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138 | -- Fixed length message services using the Stream Framing Protocol.
-- Must be instantiated for each message size.
-- Copyright (C)2021, Philip Munts, President, Munts AM Corp.
--
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are met:
--
-- * Redistributions of source code must retain the above copyright notice,
-- this list of conditions and the following disclaimer.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-- POSSIBILITY OF SUCH DAMAGE.
WITH Stream_Framing_Protocol;
PACKAGE BODY Messaging.Fixed.Ada_Streams IS
PACKAGE SFP IS NEW Stream_Framing_Protocol(MessageSize);
DLE : CONSTANT Messaging.Byte := 16#10#;
STX : CONSTANT Messaging.Byte := 16#02#;
ETX : CONSTANT Messaging.Byte := 16#03#;
-- Constructor
FUNCTION Create
(stream : NOT NULL Ada.Streams.Stream_IO.Stream_Access;
trimzeros : Boolean := True) RETURN Messenger IS
BEGIN
RETURN NEW MessengerSubclass'(stream, trimzeros);
END Create;
-- Send a message
PROCEDURE Send(Self : MessengerSubclass; msg : Message) IS
msglen : Natural;
frame : SFP.FrameBuffer;
framelen : SFP.FrameSize;
BEGIN
msglen := msg'Length;
-- Optimize bandwidth by not sending trailing zeros. For short
-- messages, this will greatly reduce channel bandwidth
IF Self.trim THEN
WHILE (msglen > 0) AND (msg(msglen - 1) = 0) LOOP
msglen := msglen - 1;
END LOOP;
END IF;
-- Encode the frame
SFP.Encode(msg, msglen, frame, framelen);
-- Send the frame
Messaging.Buffer'Write(Self.stream, frame(1 .. framelen));
END Send;
-- Receive a message
PROCEDURE Receive(Self : MessengerSubclass; msg : OUT Message) IS
b : Messaging.Byte;
DLE_count : Natural := 0;
frame : SFP.FrameBuffer;
framelen : Natural := 0;
payload : SFP.PayloadBuffer;
payloadlen : SFP.PayloadSize;
BEGIN
LOOP
Messaging.Byte'Read(Self.stream, b);
CASE framelen IS
WHEN 0 =>
IF b = DLE THEN
frame(1) := DLE;
framelen := 1;
DLE_Count := 1;
ELSE
framelen := 0;
DLE_Count := 0;
END IF;
WHEN 1 =>
IF b = STX THEN
frame(2) := STX;
framelen := 2;
ELSE
framelen := 0;
DLE_Count := 0;
END IF;
WHEN OTHERS =>
IF b = DLE THEN
DLE_Count := DLE_Count + 1;
END IF;
frame(framelen+1) := b;
framelen := framelen + 1;
END CASE;
-- Check for complete frame
EXIT WHEN framelen >= 6 AND THEN (DLE_count MOD 2 = 0 AND
frame(1) = DLE AND
frame(2) = STX AND
frame(framelen-1) = DLE AND
frame(framelen) = ETX);
-- Check for buffer overflow
IF framelen = SFP.FrameSize'Last THEN
framelen := 0;
DLE_Count := 0;
END IF;
END LOOP;
SFP.Decode(frame, framelen, payload, payloadlen);
msg := payload;
END Receive;
END Messaging.Fixed.Ada_Streams;
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