s2m_x4 kernel is generated from the
kernel/spec.json specification. Review this file again. Notice that the
s2m_x4 kernel has an implementation
StoreStreamToMaster which moves data from AXI-Streams to DDR. The
s2m_x4 kernel has 4 channels:
k3. Each stream writes the data coming from the
tx3 streams to a DDR buffer.