CANopen performance

We are having problems with failures when attempting relatively rapid CANopen write requests. The initial estimate for the system assumed that four 1 Mbit CANbuses would support 80 writes at 50 Hz. In theory it looks easy, looking at bandwidth (assumed 50 bits per frame, gives 50 kbit/s per CANbus).

The question is basic, but probably not easy to answer: is it reasonable to expect to do 20 writes at 50 Hz = 1000 writes per second on each CANbus using CANopen? The web-page

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has made me wonder whether the answer is no (it mentions 2-3 ms CANopen overhead per cycle),


Philip Taylor

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What do you mean by write requests ? A PDO or SDO ? A write from master to slave or message transmission from slave to master ? If this is a PDO, which mode are you using ?

In the simplest case, the PDO transfer does not add any run time overhead compared to a simple CANbus broadcast.

What kind of controller chips (Philips vs. Intel) are used at the CanOpen master resp. slave ?

Those figures sounds like SDO transaction times on a low speed bus:-).

If this is really PDO overhead, the only explanation for this kind of overhead would be some intelligent CanOpen cards with an own processor that needs some handshaking with the main processor.


Reply to
Paul Keinanen

That article refers to the time from signal input to the slave, processing at the master and outputting an other signal on the same or different slave. It also assumes 1-2 ms processing latency at the master after a "frame received" interrupt.

While this is the worst case two way delay, in a typical environment, multiple slaves transmit their measurements simultaneously (arbitrated by the hardware), multiple signals are processed at once in the master and multiple output frames are sent from the master immediately after each other. Thus, there is quite a lot overlapping input-processing- output transactions and thus, the bus can be highly utilised.


Reply to
Paul Keinanen

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