Innovate Motorsports OT-2 SDK - Manual (Page 32)

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Understanding OT-1b/2 Device Configuration
To fully understand the Device Configuration (which can be obtained with the ‘c’
command, and set with the ‘C’ and ‘M’ commands documented in the previous section),
we need to take a step back and look at some MTS/OBD-II conflicts.
To start with, different OBD-II PIDs return different size values, often with huge ranges.
But, unless you jumped over the long and tedious first sections, you know that MTS Aux
Channels are limited to 10 bits (0-1023) for full range.
A second problem is that ECU response times vary wildly, but the MTS ‘timeline’ keeps
ticking at 81.92 milliseconds. We concluded that it was too much to expect the user to
directly deal with both these problems, so we addressed the first one by creating a layer
of abstraction between the user and actual ECU PIDs. We call these ‘virtual’ PIDs,
‘normalized’ PIDs, because they have been scaled to fit into our 10 bit samples and
typical scales for certain values. A table of these ‘Normalized PIDs’, along with their
ranges and associated ECU mode 1 PID can be found in Appendix A.
The problem of ECU performance we partially address by giving the user some tools. For
example, the Vehicle led blinks at the same scale that we use for the MTS light, so users
can get a visual indication on how the polling speed of their selected normalized PIDs
compares to the fixed MTS sample rate. Software can make a similar comparison using
the ‘l’ (Get Last OBD-II loop time) command. We also use the PID mask returned from
the connection status command (‘j’) to determine which normalized PIDs to present to
the user.
Last, we give the user a simple priority mechanism. Individual channels can be normal
priority – polled once each loop, or low priority. Only one low priority channel is polled
each time through the loop. So, if the ECU supports 4 channels at acceptable rate, 3 can
be used for critical values, and the 4
th shared for multiple low rate channels, like various
temperature readings.
Some simple diagrams of this scheme can be found in the OT-x
manuals. Normal priority channels are read one after another in a
loop.
The more channels you add, the slower the loop.