Hi Peter,
I think you have at-least two issues.
First, the SF uses a handshake to determine that there is another SF on
the other side of the socket. You are probably receiving a 'T' then a '
', then SF is waiting for you to respond. The following code implements
the handshake:
boolean validSF = false;
try {
// Make sure we have a valid Serial Forwarder service
logger.info("Testing SF version");
ByteBuffer buffer = ByteBuffer.allocate(10);
int platform = 1;
byte[] check = new byte[20];
byte[] nonce = new byte[6];
int numRead = 0;
int count = 5;
selector.select(3000);
numRead = channel.read(buffer);
if( numRead < 2 ){
logger.error("No response from Serial
Forwarder");
} else {
buffer.flip();
buffer.get(check, 0, numRead);
if(check[0] == 'X'){
validSF = true;
nonce[0] = 'X';
nonce[1] = ' ';
} else if (check[0] ==
'T' && check[1] >= ' '){
validSF = true;
nonce[0] = 'T';
nonce[1] = '!';
} else {
logger.error("Could not verify
Serial Forwarder");
}
if( validSF == true ){
nonce[2] = (byte) (platform & 0xff);
nonce[3] = (byte) (platform >> 8 & 0xff);
nonce[4] = (byte) (platform >> 16 & 0xff);
nonce[5] = (byte) (platform >> 24 & 0xff);
buffer.flip();
buffer.put(nonce, 0 , 6);
buffer.flip();
channel.write(buffer);
}
}
} catch (IOException e){
logger.error("Exception testing Serial Forwarder:
" + e.getMessage());
}
The second issue is that the SF protocol contains SYNC_BYTEs (0x7e) that
bound messages and ESCAPE_BYTESs (0x7d) to allow escaped SYNC_BYTES in the
message. You need to make sure that messages start with the SYNC byte and
escaped bytes are unescaped before you parse the message. Look at
net.tinyos.packet.packetizer and/or .../tools/src/sf/sfsource.c for more
details.
Regards,
Chuck
At 10:32 AM 3/7/2006, Peter Burke wrote:
Hi all,
I've seen a couple of people post similar questions re connecting
custom apps to SerialForwarder but I've had no luck finding answers as yet,
so here's yet another question on the use of SF.
My understanding of the SerialForwarder is that it can be used to stream
serial data (i.e. TOS messages) to any client sitting on the end of a TCP
connection. I'm writing a simple Java client that initially just connects to
SF, receives message packets and writes them to the console.
The problem I'm having is that I can connect to SF & initially receive data
(just 2 bytes) but then my client just sits there waiting for more data.
>From what I can see from the example apps (Oscope etc) there doesn't appear
to be anything special going on, so I'm at a loss. When I connect to the SF
through Telnet, I just see a 'T' character displayed. I've checked
SFProtocol.java but maybe I'm missing something.
I'd appreciate hearing from anyone else who's tried to hook-up to SF in
their own apps and any suggestions they might have.
I've included a small excerpt of my client code, together with the program
output.
// Output
Attempting to connect to localhost:9001
< CONNECTED TO SERIALFORWARDER >
< READ returned 2 bytes>
public void run(){
// read from the stream
int numBytesReturned =
inputStream.read(packet,numBytesRead,PACKET_SIZE - numBytesRead);
System.err.println("< READ returned " + numBytesReturned + " >");
// continue to read until we reach the end of the stream
while(numBytesReturned != -1){
// update the number of bytes read from the stream
numBytesRead += numBytesReturned;
// if we've read enough bytes to form a packet, decode its contents
if(numBytesRead == PACKET_SIZE){
for(int idx = 0; idx < packet.length; idx++){
System.out.print( Integer.toHexString(packet[idx] &
0xFF) + " " );
}
// reset counter
numBytesRead = 0;
// leave a gap to display the next packet
System.out.println();
}
// read another set of bytes
numBytesReturned = inputStream.read(packet,numBytesRead,PACKET_SIZE
- numBytesRead);
}// end while(!EOS)
}// end run
Thanks in advance.
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