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From: tilmanglotzner@my-deja.com
Subject: how to access a (serial) device (linux)
Date: 2000/01/27
Message-ID: <86op66$lu9$1@nnrp1.deja.com>#1/1
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Date: 2000-01-27T00:00:00+00:00
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Hello,

I wrote a program to access serial port via the device file. One
task reads on the port, another task writes to the port. The
tasks somehow seem to block each other, and an antenna controller
connected to the serial port does not receive anything.

1) Is accessing the serial port via a device file the wrong approach ?
Is it better to do this by an interrupt service routine ? A sample
which I could reuse would be very, very helpful here :-)

2) Maybe the processes are in a dead lock because 2 processes try to
access the same file. Is it feasible to access a device file from 2
task  ?

3) Maybe it is better to access the device file from only 1 task.
I would need to open the file as read/write. Text_io seems not be
capable of this.Are there other packages which allow opening
(device) file as read/write ?

Thanks,

Tilman

=== Here the code ============================
with Text_IO;use Text_IO;
with System; use System;

package body Ser_read is
   package Int_Io is new Integer_IO (Integer); use Int_Io;


   task body Read is
      ReadPtr  : File_Type;

      Str      : String(1..100);
      Az       : String(1..20);
      El       : String(1..20);

      DeviceB  : String := "/dev/ttyS0";
      End_Flag : Boolean := False;
      I        : Integer;
      LineCount: Integer := 0;
      Wait     : Duration := 1.0;

   begin
      Put_Line ("[Read] : Started");
      while (End_Flag = False) loop
         select
            accept Init do
               Put_Line ("[Read] : Open " & DeviceB & " for read ...");
               Open (ReadPtr,In_File,DeviceB,"SHARED=NO");
               Put_Line ("[Read] : Opened for Read " & DeviceB);
            end Init;
         or
            accept Read_Orientation do
               Put_Line ("[Read] : Read_Orientation Signal received");
               Write.Send_Command("C2");
               Put_Line ("[Read] : Reading from " & DeviceB & ";");
               Get_Line(ReadPtr,Az,I);
               -- Get_Line(ReadPtr,El,I);
               Put_Line("Azimuth  : " & Az & ";");
               Put_Line("Elivation: " & El & ";");
            end Read_Orientation;
         or
            accept Stop do
               Put_Line ("[Read] : Stop Signal received");
               End_Flag := True;
            end Stop;
         end select;
      end loop;
      Put_Line ("[Read] : Close "  & DeviceB);
      Close (ReadPtr);
      Put_Line ("[Read] : Closed "  & DeviceB);
      Put_Line ("[Read] : Terminating task ...");
   End Read;

   task body Write is
      WritePtr : File_Type;
      DeviceA  : String  := "/dev/ttyS0";
      End_Flag : Boolean := False;


   begin
      Put_Line ("[Write] : Started;");
      while (End_Flag = False) loop
         select
            accept Init do
                     Put_Line ("[Write] : Open " & DeviceA & " for
write ...");
                     Open (WritePtr,Out_File,DeviceA,"SHARE=NO");
                     Put_Line ("[Write] : Opened for Write " & DeviceA);
            end Init;
         or
            accept Send_Command(Comm: in String) do
               Put_Line ("[Write] : Command Signal received: " & Comm &
";");
               Put_Line (WritePtr,Comm);
               Put_Line ("[Write] : Command sent: " & Comm & ";");
            end Send_Command;
         or
            accept Stop do
               Put_Line ("[Write] : Stop Signal received");
               End_Flag := True;
            end Stop;
         end select;
      end loop;

      Put_Line ("[Write] : Close " & DeviceA & " ...");
      Close (WritePtr);
      Put_Line ("[Write] : Closes " & DeviceA );
      Put_Line ("[Write] : Terminating task ...");
   end Write;
end  Ser_read;

=========== and the code of the main program
With Text_IO; use Text_IO;
with Ser_read;

procedure SerialOpen is
   FilePtr  : Text_IO.File_Type;
   CStr     : String (1..8);
   I        : Integer;
   C        : Character;


begin
   Put_Line ("[Main]: Start");
--   Ser_Read.Read.Init;
   Ser_Read.Write.Init;


   CStr := "W020 015";
   Put_Line ("[Main]: Initiate rotor command: " & CStr(1..CStr'Last));
   Ser_Read.Write.Send_Command(CStr);


   Put_Line ("[Main]: Press <CR>");
   Get (C);
   Put_Line ("[Main]: Initiate rotor command: C2");

 --  CStr := "C2";

   Ser_Read.Read.Read_Orientation;

   Put_Line ("[Main]: Press <CR>");
   Get (C);

   CStr := "W000 000";
   Put_Line ("[Main]: initiate rotor command: " & CStr(1..CStr'Last));
   Ser_Read.Write.Send_Command(CStr);

   Put_Line ("[Main]: Initate termination of Read task.. " );
   Ser_Read.Read.Stop;
   Put_Line ("[Main]: Initate termination of Write task.. " );
   Ser_Read.Write.Stop;
end;



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