Automon Kernel Considerations

Automon Architecture

Automon Architecture

The Automon kernel will be responsible for all the lower level ELM327 serial communication. It will provide a easy to use interface to communicate with any ECU encapsulating all ELM327 commands.

One of the design issues problems I am encountering is that not all responses from the ELM327 are “simple”.  Most sensor commands result in a few bytes represented in hexadecimal and you apply a formula to get the actual human result in volts, rpm, degrees etc. Some results however are bit encoded. For example a request to Mode 3 of “03″ without a Pid results in a stream of bytes, with the first byte meaning how many DTCs are present and the remaining types of DTCs, where each is encoded to a special type, P, U, B codes etc and which are pending or not is also encoded into the bytes. I wanted to create a generic PID base class but the complications is causing problems. I want to allow the user to provide proprietary codes as well. To do this I would read the codes from a file but how do I specify the formula and the logic in the formula if it exists? – For example, some formula’s have, If Byte B == 0xFF (all 1s), then it means this, other wise take byte A and do something else. One solution would be to using scripting. QT provides a useful scripting engine in the QScript module. I might look into this and get a better understanding of it.
Alternatively, if I want to make my system less flexible, I could create a Sensor class and derieve each sensor over writing a “convert formula” method so each class of sensor has its own defined formula.
Since the data structure holding these is so vague and none standard across all sensors, I thought XML would be a great way of representing this data for parsing later.

Today I managed to convert my GUI prototype app into one that can handle a QList<Sensor> of sensors. I also implemented a way of how frequent sensors get updated. For example, RPM,MPH are the main ones that change down in milliseconds but something like coolant temperature would only need to be checked maybe every few sensor cycles. A sensor cycle is where my serial comm thread iterates through a list of sensors. Every time it comes to a sensor, it evaluates if it time to check that sensor, otherwise skip to next. This makes adding sensors quite handy. I also created signals in my sensors, so once their value changes, they automatically emit a signal with the new value. This is very useful since I can connect sensors to GUI slots very simply. Here is an example:

sensor = new AGenericSensor();
sensor->setEnglishMeaning(“Engine Revolutions per minute”);

sensor2 = new AGenericSensor();sensor2->setEnglishMeaning(“Engine Coolant Temperature”);


connect(sensor, SIGNAL(changeOccured(QString)), this, SLOT(updateLCDText(QString)));
connect(sensor2, SIGNAL(changeOccured(QString)), this, SLOT(updateLCDText(QString)));

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