Re: [Boost-users] Asio problems with async_read

Subject: Re: [Boost-users] Asio problems with async_read
From: Alex Perry (Alex.Perry_at_[hidden])
Date: 2011-08-08 11:32:37

Allan Nielsen wrote on Mon, 8 Aug 2011 14:13:08 +0200
> Hi
> 
> I have a funciton where we I am using boost::asio to read from the
> serial port of my computer.
> 
> I have started out with an implementation which uses read, and I am
> now trying to convert it to async_read because I want a time out.
> 
> When I am trying to use the async_read version, I get timeouts after I
> have read one or two charterers, even though I know there are more
> charterers to be read on the wire.
> 
Not sure that this is much help since I've never really used boost.asio and reading further down the thread it may be a problem with how you are calling it. 

However having done a lot of serial comms in the past seeing a couple of characters only whilst more data is on the wire I'd guess that the timeout is as a result of the low level serial hardware interrupt. The UART is probably signalling that its internal FIFO buffer is full and you need to read this promptly - quite how that all pans out and what daemon / service has the responsibility of reading this these days I haven't got the faintest - I was writing TSR's when I knew the gory technical details of this so life was much simpler.

I'm actually impressed that you've found a computer that still has a serial port on it! Most seem to have gone over to the ubiquitous USB these days - though that may be the easiest solution - use USB and a usb/serial converter which would avoid having to rediscover the lost art of programming UART latch timings etc and give you a decent amount of low level buffering so you could ignore low level stuff and just read the data.

http://www.bb-europe.com/tech_articles/USB_converters.asp?gclid=CPvOgur5v6oCFRJc4QodMW7A5g or some such.

HTH 

Alex