So far I have been able to successfully read characters from the serial port and organize them into strings. The reading part isn't a problem, I am currently having no issues with that. Where I am stuck is the issue of a connection dropout. If the device connected to the serial port (a GPS simulator in this case) is turned off or disconnected, my program will halt on the line that waits for a character from the serial port. I am using character = input(1, #1) to read the character but if there is nothing there the program will just stop and wait for character to appear at the buffer.
Initially I thought that setting a timeout when I open the COM port with the option 'OPn' (n is time in ms) which is used in the OPEN COM function would help. This didn't help at all. A workmate told me that in Visual BASIC he would create another program thread which would monitor progress of the read function and determine whether it is taking too long by using timers. I then discovered that I could do this in FB. I set it up so that two threads are running at the same time. One is used for reading characters and operating on them, called Main, and one checks how long each read is taking, called TimeOut.
After each character is read a global variable which holds the time is reset. In the other thread a loop checks every 50ms whether this timer has exceeded 1s. If so an END command is issued to stop the program. For some reason the program doesn't stop. It appears that once the Main thread is waiting for a character in the buffer, the whole program has to stop. If the whole program halts then the TimeOut thread can't check whether 1 second has passed because it stops looping. I can't work out how to fix this, I have investigated mutex's but I can't see how they can help me.
I won't put all my code on here, just the relevant stuff:
Code: Select all
dim thread1 as Any Ptr
dim thread2 as Any Ptr
dim shared startTime as double
declare sub TimeOut(param as Any Ptr)
declare sub Main(param as Any Ptr)
if (Open Com ("COM1:4800,N,8,2,CS0,DS0,OP1000" As #1) = 0) then
print "Serial Connection Successful"
print
else
print "Serial Connection Failed"
sleep
end
end if
thread2 = ThreadCreate(@TimeOut)
thread1 = ThreadCreate(@Main)
threadwait(thread2)
print "END OF PROGRAM"
sleep
end
sub Main(param As Any Ptr)
dim serialInput as string
do
serialInput = ""
do
character = ""
character = input(1, #1)
startTime = timer
if (character <> chr(10)) then serialInput += character
loop until character = chr(10) or character = ""
print serialInput
sleep 10
loop until inkey <> ""
print "FINISHED"
end sub
sub TimeOut(param As Any Ptr)
startTime = timer
print "Thread 2 Started"
do
print "Thread 2 Running..."
sleep 50
loop until timer > startTime + 1.0
print "ERROR"
end
end sub