The objective of the mapper is to prevent buffer conflicts, where possible. It
also has different buffer optimization levels that try to bloat or increase the size of
buffers to prevent conflicts. These buffer optimization levels range from 0 (default) to
9. They are invoked with the Xmapper option, --Xmapper=BufferOptLevel<level num>. At the highest buffer
optimization level (9), no two buffers can be placed in the same bank. However it is
important to know that at the higher buffer optimization levels it might become
impossible for the mapper to find a solution and it will error out. So the first option
if you see a large number of memory stalls is to cycle through the BufferOptLevel options to see if fewer memory stalls are
seen at higher bufferOptLevels.
Another possibility is that you can explicitly inform the mapper not to place
two buffers in the same bank. If your simulation analysis indicates that a significant
throughput degradation is caused by memory stall resulting from a bank conflict between
buffer kernel_0.in[0] and kernel_1.out[0], you can provide a directive to the mapper to not place
these buffers in the same bank as follows.
not_equal(location<buffer>(kernel_0.in[0]), location<buffer>(kernel_1.out[0]));Xrouter option DMAFIFOsInFreeBankOnly can force the router to place these
FIFOs in free banks. This eliminates memory conflicts with the DMA FIFOs. If it is not
possible to reserve an entire free bank for the DMA FIFO then location constraints can
be used in coordination with outside knowledge of memory buffers. In this case it is
important to have knowledge of which buffers might cause stalls when conflicting with
DMA FIFOs. The constraints can look like the
following.location<fifo>(net2) = { dma_fifo(aie_tile, 15, 0, 0x3100, 32) };