read a received packet from the Ethernet buffers and send it to the lwIP for handling

To read a received packet from the Ethernet buffers and send it to lwIP for handling, you need to follow these steps:

1. Retrieve the packet from the Ethernet buffers. This can typically be done using DMA (Direct Memory Access) to transfer the packet from the Ethernet controller's buffer to a buffer in memory.

2. Check the packet header to determine whether it is an IP packet or not. If it is not an IP packet, you can discard it.

3. If the packet is an IP packet, pass it to lwIP for handling by calling the appropriate function. This function will typically be something like `ethernet_input()` or `ip_input()`, depending on the specific implementation.

4. Once the packet has been passed to lwIP, it will handle it according to its configured networking stack. This may involve routing the packet to its destination, processing any network protocols that are encapsulated within the packet, or performing other operations as needed.

5. After lwIP has finished handling the packet, it may generate a response packet that needs to be transmitted back out onto the network. To do this, you will need to use the Ethernet controller's transmit buffer to send the packet back out onto the network.

Overall, the process of reading a received packet from the Ethernet buffers and sending it to lwIP for handling can be complex, and will depend on the specific implementation of lwIP and the Ethernet controller being used. However, by following the general steps outlined above, you can begin to understand the basic flow of data through the networking stack.