linux - Bridging ethernet traffic between two interfaces (USB-CDC ECM and Ethernet) using an mbed LPC1768 -

i'm working on project have lpc1768 mbed device. can connect device usb computer. device has working outgoing ethernet connection can read using mbed library.

on embedded device, internet traffic enters usb-cdc ecm protocol. want give packets working ethernet interface. have following code:

#include "mbed.h" #include "usbcdc_ecm.h" #include "rtos.h"  extern "c"{ #include <stdint.h> }  ethernet eth;  // create buffer #define eth_mtu 1514 static uint8_t buf[eth_mtu]; static char ethbuf[eth_mtu];  int main(void) {     usbcdc_ecm usb = usbcdc_ecm(0x0525, 0xa4a1, 1);      wait(1);      int rx_i = 0;      while(1)     {         int size = eth.receive();         if(size > 0)         {             eth.read(ethbuf, size);             printf("read ethernet: %d\r\n", size);              // send data usb             uint8_t *usb_data = (uint8_t *)malloc(sizeof(uint8_t) * size);             memcpy(ethbuf, usb_data, size);             int sent = 0;             while(sent < size)             {                 int to_send = 64;                 if ((size - sent) < to_send) { to_send = size - sent; }                 int res = usb.send(usb_data + sent, to_send);                 printf("result sending usb: %d\r\n", res);                 sent += to_send;             }             if ((size % 64) == 0) { usb.send(usb_data, 0); }         }          bool ret = usb.readep_nb(buf + rx_i, (uint32_t *)&size);         if(!ret) { continue; }          rx_i += size;         if(size < 64) {             printf("received frame size: %d\r\n", rx_i);              // send frame on ethernet             char *ethernet_data = (char *)malloc(sizeof(char) * rx_i);             memcpy(buf, ethernet_data, rx_i);             eth.write(ethernet_data, rx_i);             int result = eth.send();             printf("result: %d\r\n", result);              rx_i = 0;         }          wait(0.05);     } } 

so in each loop, read ethernet interface , pass these packages usb-cdc ecm (64 bytes @ time). next, read incoming traffic usb side , pass traffic ethernet interface.

this not working. i've used wireshark analyze traffic looks strange , packets seems corrupted. payload same. occurs traffic internet computer.

does know goes wrong here? pass packets other interface , don't modify them. below, i've added wireshark output.

it appears me memcpy() calls wrong way around.

void *memcpy(void *dest, const void *src, size_t n); 

destination first, source second argument.