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This page explains the content of an ARP packet, sent by the DUT.

1. The component responsible for sending ARP packet is the ethernet sender (MASSnd : ethernetSnd).
   First preamble and SFD are sent. Next comes the destination MAC address (low nibble first of the signal destinationMACLatch). The DEVICE_MAC follows. Then the DUT places the ethernet type field byte one and two: 0x08 and 0x06 (ARP). The entire ARP structure is shown in the following table: ARP frame structure
   The ARP data, that comes next, is read from the RAM. A higher layer prepared it.
   Some changes to the ETHERNET send component were required. This is explained in the next page . Some waveforms are shown too.


2. The higher layer ARP data preparation is done at the ARP send component (ARPSender : ARPSnd).
   Please refer to the VHDL code at (file name arpsnd.vhd ) and look for the following comment:
   -- create each byte of the ARP request according to cnt


3. The ARP send component, which initiated the ARP frame request, waits, at the mean time, for an ARP reply. The wait period is not forever of course. A timeout counter stops it and reports an error to an upper layer, shouldn't there be a reply arriving, within the allowed time interval. This is well explained in the code remarks within the VHDL code:
   
   if the reply doesn't come back, then inform the above layer that the frame was sent. Assume the higher level protocol can account for this problem, or possibly an error signal could be created once a higher level protocol has been written that can accomodate this if ARPCntOverflow = '1' then ...
   


4. Optionally (if(enable_record...) the ARP packet can be printed from the test-bench. vhdl ARP print


5. When ARP reply is correctly received, the ARP table is updated. The content of the ARP reply and waveform is in the next link.

To go back to the transmit page: TX .
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Home	Download Area FCS c code for calculating CRC for ETHERNET