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Flexray to Optical fiber communication

Hello All,

Currently, We are developing a product based up on TMS570 Microcontroller for safety critical application.

We want to convert the Flexray communication to Optical Fiber single mode communication for longer distance

What are the necessary things to take care during my hardware design?

Kindly give your valuable feedback.

Thank you.

Regards,

S.Saravanakumar

  • Hey Saravanakumar,

    I apologize for the delay, your messaged failed to get assigned to someone it would look like and now I've stumbled across it. Can you give me the MCU model of the TMS570 that you are using? Are you planning on using the 2 or 4 wire variant of Flexray?

    If you use the two wire variant then it will be pretty straightforward to do and can go in depth once you provide the specifications I seek. Four wire will be more complicated but we can certainly look to see if I can find a solution!

    Best Regards,
    Nick
  • In reply to Nicholas Mariani9:

    Hey Nicholas,

    Thank you for taking considering the below clarification.

    We are using TMS570LS1227 Microcontroller for our application.

    We want to send the data either from flexray 2 wire or 4 wire, to optical fiber communication in Single mode. At least to drive minimum 10 Km - 20 Km distance via optical fiber.

    We are looking for the feasible solution either with flexray 2 wire or 4 wire

    Thank you.

    Regards,

    S.Saravanakumar

  • In reply to Saravanakumar S93:

    Hey Saravanakumar,

    Haha, what are you building a doomsday machine control system?! In all seriousness though, I’m very curious what application would need to use Flexray at 10Mbps across 10 or 20Km; if you can’t say due to IP reasons don’t worry about it, just intriguing is all. Anyway, I have split this post up into three to avoid the brick wall of text effect.

    My first question pertains to the application, before going any further I just wanted to check that this method of communication will beat out any other wireless or hardware signal. There are a lot of options these days for carrying that bandwidth. Gigabit Ethernet for example is clocked in at 100x speed boost for you signal. It may not have the rock solid packet dropping record that Flexray does but it’s in the high 90s for successful packet transmission. Installing 20km of single mode fiber is essentially like laying the start of a network backbone fiber. It will be incredibly costly if burying the line and incredibly costly if just 20km of line in some over air or snaking through building walls.

    If you’re sure you’d like to proceed down this route, what level of customization are you looking to use. Essentially, would you like to use consumer off the shelve products (COTS) or are you wanting to make your own optical systems for this down to the laser drivers for this project of yours? Do you want to be able to carry other information besides just Flexray? Seems non-optimal to use 20km of high end single mode fiber to carry 10Mbps max throughput, perhaps there is a need to carry an Ethernet signal and we can do some multiplexing for you or something? You can ignore most of this; I just want you to get the most out of such an awesome cable line. Anyway, with all of that out of the way onto the real info for you!

    In the information below I will give you an upper level view of what you need to do to get this system setup. I’m going to make two assumptions, the first being that you want to use COTS hardware. If you do want to design your own hardware for it let me know and I can help you out with that too! The second assumption that I’m making is that this specific run will be point–to–point and not a multi-drop connection (for this cable run). If this is not true let me know and we can try to adjust for that.
  • In reply to Saravanakumar S93:

    Two-Wire Transmission:

    Luckily, doing a fiber transmission for a two-wire Flexray setup shouldn’t be terribly difficult. I am going to recommend that you use COTS 1000BASE-EX Ethernet hardware. Everything on the market should be built and guaranteed to work at this IEEE spec and meets your distance requirements. This spec can run to ~40Km over single mode fiber using the 1310nm wavelength as the carrier.

    The key to understanding optical communications is that the crux of the problem is taking interfaces with many wires and data channels down to one channel for all of them. Traditionally this is down using serializers and deserializers (SERDES) to shift all of this data into one transmission path. This Transmission path is comprised of a Tx and Rx pair. In practice a challenging task because compressing data lines together and maintaining the transfer speeds of the protocol requires a SERDES signal that can switch at a speed equaling the sum of all the aggregated data rates. For example, gigabit Ethernet runs at a 125MHz over four channels, which is actually125Mbaud and each symbol transmitted contains two data bits of data but this is a topic for another day, resulting in a total of 250Mbps over four differential pairs. Anyway, the switching frequency of this system can be relatively slow at the 125MHz rate but if we want to reduce it to one Tx/Rx pair then we need to boost our switching speed to 1.25GHz, a ten fold increase in speed.

    Fortunately, the SERDES conversion doesn’t need to be done since the two-wire configuration is of Flexray is already a high speed differential serial link! You will need to break up the signal however into one Tx channel and one Rx channel since you can’t have bidirectional transmission on an optical fiber. This can be done with an analog DPDT switch that goes to the Tx channel when transmitting and switches to the Rx channel when receiving. The rest will be taken care of by the SFP modules form the Ethernet standards, which should provide you the power needed to traverse the 10 to 20km run.
  • In reply to Saravanakumar S93:

    Four-Wire Transmission:

    I originally thought that the four-wire version of Flexray was just more signal content. Now, it seems from what little online information I’ve found online that the four wire version is just one differential pair for transmission and a second for receiving. Can you verify this for me, I can’t seem to find any non-two-wire info on the web. If this is accurate then I would recommend going with the four wire variant since it will be easier than the two. You should be able to make a board that routes into an SFP module and don’t even need to bother with switching.

    If this answered your question please verify each of the solutions by hitting the green verify button at the bottom of each post! If you have more questions, please feel free to send them along and I will try to answer them or clarify information presented.

    Best Regards,
    Nick
  • In reply to Nicholas Mariani9:

    Hey Nicholas,
    Thank you very much for the detailed feedback and split up options.
    Your proposal given different feasible options.
    Please find the communication architecture of our product.This is based up on the daisy chain network.
    We want to design our own product(PCB) inorder to achieve flexray to Optical fiber communication.
    Could you please help us for that topic?

    Regards,
    S.Saravanakumar

    Communication Architecture:

  • In reply to Saravanakumar S93:

    Alright, sounds like fun and will gladly lend a hand! Before continuing though could you specify what the four wire variant of Flexray is? As previously mentioned in my third post, I thought that it was just more data on a second bidirectional bus but it appears that it may be one diff pair for Tx and one for Rx, and not a second channel. Can you provide me information on this? I don't have access to the ISO standard and am only seeing two-wire online.

    Best Regards,
    Nick
  • In reply to Nicholas Mariani9:

    Hey Nicholas,
    Thank you very much for the quick feedback and support.
    The above architecture diagram shows the practical intended usage of our product.
    This is going to be used in Train Control systems.
    This is based up on optical fiber communication(Single mode).
    Even, we didnt have the ISO Standard. Sorry!!!.Since, there are limited informations are available for 4 wire.
    We can go with 2 wire flexray interface .

    Regards,
    S.Saravanakumar

  • In reply to Saravanakumar S93:

    Hey Saravanakumar,

    I've been looking into your request and have some comments and concerns. First, the topology you will need to be able to convert the 2 wire bidirectional is essentially what I had laid out in the "Two-Wire" post from earlier. The trouble will be the switching of the signals from Tx to Rx fiber. Based off of what I've read this is certainly possible but it requires knowledge of the Flexray frame, I'd recommend using the "TSS" bit as your switch indicator. You could do this by using a micro or some logic gates to match the wake up pulses and then scan for the TSS bit which enables the Tx when it is a logical "1". When no wake up is in place you can use the TSS but I would ensure you put a filter for the wake up sequence. I'll leave this bit of making the functional switching block to you.

    My concern with this plan is that the Flexray Consortium ceased in 2009 and the standard doesn't appear to be supported by any one body anymore. This could be a major issue for you since you are in the rail industry and they have systems that will hang around for a while once installed. If I was in your position I would strongly look into other options. One viable path would be to look into TTEthernet. It is a fault tolerant 100Meg Ethernet designed for high reliability. It appears to still be supported by the SAE, SAE AS6802, and is built for systems like yours. Additionally, it should allow for the embedding of Flexray data into its packets and will allow you to open the door for future system upgrades like CWDM for higher bandwidth throughput to allow the longest life out of your lines.

    If this answered your question please git the green verification button below; it's important to us to know that we could lend a hand in solving your problems! If you have more questions please feel free to send them my way and I will answer them to the best of my ability.

    Best Regards,
    Nick
  • In reply to Nicholas Mariani9:

    Hey Nicholas,
    Thank you for the detailed feedback and support.
    Based up on all your points, we will select the feasible and reliable solution.

    Regards,
    S.Saravanakumar

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