisor watering_unit ... more

This library aims at implementing a simple communication protocol among nodes, abstracting from the hardware. The name ssWi stands for Shared Slotted Wireless. Wireless is part of the name, even though the library abstracts from the hardware, as the first version was entirely focused on the XBee modules and then the name has not been changed.

The communication channel is represented by ssWiChannel, an abstract class which models the channel that the transceivers access to. The concrete classes must implement the functions: init, read and write. The protocol automatically sends and receives data through the selected channel, exploiting the operting system timers. Addresses are not considered as the communication lays on broadcast transmissions.

The protocol provides the ssWiPort abstraction which is like memory areas shared among all the connected nodes. Reading from one port lets the node retrieve the last written value from the other nodes. Writing on one port means sending such value to other nodes.

Objects instantiated from ssWiSocket are the interface for allowing nodes to access the protocol ports.

/media/uploads/mariob/scheme.png

TODO:

  • improve the parsing of the received messages
  • communication tests with many nodes (so far, only 2 nodes have been tested)

Diff: ssWi.cpp

Revision:
24:80345e511574
Parent:
23:2d57c3ea08dc
--- a/ssWi.cpp	Sun Apr 19 17:59:59 2020 +0000
+++ b/ssWi.cpp	Mon Apr 20 20:27:01 2020 +0000
@@ -1,4 +1,5 @@
 /** \file ssWi.cpp
+ *
  *  \brief implementation of the internal functions for mananing the protocol
  *
  */
@@ -13,23 +14,12 @@
 #include <map>
 
 
-
 /** \brief first byte of the header
  *
- * The header is composed of 3 bytes
+ * The header is composed of 3 bytes: START_0 START_1 START_2
  */
 #define START_0 255
-
-/** \brief second byte of the header
- *
- * The header is composed of 3 bytes
- */
 #define START_1 130
-
-/** \brief third byte of the header
- *
- * The header is composed of 3 bytes
- */
 #define START_2 255
 
 
@@ -41,8 +31,7 @@
 
 /** \brief channel abstraction
  *
- * This object represent the communication channel that can be
- * different means
+ * This object represent the communication channel. It can be different means
  */
 ssWiChannel* channel = NULL;
 
@@ -78,12 +67,12 @@
 {
     if (channel!=NULL)
         return false;
-    //mutexChannel.lock();
+    
+    // nothing else is using the channel
     channel = c;
-    //mutexChannel.unlock();
     TXRate = rateTX > 0 ? 1000/rateTX : 0;
     RXRate = rateRX > 0 ? 1000/rateRX : 0;
-    
+    // start txer and rxer
     readingThread.start(functionReceiver);
     writingThread.start(functionSender);
 
@@ -93,11 +82,15 @@
 void functionSender() {
     static char buffer[INTERNAL_BUFFER_SIZE];
 
-    while (1) {
+    while (true) {
         int n = 3;
         int numFrames = 0;
+        
+        // copy data
         for (std::map<int, ssWiPort>::iterator it = ports.begin();
-            it != ports.end(); it++) {
+                                                      it != ports.end(); it++) {
+            if ((n + sizeof(PortValue) + sizeof(PortID)) > INTERNAL_BUFFER_SIZE)
+                break;
             if ((*it).second.isModified()) {
                 buffer[n++] = (*it).first;
                 PortValue tmp = (*it).second.getTXValue();
@@ -106,15 +99,16 @@
                 numFrames++;
             }
         }
+        // add header and send
         if (numFrames > 0) {
             buffer[0] = START_0;
             buffer[1] = START_1;
             buffer[2] = START_2;
-            if (!mutexChannel.trylock())
-                return;
+            mutexChannel.lock();
             channel->write(buffer, n);
             mutexChannel.unlock();
         }
+        
         thread_sleep_for(TXRate);
     }
 }
@@ -127,16 +121,17 @@
     while(1) {
         thread_sleep_for(RXRate);
 
-        if (!mutexChannel.trylock())
-            return;
+        // read buffer
+        mutexChannel.lock();
         int n = channel->read(buffer + offset);
         mutexChannel.unlock();
-        
+        // not enough to find the header, merge with next message as the buffer 
+        // can contain part of the header
         if (n < 3) {
             offset = n;
             continue;
         }
-
+        // find header
         int index = -1;
         for (int i=0; i<(n-2); i++) {
             if (buffer[i]==START_0 && buffer[i+1]==START_1 && buffer[i+2]==START_2) {
@@ -144,13 +139,11 @@
                 break;
             }
         }
-
-        if (index < 0) {
-            offset = n;
+        // header not found, discard everthing
+        offset = 0;
+        if (index < 0)
             continue;
-        }
-        offset = 0;
-
+        // read samples
         while((index + sizeof(PortID) + sizeof(PortValue)) <= n) {
             PortID port = buffer[index++];
             PortValue value = 0;
@@ -165,15 +158,17 @@
 
 inline bool ssWi_isActive (PortID port)
 {
-    return channel!=NULL && ports.find(port)!=ports.end();
+    return channel != NULL && ports.find(port) != ports.end();
 }
 
 
 bool ssWi_setPort (PortID port)
 {
-    if (channel==NULL)
+    if (channel == NULL)
         return false;
+        
     ports[port];
+    
     return true;
 }
 
@@ -182,6 +177,8 @@
 {
     if (!ssWi_isActive(port))
         return false;
+
     ports.erase(port);
+
     return true;
 }