I have very weird problem with a library I am creating. The library will be used to communicate between Arduino modules using XBee Series 1 modules. Library is very simple wrapper library around Arduino XBee library.
At one point I need to pass a structure as an argument to one of the functions in the library. This is the function that is responsible for creating a response packet and sending it. I will illustrate the problem using simple example of an "echo service" library - Arduino sends back to a given address the content of the packet that was received.
I want to pass to the function that processes the packet a structure with some data. However, I noticed when I pass the structure, the behavior of other (seemingly non related) parts of code is different. Namely, if I pass as structure to the function as a value, received packet will be read by XBee not correctly. If I pass a structure by a pointer, the behavior is correct. Below there is a simple example that illustrates my problem.
Library:
ExampleLib.h
#ifndef ExampleLib_h
#define ExampleLib_h
#include "Arduino.h"
#include <XBee.h>
#define ADDRESS_BROADCAST 0xffff
#define ADDRESS_PC 0x3333
typedef struct
{
int valA;
int valB;
int valC;
} valuesStruct;
class ExampleLib
{
public:
ExampleLib();
void setSerial(Stream &serial);
boolean tryReceivePacket();
void processPacket();
// THIS FUNCTION IS NOT WORKING!
void processPacket(valuesStruct valuesStructData);
void processPacket(valuesStruct* valuesStructData);
private:
XBee xbee;
Rx16Response rx16;
};
#endif
ExampleLib.cpp
As you cna see here, I have three 'processPacket' functions that differ only by an argument passed - no argument, structure or structure pointer. In case of no argument and structure pointer the behavior of the function is correct, in case of a structure behavior is not correct and I cannot explain it - data read by " rx16.getData()" is not correct.
#include "Arduino.h"
#include <XBee.h>
#include "ExampleLib.h"
ExampleLib::ExampleLib()
{
xbee = XBee();
rx16 = Rx16Response();
}
void ExampleLib::setSerial(Stream &serial)
{
xbee.setSerial(serial);
}
boolean ExampleLib::tryReceivePacket()
{
xbee.readPacket();
if (xbee.getResponse().isAvailable()) {
// got something
if (xbee.getResponse().getApiId() == RX_16_RESPONSE) {
// got a rx packet
xbee.getResponse().getRx16Response(rx16);
return true;
}
else {
return false;
}
}
else if (xbee.getResponse().isError()) {
//nss.print("Error reading packet. Error code: ");
//nss.println(xbee.getResponse().getErrorCode());
// or flash error led
return false;
}
return false;
}
void ExampleLib::processPacket()
{
byte* packetData = rx16.getData();
byte dataLength = rx16.getDataLength();
Serial.print("START L:");
Serial.println(dataLength);
for (int i = 0; i < dataLength; i++) {
Serial.print(packetData[i]);
Serial.print(" - ");
}
Serial.println("END");
//16-bit addressing: Enter address of remote XBee, typically the coordinator
Tx16Request tx = Tx16Request(ADDRESS_PC, packetData, sizeof(packetData));
xbee.send(tx);
}
void ExampleLib::processPacket(valuesStruct valuesStructData)
{
processPacket();
}
void ExampleLib::processPacket(valuesStruct* valuesStructData)
{
processPacket();
}
sketch
#include <XBee.h>
#include <ExampleLib.h>
ExampleLib exampleLibObj = ExampleLib();
void setup()
{
Serial.begin(9600);
exampleLibObj.setSerial(Serial);
}
void loop()
{
boolean isPacketReceived = exampleLibObj.tryReceivePacket();
if (isPacketReceived) {
// leave only one section, the rest should be commented
//Section 1: working
exampleLibObj.processPacket();
//Section 2: not working
// valuesStruct test;
// test.valA = 0;
// test.valB = 0;
// test.valC = 0;
// exampleLibObj.processPacket(test);
//Section 3: working
// valuesStruct* test;
// test->valA = 0;
// test->valB = 0;
// test->valC = 0;
// exampleLibObj.processPacket(test);
}
}
Basically, we trigger the same function, and a behavior differs if we use a structure as an argument (although we never use or call this structure). This is a very mysterious behavior to me. Do you have any idea what can be the problem?
Thanks in advance for any help.
Michal