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POPython: What's the best way to send status bits and timestamps with PySerial
 

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  1. POPython: What's the best way to send status bits and timestamps with PySerial
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    <p>I have done a fair bit of searching and reading around but haven't found an exact clear answer. I am making python application which will communicate with another over the serial port. I have been using PySerial to accomplish this. The types of packets I want to send are status information and data readings. I am proposing to form of my packets as follows:</p> <pre><code>[ Start Byte ][ Length ][ Message ][ End Byte ][ Checksum ] </code></pre> <p>Although I don't think I need the end byte since have a length in there. Am I correct?</p> <p>I am thinking of shaping the 'Message' part of the packet for status info like so:</p> <pre><code>[ MsgTypeID ][ PacketID ][ Status Bits ][ Timestamp ] </code></pre> <p>The message ID here is just to differentiate that this is a status packet rather than a data packet. The status information itself is made up of 16 bits, representing the state of a number of subsystems in the sending application. For some of these subsystems, a single bit will provide enough info ('0' to say the subsystem is off/low/false, '1' for on/high/true). Others will require 2 or 3 bits (representing states and such). Prototyping the system up, I have been simply constructing a string concatenating the bits up to form a something like <code>'1001110101101100'</code> and sending this out the serial port, with the checksum being a modulo 256 of the status bits.</p> <p>I am pretty new to Python and serial communication but I know this is probably a waste of bandwidth. I know that PySerial has to send strings but representing each bit as a '0' or '1' like this is using a full string representation for each bit. I was wondering what is the best way to send these bits to reduce the bandwidth?</p> <p>For example, would I take each 8 bits, convert them to hex and send concatenated hex bytes, as in:</p> <pre><code>'10011101' + '01101100' </code></pre> <p>represented as</p> <pre><code>'\x9d' + '\x6c' </code></pre> <p>or should I send them as ASCII? I've also seen mentions of the Struct module. Should I be going down that route instead?</p> <p>The other thing I am wondering is how to represent the timestamp parts of the message.</p> <p>Any help, suggestions you can give me would be greatly appreciated.</p> <p>Thanks very much :) </p>
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