On Thu, Jan 20, 2011 at 08:42:58AM -0500, James Y Knight wrote:
I don't think you'll ever be able to do this reliably in Python. At 9600 baud, 3.5 characters is just about 275hz (9600/10/3.5). Linux schedules process at around 500hz.
Well, that's bad news - I'll have to communicate with the SPS at 38400 baud :-(...
On the other hand, are you sure you need this? http://www.libmodbus.org/ seems to have code which figures out what length packets should be, and no code to detect a 3.5char delay between packets. That seems much more reliable.
Thanks for the hint - I'll have a look. The code seems quite readable, although I don't exactly _love_ reading C sources. But the idea that one might still find out where a modbus message ends is intriguing - I don't yet see how this might work.
It also doesn't seem to have any code to ensure a 3.5char between sent packets
Not sure about this - there is a structure called ctx which has a timeout_begin->tv_sec and timeout_begin->tv_usec (and a similar thing for timeout_end). On the first glance, this looks like variables for handling the boundary. But I might be wrong. Thanks & best regards, Albert -- Albert Brandl Weiermayer Solutions GmbH | Abteistraße 12, A-4813 Altmünster phone: +43 (0) 720 70 30 14 | fax: +43 (0) 7612 20 3 56 web: http://www.weiermayer.com