More about AXI - muneeb-mbytes/axi4_avip GitHub Wiki

Difference between transfer and transaction

Transaction contains transfers. Transaction is the whole burst in which number of transfers with individual data with their own address with respect to burst type are being carried out.

Can write and read happen in the same location at the same clock cycle

it might be a bit confusing for compiler to tell so it is left to the implementation. if write and read happens at the same location we cannot predict which happens first but if the write transfer finishes due to less clock cycles then it is not a problem but if happens within same time then we may read a empty data.so it is left upto the implementation of protocol.

How fixed burst used in FIFO

In FIXED type of burst the memory location used to make transaction remains same,herecomes the question if our memory is capable of storing only 32 bit data in each of 32 bit address locations then how can a burst transfer occurs.FIFOs are meant of storing data and retrieving in first in first out manner.in fixed bursts the address remains same that fetches a FIFO peripheral continuously.

why WID is removed in AXI4

AXI4 removes support for write data interleaving. In AXI4, all of the write data for a transaction must be provided in consecutive transfers on the write data channel in the order in which write address transfers are sent.
With write data interleaving, a slave interface can accept interleaved write data with different AWID values. The write data interleaving depth is the number of addresses for which a slave can accept interleaved data. When accessing a slave that supports write data interleaving, write data from different transactions that use the same AWID cannot be interleaved.

4KB boundary..why?

In AXI 4KB boundary is the restriction of a transfer whose memory access exceeds the partitioned 4096 Bytes boundary. means the memory will be divided into few parts of 4KB like 0 to 4095 and 4096 to 8191 and so on.Here 4095,8191... are the 4KB boundaries.

• Wherever the transaction may start but once it reaches it's 4KB boundary then the transaction is not carried forward or else should start again at a new location.
• Why the 4KB boundary means the main memory that is RAM of a AXI protocol implemented is capable of capturing 4KB pages only for any read or write transaction.
• But the page size is not limited anywhere based on the architecture ,manufacturing space, cost and hardware it may be changed but not in AXI protocol.