Currently I am working in AXI4 Stream protocol, I have an question what’s the necessity of Null_bytes in DATA stream. While transfer the data if there is a capability of null_bytes, null_bytes should be removed before received by destination. NUll_bytes doesn’t holds any information of data.
When null_bytes transfer occurs, in what scenario null_bytes is required.
Thanks,
Subashini J
In reply to Mobi.Subha:
Hi Subha,
When a byte stream of transfer is transmitted, then this transfer may consist of data and null bytes. Null bytes does not hold any information about the data nor the positional information of the data. Actually, it is added and removed by the interconnect when the TKEEP signal is deasserted by the master inorder to maintain a continuous chain of byte transfers.
So, The insertion of null bytes may be required for certain operations, such as upsizing to a wider data bus, where there are insufficient data and position bytes to make a complete data width transfer.(Refer SPEC chapter:2.3.2, pg:2-6)
EX: If master bus width is 32bits and slave bus width is 64bits, and a transaction requires 50bits of transmission from this master to slave, then during the first transfer 32 bits will be sent and the remaining 18bits(50-32=18) will be sent by adding additional 14 null bits(18+14=32). Hence transmitting 2 normal transfers.
Hi Dpksrini01,
I am attracted to your discussion. Can I use the Null byte to do the split joint for the Ethernet header 14bytes, and the 46bytes payload for the AXI4-S 64bits, and then will be a completed 60bytes transferred to the MAC to do FCS then transmitted ideally.
Thank you.