Re: GNAT.Serial_Communications

[tonyg <tonythegair@gmail.com>]

On Apr 14, 6:52 pm, Chris Moore <zmo...@ntlworld.com> wrote:
> 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.

I found the problem. Its very embarassing and completely my own fault!
Basically I did not have the write access to the usb port! I am using
ubuntu for this. Just to let those who are interested know.