VSS signal connected to TinyIOx or not?

http://jbperf.com/io_extender/index.html
http://jbperf.com/io_extender/tinyIOx.html for the TinyIOx
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jsiedlicki
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VSS signal connected to TinyIOx or not?

Post by jsiedlicki » Sat Nov 09, 2019 3:07 pm

I am looking to change my VSS input setup and have some questions about how different setups will impact the MS3 Pro performance i.e. mainloop times.

I am running an MS3 Pro and a TinyIOx for extra analog inputs currently. I am looking to add your Dual VR Conditioning board so I can input a signal from one of the front ABS VR sensor to be used for VSS.

To keep the MS3 mainloop times as low as possible, should I:

1. Connect the output of the VR conditioner to one of the timer 1 channels on the TinyIOx and setup TunerStudio to poll the PWM inputs and select "Use CAN PWMin" for the Speed and Gear Sensor system input?

Or

2. Connect the output of the VR conditioner into one of the spare digital switched inputs of the MS3 Pro and use that for the Speed and Gear Sensor system input?

Is there any performance gain by having the conditioned signal go into the TinyIOx and then picked up by the MS3 Pro via CAN compared to connecting the conditioned signal directly to the MS3 Pro ecu?

John

jbelanger
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Re: VSS signal connected to TinyIOx or not?

Post by jbelanger » Sat Nov 09, 2019 6:33 pm

The first thing is to establish which function(s) you want the VSS to be used for. Is it only for logging vehicle speed or do you also want to use the speed for other things such as traction control? That's more important than whether or not the mainloop time is increased. And, by the way, I won't be able to tell you if there is a significant impact on that because I don't have an intimate knowledge of the MS3 code nor do I have access to the latest code.

Second, there will always be some latency when using CAN data and this latency will have some variabilty. So if you need to react as quickly and consistently to the speed such as when using traction control, using a direct MS3 input will be better. On the other hand, the TIOx has much more flexibility in the timer settings so that in theory it should allow a more precise speed data. That also depends on the frequency of your VSS signal (related to the number of teeth).

So start with those and we can go on from there.

Jean
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jsiedlicki
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Re: VSS signal connected to TinyIOx or not?

Post by jsiedlicki » Sat Nov 09, 2019 7:47 pm

I am not using traction control, I am interested in logging only. The ABS wheel has 44 teeth but I was considering reducing that to 11 as I do not think I need that high a resolution. My assumption is that it would reduce the processing load on either the MS3 Pro or the TIOx, depending on how its hooked up.

My thought is that since my MS is already polling for the ADC data, adding polling for the PWM in from the TIOx shouldn't add any significant overhead to the MS? Where as if I connect the signal directly to the MS, the ecu will have to poll for the input on the digital switched in port as its not interrupt driven.

Am I thinking this through correctly?

jbelanger
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Re: VSS signal connected to TinyIOx or not?

Post by jbelanger » Sat Nov 09, 2019 8:12 pm

You're correct that reducing the number of teeth will lower the amount of processing on either the TIOx or the MS3 when the input is directly connected to it.

However, it is not correct that having polling already for the ADC means that polling for the PWM input will not add significant overhead. There is practically no overlap between the 2 functions so you will have more CAN traffic and more processing when you add more polling. The only time this would be correct is if you were going from using less than 4 ADC channels in one ADC group to all 4 channels in the same group.

But I could not tell you if CAN polling for PWM inputs is more or less processor intensive than adding a digital input.

I think you might be overthinking this. You should probably use the input that is easier for you to do. And if you do not want to change the number of teeth, you should probably go with the TIOx input because that will allow you much more resolution for a higher frequency signal. It will increase processing on the TIOx but unless you're already using many features, that should not be an issue.

Jean
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jsiedlicki
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Re: VSS signal connected to TinyIOx or not?

Post by jsiedlicki » Sat Nov 09, 2019 8:29 pm

jbelanger wrote:
Sat Nov 09, 2019 8:12 pm
I think you might be overthinking this. You should probably use the input that is easier for you to do.
I think your right :lol: I think I'll go for the setup that is the simplest to wire up.

Thank you for the background information.

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