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Is during AXI unaligned transfer not all WDATA bits used?

Dear Forum,

Can you please confirm one thing.

When we have un-aligned transfer, do some of WDATA bits not used during that transfer?

For example, in the below unaligned transfer WDATA[7:0] are not used for the 1st transfer. Is my understanding right?

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  • Yes, your understanding is correct. The unaligned start address of 0x01 immediately tells you that data for address 0x0 is not being transferred, so nothing will be transferred on WDATA[7:0].

    For INCREMENTING type bursts it is only this first transfer in the burst that doesn't use WDATA[7:0] as you see in the spec diagram, but for FIXED burst types the address remains constant for each transfer in the burst, so WDATA[7:0] wouldn't be used for any of the transfers,

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  • Yes, your understanding is correct. The unaligned start address of 0x01 immediately tells you that data for address 0x0 is not being transferred, so nothing will be transferred on WDATA[7:0].

    For INCREMENTING type bursts it is only this first transfer in the burst that doesn't use WDATA[7:0] as you see in the spec diagram, but for FIXED burst types the address remains constant for each transfer in the burst, so WDATA[7:0] wouldn't be used for any of the transfers,

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