--- In digitalradio@yahoogroups.com, KV9U <[EMAIL PROTECTED]> wrote: > > Since I am not a programmer, other than taking some rudimentary courses, > reading some of Don Lancaster's books, and knowing that it is not > something I could ever do very well, something still doesn't seem right > to me when it comes to the claim that computers just can not meet the > timing requirements of ARQ digital modes. > > When I use the computer to key my ICOM 756 Pro 2 with Dave's DX Lab > Commander software in order to run other programs that interface with > Commander (such as Multipsk which is my main digital sound card > program), it does not seem to have much latency at all. And if one could > key relatively slow CW as is done with the software for the SDR1000, why > would that not be almost a magnitude faster than you would need for > adequate ARQ switching speed? > > How many ms do you need? > > Rick, KN6KB, the inventor of SCAMP, has said that the power in the > typical Windows OS computer we use is something like a magnitude less > than that available in the dedicated SCS modems and that is why they > perform so well compared to a computer (for the dedicated part). I > wonder where the dividing line will come so that computers will at least > match the SCS type units? > >
The problem is not that the PC's are not fast enough, it's that the timing of events is not predictable enough. In even the smallest microcontrollers, you can control the timing of events and processing down to a microsecond, if you so choose. For example, you can set the state of a pin, wait 8.76 milliseconds, change the state - and you KNOW that the state will be changed at that 8.76ms point, no if's, and's, or but's. In a typical PC OS, however, you lose that predictability. You can tell the OS, "I want to wait 8.76ms", so you can then go and change the state of the pin, but, in reality, you may not actually be able to do it for 8, 10, or 30ms later, because the OS is busy doing other things, in the meantime. Asking for an 8.76ms pause doesn't mean you'll GET an 8.76ms pause. I can't speak as to the accuracy of the posting that indicated that Windows has some facilities to accomodate real-time programming. If that's the case, I have to wonder why nobody has done it under Pactor I, at least, for Windows. Years ago, there were P-I *decoders* that worked under DOS. And now there's a P-I application for Linux called 'hfterm'. But, I've compared on-the-air performance between hfterm and my SCC PTC-II modem in P-I mode, and there's just no comparison - the SCS blows hfterm away. At least, so far. ;-) - Rich Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
