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<title>Serial-line communication in TinyOS-1.1</title>
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<font face="tahoma,arial,helvetica"><b><big><big>Serial-line communication in TinyOS-1.1</big></big></b>
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Last updated 03 Sep 2003
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<td width="100%"><b><font face="arial,helvetica">Description</font></b></td>
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<p><i>Protocol:</i></p>
<p>The protocol used by TinyOS-1.1 is loosely based on the PPP in HDLC-like
framing described in RFC-1662. It uses the same framing and escape
sequences and a 16-bit CRC. The protocol always assumes
Address-and-Control field compression. The implementation understands the
Protocol IDs in Table 1. All other protocols are rejected.</p>
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<td width="25%" align="center"><b>Id</b></td>
<td width="11%" align="center"><b>Value</b></td>
<td width="64%" align="center"><b>Description</b></td>
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<td width="25%"><tt>PROTO_ACK</tt></td>
<td width="11%">64 (0x40)</td>
<td width="64%">An acknowledgement packet. Typically sent by the TinyOS
device back to the host backend. The packet consists of a one byte
payload which is the token of the corresponding packet being acknowledged.</td>
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<td width="25%"><tt>PROTO_PACKET_ACK</tt></td>
<td width="11%">65 (0x41)</td>
<td width="64%">A data packet that expects a subsequent ACK packet.
The first byte of the payload contains the token that must be returned in
the ACK.</td>
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<td width="25%"><tt>PROTO_PACKET_NOACK</tt></td>
<td width="11%">66 (0x42)</td>
<td width="64%">A data packet that does not require a subsequent ACK packet.</td>
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<td width="25%"><tt>PROTO_UNKNOWN</tt></td>
<td width="11%">255 (0xFF)</td>
<td width="64%">A packet sent by a receiver when it receives a packet of an
unknown/unsupported protocol</td>
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<p align="center"><b>Table 1: Known framer protocol types.</b></p>
<p><i>Components:</i></p>
<p>The following components implement the framing protocol on the TinyOS device:</p>
<blockquote>
<p><b><tt>FramerM</tt>:</b> The TinyOS module that provides the core framing protocol. It
provides the <tt>BareSendMsg</tt>, <tt>ReceiveMsg</tt> and <tt>TokenReceiveMsg</tt> interfaces. The
<tt>TokenReceiveMsg</tt> interface is used when handling packets that require
acknowledgements. The interface extends the <tt>ReceiveMsg</tt> interface by
including a field for the token on the receiver and a new command,
<tt>ReflectToken()</tt>, that triggers the ACK process. The use of acknowledgements
is intended as a simple flow control scheme to prevent exceeding buffering
capacities on a TinyOS device.</p>
<p><tt><b>FramerAckM:</tt></b> A generic module that implements ACK processing for inbound
packets. It is intended to be used in lieu of applications that
specifically handle ACKs. </p>
<p><b><tt>UARTFramedPacket:</tt></b> A configuration component that incorporates both <tt>FramerM</tt>
and <tt>FramerAckM</tt>. It exports the same interface as <tt>UARTNoCRCPacket</tt> and can
be used interchangeably with that component. The default UART communication
provider for <tt>GenericComm</tt> in TinyOS-1.1 is <tt>UARTFramedPacket</tt>.</p>
</blockquote>
<p><i>Applications:</i></p>
<p>The following applications are provided for simple interfacing to a TinyOS
network:</p>
<blockquote>
<p><b><tt>TOSBase (apps/TOSBase)</tt></b>: An application that acts as a simple bridge between
the serial and wireless channel. It is similar to the older <tt>GenericBase</tt>, but
incorporates <tt>FramerM</tt>. TOSBase does not use <tt>FramerAckM</tt>, but implements
it's own ACK handling. Specifically, TOSBase will only ACK a packet
received from the serial channel once it has been transmitted over the radio.
TOSBase will only bridge those packets whose group id matches the value of the <tt>TOS_AM_GROUP</tt>
value compiled into the application.</p>
<p><b><tt>TransparentBase (apps/TransparentBase)</tt></b>: A bridge identical to <tt>TOSBase</tt>,
except that it does not filter packets based on group id.</p>
<p><b><tt>GenericBase (apps/GenericBase)</tt></b>: The legacy bridging application that does
not provide for framing or flow control. </p>
</blockquote>
<p><i>Host Tools:</i></p>
<p>There are a variety of java-based tools that can be used to simplify serial
communication using the new protocol. They include classes and a simple
application, <tt>SerialForwarder</tt>. A key point with these tools is that they
understand how to communicate with multiple types of <i>packet sources</i>.
These include directly attached serial links, network links and simulated links
using either the framed or legacy protocols. See the <a href="#Usage">Usage</a>
section for more information on the specific types of packet sources.</p>
<blockquote>
<p><b><tt>net.tinyos.packet.PacketSource</tt></b> (Interface): This class provides a series of
standards methods to communicate with a TinyOS node on a per-packet basis. It provides the basic semantics of open, close, readPacket and writePacket.
Refer to <tt>tools/java/net/tinyos/packet/PacketSource.java</tt> for more information.</p>
<p><b><tt>net.tinyos.packet.PhoenixSource</tt></b> (Class): This class provides some
additional functionality above the standard PacketSource. PhoenixSource
spawns a thread that will initiate an upcall whenever a new packet arrives
from a serial channel. In the case of network based links, it will
attempt to reconnect to the channel if connectivity is lost. Refer to
toos/java/net/tinyos/packet/PhoenixSource.java for more information.</p>
<p><b><tt>net.tinyos.sf.SerialForwarder</tt></b> (Application): The SerialForwarder acts as a
relay point between any packet source and network packet source. It's
intended use is to provide TCP/IP connectivity to a locally connected TinyOS
device. The <tt>SerialForwarder</tt> provides the capability of multiplexing
multiple network connections into a single connection. That is, multiple
remote applications can connect to a TinyOS node via the <tt>SerialForwarder</tt> (no
deterministic serialization is provided, however).</p>
</blockquote>
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