Re: GNAT.Serial_Communications

[Chris Moore <zmower@ntlworld.com>]

On 13/04/2011 22:12, tonyg wrote:
>
> Its actually blocking on top of the write. Also I've discovered after
> much experimentation that the writes are not doing the job when it
> does not block up. Usually it blocks up after 3-4 write attempts. I
> expect I need to discover what is happening at the other end of the
> wire, but its my first experience of using a serial port for anything.
>
> I suspect there is an option I am not engaging in the setting up of
> the port. I am using the gpl version so I was thinking there could be
> a bug that is not in the gnat pro version, but I don't want to be a
> bad craftsman :) and gnat are usually pretty much on top of stuff like
> that from previous experience, but then again its a relatively new
> addition to the gnat compiler and no ones perfect. But.... its usually
> me.....

I suspect it's the speed setting.  Serial ports default to 9600 baud 
which is slow so you're filling the buffers up with the first few writes 
as they're unable to get the data out quick enough and then they start 
to block cos there's nowhere to put the data.

> Saying that though I am successfully reading from the port the
> incoming messages although they do appear in sections and I have to
> keep re reading the port to get the full message...

This is how serial interfaces usually work.  The lowest level read 
function returns the number of bytes actually read.