4 ms·

As I see it there are two properties of a networked system this can possibly enhance: (1) predictability, and (2) a reduction in overall latency. On the former

As I see it there are two properties of a networked system this can possibly enhance: (1) predictability, and (2) a reduction in overall latency. On the former it is only a small part of any goal or guarantee of total predictability. On the latter we should note that it is of significantly decreasing importance as bandwidth increases, which Ethernet enhances greatly, particularly on low node systems with relatively low bandwidth requirements, which covers most industrial deployments. Therefore it's sort of a 'meh' feature outside of specific requirements.

monocasa 7y ago
Which is why you see it heavily used in distributed real time systems where those guarantees are valuable, even at the expense of raw throughout.
- rurban 7y ago
  And that why you see more and more Gigabit Ethernet replacing stone-aged protocols such CAN, Profibus or Firewire, because a simple Ethernet Chip is dead cheap, >100x faster and comes with a modern memory-mapped driver, the others not. It makes hard real time latency and throughput much easier. With CAN you cannot get very far, and the typical CAN multiplexing tricks get dirty very soon.
  - monocasa 7y ago
    You can get CAN to go pretty far. And real time latency is not "dead simple". A low priority message will always lose out to a higher priority message on CAN. With ethernet a low priority task can flood the bus if the circumstances are right. Also, which MCUs come with gigabit ethernet?
    - rurban 7y ago
      Formula 1 only so far, but the idea was to get beefier ones sooner or later.
      - monocasa 7y ago
        I'm sorry, I don't quite follow. Can you reiterate?
        rurban 7y ago
        Q was which MCU's come with Gigabit Ethernet. I answered the Formula 1 MCU's (Motor Control Unit). Maybe the official one from Illmore already (I think), and some of the internal ones used for testing (which I worked with). The NASA Space Shuttle also had several dSpace controllers on board (RTLinux with special IO drivers) and I guess modern rockets and planes also will switch to Ethernet also. It's 1MHz vs 1GHz. It makes a difference when you can afford a fast CPU, i.e. high speed controller and you don't want to wait for CAN messages coming in every 1000 cycles.

monocasa 7y ago

Which is why you see it heavily used in distributed real time systems where those guarantees are valuable, even at the expense of raw throughout.

rurban 7y ago
And that why you see more and more Gigabit Ethernet replacing stone-aged protocols such CAN, Profibus or Firewire, because a simple Ethernet Chip is dead cheap, >100x faster and comes with a modern memory-mapped driver, the others not. It makes hard real time latency and throughput much easier. With CAN you cannot get very far, and the typical CAN multiplexing tricks get dirty very soon.
- monocasa 7y ago
  You can get CAN to go pretty far. And real time latency is not "dead simple". A low priority message will always lose out to a higher priority message on CAN. With ethernet a low priority task can flood the bus if the circumstances are right. Also, which MCUs come with gigabit ethernet?
  - rurban 7y ago
    Formula 1 only so far, but the idea was to get beefier ones sooner or later.
    - monocasa 7y ago
      I'm sorry, I don't quite follow. Can you reiterate?
      - rurban 7y ago
        Q was which MCU's come with Gigabit Ethernet. I answered the Formula 1 MCU's (Motor Control Unit). Maybe the official one from Illmore already (I think), and some of the internal ones used for testing (which I worked with). The NASA Space Shuttle also had several dSpace controllers on board (RTLinux with special IO drivers) and I guess modern rockets and planes also will switch to Ethernet also. It's 1MHz vs 1GHz. It makes a difference when you can afford a fast CPU, i.e. high speed controller and you don't want to wait for CAN messages coming in every 1000 cycles.