Save the valid AXI beats number of the last AXI transaction, and the valid
DMA beats number of the last AXI beat, so the read back logic can use this
data and prevent to feel up the CDC memory with invalid samples. Also in
this way the end of the read back cycle get a more robust control: no more
duplicated samples at the end of the buffer.
Update the readback logic of the FIFO. The controller uses a
relative address counter, which counts the DMA beats. The readback
logic uses the last value of that counter to define the wrapping
address. The aditional data from the last AXI burst, if there is any,
will be dropped.
Istvan Csomortani