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Adventurer
Adventurer
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Registered: ‎02-18-2009

ARP by 10g/25g ethernet subsystem

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使用10g/25g ethernet subsystem收发包有最小包长64bytes的限制,而arp包的长度是小于这个限制的,如何使用这个ip收发arp包呢?

Theory is grey,
and only the tree of life forever!
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Explorer
Explorer
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Registered: ‎08-14-2013

Probably two main options - either generate the padding along with the rest of the frame, or write a small "shim" that sits right before the MAC and will pad all frames to 60 bytes.  I have one of these for the 512 bit AXI stream interface to the 100G CMAC core - it's very simple there as 512 bits means you have 64 byte lanes in each cycle, so padding is just a matter of masking tdata from tkeep and then setting the 60 LSBs of tkeep on the first cycle.  As the AXI stream interface on the 10G MAC is only 64 bits wide, some more state is required to extend the padding over 8 transfer cycles. 

Alternatively, you can use a different MAC that inserts the padding automatically. 

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Explorer
Explorer
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Registered: ‎08-14-2013

Pad the frames to 60 bytes (64 byte min length includes FCS, which the MAC will insert).  Or let the MAC do it for you, if it supports it.  On the receive side, simply ignore the padding bytes. 

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Adventurer
Adventurer
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Registered: ‎02-18-2009

how to pad the frame?

Theory is grey,
and only the tree of life forever!
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Highlighted
Explorer
Explorer
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Registered: ‎08-14-2013

Probably two main options - either generate the padding along with the rest of the frame, or write a small "shim" that sits right before the MAC and will pad all frames to 60 bytes.  I have one of these for the 512 bit AXI stream interface to the 100G CMAC core - it's very simple there as 512 bits means you have 64 byte lanes in each cycle, so padding is just a matter of masking tdata from tkeep and then setting the 60 LSBs of tkeep on the first cycle.  As the AXI stream interface on the 10G MAC is only 64 bits wide, some more state is required to extend the padding over 8 transfer cycles. 

Alternatively, you can use a different MAC that inserts the padding automatically. 

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Adventurer
Adventurer
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Registered: ‎02-18-2009

if the ARP is coming from PC...

Theory is grey,
and only the tree of life forever!
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Explorer
Explorer
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Registered: ‎08-14-2013

If it's coming from the PC, then your PC should pad it out to minimum length automatically.  Note that wireshark, tcpdump, and other software tools view transmit packets before they are handed off to the NIC driver - even if you see a short TX frame in wireshark, it's likely that it gets padded to the correct length either in the driver or in the NIC hardware. 

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