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I use an industrial PC from Siemens 427d IPC kind, based on an Intel 1.6Ghz processor i3-3217UE, QM77 Express Chipset with an "Ethernet Phy 82579LM" and another component 82574L Ethernet.
I want try to use an Ethernet port as EtherCAT master, which requires Fast Ethernet bidirectional @100mbps . I have one cyclic frame to transmit with 1000 bytes all 250US and to receive as return one frame of the same size in the network, the frame should be returned to RAM before the next cycle EtherCAT. I can run this using the 82574 Ethernet component but it does not work with the 82579. I tried to understand why. So I measured the time between when the driver gives the order to send and when I detect the frame start on the element connected by Ethernet. I see that time is 86,7us for 82579 and 10us for 82574 This time is used by the DMA transfer and the start of sending data through the Ethernet component If 10us sounds reasonable, 80us is not. By consulting the documentation of 82579 component and chipset, I have not found registry to increase the speed of DMA transfer or to decrease this time. As it is a component working 1Gbps, it must be able to work faster. I have not measured the time of the return of frame information in RAM, but with a time of 86 us for the transmission of data and 86,7us for the transfer memory-> transmission start and if I suppose same time for the end of the frame transfer received-> Memory, I am very close to my 250US. Do you have a way to reduce the transfer time for a 100mbps connection for 82579LM component? A 1Gbps it seems much shorter and I would say better than the 82541.