> From jsoi@gis.joensuu.fi  Wed Sep 14 23:32:31 1994
> 
> Hi !
> 
> The problem with linux and v.digit is set_key.c-file. With linux you should use
> some bsd-stuff. Furthermore you have to add -lbsd when linkng v.digit
> 
> There is still something wrong with linux and digitizing boards:
> It works once (if it works at all) with same post configuration.
> (/dev/ttyS0 etc.). If you try to use it another time the programs stops.
> 
> I donno if it is v.digit or linux which causes this problem.
> 
> Here is the set_key.c-file I got from Andy Burnett
> 
> (I posted this to D. Gerdes also)
> 
> Hope this helps you !

Thanks for the code.  As for digitizers working with PC boxes, 
I believe it all comes down to the serial board.  When I did the port
to Microport the standard serial cards would lose information in 
a multitasking environment.  I don't know that the software is any better
today.  The problem is that cheap serial cards buffer at most I believe
16 bytes of data.  If the OS doesn't give time to servicing incoming
serial data before the buffer fills up, the data will be lost.  Once you
start dropping characters from a digitizer, the software more than
likely is going to be out to lunch.  We never wrote it to try to recover
from major comunication failures.

The solution that I chose was to by a third party 'intelligent' serial
card.  These typically have their own cpu and buffers, and come with
kernel drivers a specific OS.  The one we used was from Digiboard.
This worked very well.

If you dont want to go that way (or can't if they don't support Linux),
getting a 16550 UART which has at least a small buffer, and setting your
baud rate very slow, like 300 baud.  I don't know off hand how well the 
current digitizer interface works if it drops an occasional character.



-- 
  David Gerdes
  US Army Construction Engineering Research Lab
  Spatial Analysis & Systems Team
  dpgerdes@zorro.cecer.army.mil

   
     Currently at:
      
      USDA Soil Conservation Service/TISD
      2625 Redwing Rd, Suite 110
      Ft. Collins CO  80526-2878
      (303) 282-2917


