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Originally Posted by MasterMentor
On the contrary, I think I figured it out directly from the FMS Whitepaper.
From the FAQ, "Does the FMS Control the Robot", FMS sends the commands to the DS, which then forwards the command to your robot to start.
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Does the command get sent to all 6 DS laptops at the same time? The server in the scorpian case has one ethernet port for all red and one ethernet port for all blue robots. Does the software send red and blue simultaneously, or is there a single network adapter + a switch for both red and blue, meaning one must be sent before another. How much time is between these two commands? Within the separate red/blue disable commands the 1, 2, and 3 station enable commands must happen serially. Are they sent immediately after each other, and if not, what is the delay.
It might seem a silly question to ask if there is a significant delay between sending red and blue side commands, but hey, that's exactly what happened last year with the hot goal lights, which were +/- 4 seconds in terms of accuracy at times.
These ethernet cables run to control cases (SCC's) under the DS shelf, where they plug into an ethernet switch. This ethernet switch is connected to an Allen Bradley Stratix 8000, which has three other ethernet ports that are dedicated to 1, 2, and 3 driver stations. What goes on here is unknown, but it's not unreasonable to expect that there could be delays here. The Allen Bradley box is doing something other than being a switch because it won't work if you plug the wrong team into the wrong ethernet cable.
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While it's not explicitly stated, most command systems have a processing loop that will "process" incoming commands at a known rate (timed so you don't chew up your CPU). Now, even if we knew the loop rate we don't know where in the loop the command will come in; will the command arrive immediately at the beginning of that loop, in the middle, or at the end?
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It depends on how the polling is set up. If they check for 'FMS says enable' every time they send the command (20 ms), then timing can't be accurate to more than 20 ms, as you pointed out.
The FMS software and DS are written in C# (or c++, I forget), and LabVIEW, both of which easily support event driven behavior, meaning the driver station may respond to an FMS command as soon as the network buffer reads in the message.
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That's probably the difference - I'd bet the difference in time it takes FMS to issue the command across all the VLANs to the DS's would be in the nanosecond (microsecond for sure) range.
-MM
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You'd think, but the difference in time it took the FMS to send commands to the phillips lighting controller last year was sometimes greater than 2 or 3 seconds. FMS timing seems to be properly understood by nobody.