Page 105 - Hacking Roomba

86 Part I — Interfacing

Bluetooth adapters on Windows, opening a port will succeed, but trying to write to it
will fail unless enough time has elapsed for the virtual serial port to be initialized. Waiting
for DSR to be true seems to fix this problem. When writing your own code, be sure to
include roombacomm.waitForDSR=true; before connecting because this will trigger the
waitForDSR clause in connect(). In all example programs in this book, the command-line
ones take a -hwhandshake flag, and the GUI ones have a h/w handshake check box to set
waitForDSR to true. It’s called h/w handshake for hardware handshake, which is what the
DSR is part of. Some slower serial port systems or those with very fast data transfer use extra
hardware signals like DSR to indicate when it’s okay to send or receive data. On modern com-
puters this handshaking is rarely needed. For now you can hack around the virtual serial port
initialization problem by waiting for the DSR line. This will probably eventually be updated,
and when it is you’ll be able to simplify your code by removing the waitForDSR clause and
related code.

When using Windows and Bluetooth adapters, use the -hwhandshake flag or select the h/w
handshake check box to make RoombaComm deal with Windows virtual serial ports correctly.

Listing 4-1: Important Methods in RoombaComm and
RoombaCommSerial

private boolean connect(String portid) {
portname = portid;
boolean success = false;
try {
Enumeration portList =
CommPortIdentifier.getPortIdentifiers();
while(portList.hasMoreElements()) {
CommPortIdentifier portId =
(CommPortIdentifier) portList.nextElement();
if(portId.getPortType() == CommPortIdentifier.PORT_SERIAL)
{
if (portId.getName().equals(portname)) {
port = (SerialPort)portId.open(“roomba serial”,2000);
input = port.getInputStream();
output = port.getOutputStream();

port.setSerialPortParams(rate,databits,stopbits,parity);
port.addEventListener(this);
port.notifyOnDataAvailable(true);
logmsg(“port “+portname+” opened successfully”);
if(waitForDSR) {
int i=40;
while( !port.isDSR() && i-- != 0) {
logmsg(“DSR not ready yet”);
pause(150); // 150*40 = 6 seconds
}
success = port.isDSR();
} else {