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The approach to datalogging taken by DSMLink is very different from other dataloggers on the market. Typically, a datalogger will get its data one piece at a time by asking the ECU for something, recording it, then asking for something else. This is relatively wasteful in that a two-way conversation has to take place for every little piece of data being captured. This also introduces some amount of value creep in that each value is being recorded at a slightly different time relative to the other values. DSMLink, however, captures data in "frames". A frame of data is a collection of values bundled together. DSMLink takes a snapshot of all the values it's going to capture at the same instant inside the ECU, then streams that data block to the laptop. This makes calculations outside the ECU about as accurate as they can be. DSMLink also records the time, inside the ECU, of each snapshot, accurate almost to the microsecond (0.000001 seconds). This also helps ensure that the values being calculated by the laptop are as accurate as they can be. DSMLink eliminates the need for two-way conversation by defining a "streaming mode". When the user wants to start capturing data, the laptop requests that the ECU go into "streaming mode", sending data to the laptop non-stop. When the user wants to stop capturing data, the laptop requests that the ECU stop sending data. This streaming approach helps to squeeze every last bit of throughput from the serial connection, ensuring data capture rates are as fast as they can be. In order for this streaming, frame-based mode to work, the ECU and laptop must both know exactly what's being captured before the stream starts. The ECU keeps two tables of values for this purpose. The first is a hard-coded table of values that are always included in the data stream. The second is a variable list that's defined by the user to augment the first. The laptop reads these tables before starting the stream operation so that it knows exactly what the ECU will be sending. The dialog below is used to define this set of parameters.
See the DSMLink User's Guide for more information about the stream data dialog box and how to display values. You'll also find a complete list of the displayable values along with a brief description of each in the user's guide. |
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