I have a problem trying to connect with Rabbit RCM6700 using Exar XR22801 through USB connection. Exar XR22801 acts as a bridge with a switch and with a GPS module connected to one UART line, all in one PCB. In principle, the USB-Ethernet driver works well with most connected devices but I am having trouble establishing a connection with the Digi Rabbit RCM6700 microprocessor. When connecting the RCM6700 device to the switch via Ethernet, from the USB interface I can connect to the device only if I deactivate the option "TCP Checksum Offload" or activate the option "only for Tx" on the driver. The problem is that by doing this, the network connected to the switch of our equipment goes much slower.
The configuration of the driver also has auto 100 MB full duplex and flow control disabled. I have tried to activate / deactivate all the options of the driver and I only get the connection by deactivating "TCP Checksum Offload". Some tests performed:
- Using a normal Ethernet connection with the Rabbit RCM6700 microprocessor everything works correctly without deactivating the checksum offload options.
- Using another microprocessor (ECOG1X14Z5 MCU) everything works correctly using the USB interface, without deactivating "TCP Checksum Offload".
- Using wireshark to capture the packets of the TCP connection, it seems that the SYN ACK packets that the microprocessor RCM6700 should send to the PC are lost, so that connection is not reached. With normal Ethernet interfaces this does not happen.
- Operating system windows 7/8/10 (tested on all three).
- Software version Dynamic 10.72.
- Ethernet connection with fixed IP on all devices, all in the same subnet.
- The PCB switch has two RJ45 Ethernet interfaces and the interface with the Exar device. Making the connection using only the RJ45 connections everything works fine, it is only when the microprocessor is connected through the RJ45 port and an attempt is made to connect through the USB port.
It is probably a problem of compatibility between the two devices but I would like to know what else I can do.
Thanks in advance and greetings.