Explicit latency constraint between two stream objects which accesses to external resources outside of the stream.

[shtaxxx]

thread.stream has some external operators to access outside of the stream pipeline, such as ToExtern/FromExtern, read_RAM, write_RAM. Additionally, RingBuffer and Scratchpad uses on-chip RAM as a random access buffer.

The result of such the external operators are sensitive to their read/write timings. So scheduler has to support the explicit latency constants between two (or more) linked external operators.

[shtaxxx]

This issue is not resolved yet, but the same thing can be realized by using Substream.