Hi,
I saw from the dustsheet of your board that you have a Marvell Alaska PHY who supports GMII and MII interface, I will talk about MII just because I am more familiar.
U can set/read your PHY status via the pins MDC (clk) and MDIO (data input and output). This is a quite common interface for this kind of devices, you must read and write into registers to set parameters.
Remember that, in general there is an "active low" RST pin (and so you must set it high to activate the PHY).
You can set the speed, the auto-negotiation, ... of the link and I suppose you set 100MBit/s, MII, autonegotiation enabled.
Once you have done this, the 2 PHYs (computer and board) are automatically keeping the link alive (sending sometimes a little packet), you can see this because the status of the computer network interface changes to connected (most probably you can read "Unknown net").
Now you are pretty ready to send and receive bits!!!
You can read the data send by the computer when the DV pin is set to 1, in the same way, to transmit your data you must set the TX_EN pin to 1.
In the MII mode the CLKs are 25MHZ and on every rising_edge you must read/write 4 bits (also called 1 nibble) per clk cycle on the RX(3 downto 0) and TX(3 downto 0);
For every byte you must send the less significant nibble first, so, if you want to send the value 16 (0x10), you will send:
0 0 0 0 (first clk cycle)
0 0 0 1 (second clk cycle)
If you have 2 boards, you can start sending simple data from one board to another to get familiar with this staff.
Now you must send something that the PC can understand....
Install wireshark (it is a sniffer) and remember:
On an Ethernet cable are running MAC frames.
A MAC frame can contain an IP packet.
An IP packet can contain TCP or UDP datagrams. (I suggest you to use UDP since it is much more simple)
You can find all the structure of frames,packets and datagrams on internet, just google it.
A couple of tricks
1) In general wireshark is showing you all the frame received WITHOUT: PREAMBLE, SFD and FCS (crc).
That appens because this is all the MAC level is passing to WIRESHARK.
If you want to check your crc you can append to your frame 4 Bytes of garbage (no matter what) so that the MAC
erases them but is letting the CRC pass.
2)If you want to send packets all of the same size, to the same IP address, the IP checksum is constant and you can
calculate it just once (even pen and paper are enough) avoiding to add extra logic on your project.
3)You can find VHDL codes for calculating the CRC (try this link:
http://www.electronicdesignworks.com/utilities/crc_generator/crc_generator.htm)
If you need further information ask.
Fabrizio
