DataAvailable Question

General
1

I first used a serial port in RB 5.5 to read electric submeters. It has always been half-diplex - send a request and process the reply. Now I have been tasked to update the program so they can use a mesh network to read the meters. The mesh provider suggests that the old way will take a long time and that we should change to a full duplex model where we send out a bunch of requests and the replies come back in a random order depending on how many hops in the mesh are needed. The solution I am considering is to use the DataAvailable event to append the buffer to a string property (Responses) of my Connection class . Then a timer would process the data. As part of that process, it would remove the first reply from Responses. I am concerned that Responses could be corrupted if DataAvailable fired while Responses is being shortened.

My thought is to set a Busy property True just before removing the first 102 bytes from Responses, then setting Busy False immediately after. DataAvailable would then say If not Busy then Responses = Responses + me.ReadAll. My concern is that the Busy property might not be changed until the event completes and thus would do nothing.

2

It looks like your replies are all 102 bytes? In that case in the data avalaible event handler I would use lookahead to get the number of bytes available and if > 102 read the first 102 bytes into a reply and add that to an array. The replies would then be discrete and could be processed while receiving more replies

3

I agree with Wayne. In DataAvailable, simply snip off complete messages and append them to an array. In a Timer, process the first message in the array and exit (so you’re not blocking the DataAvailable events). Note that in DataAvailable you can have several different states:

  • an incomplete message
  • a complete message
  • a complete message and a partial message
  • more than one message

You’ll have to code to handle any of the above.

4

This needs more emphasis: SerialConnection.LookAhead

DataAvailable means that data was just appended to the internal buffer. Use LookAhead() to peek at the buffer and Read() to remove bytes from it.

5

Great answers. Thank you all. My first thought was that it would be a nightmare whenever a random extra byte appeared before a good reply. But when that happens, I will be able to determine the start position of the first byte of the message and get the missing bytes from the next item in the array.