Always load FSPs with the default (fast) sampling period

piker/fsp/_engine.py

@@ -37,6 +37,7 @@ from .. import data
 from ..data import attach_shm_array
 from ..data.feed import Feed
 from ..data._sharedmem import ShmArray
+from ..data._sampling import _default_delay_s
 from ..data._source import Symbol
 from ._api import (
     Fsp,
@@ -105,7 +106,7 @@ async def fsp_compute(
         filter_quotes_by_sym(fqsn, quote_stream),
 
         # XXX: currently the ``ohlcv`` arg
-        feed.shm,
+        feed.rt_shm,
     )
 
     # Conduct a single iteration of fsp with historical bars input
@@ -313,7 +314,7 @@ async def cascade(
 
         profiler(f'{func}: feed up')
 
-        assert src.token == feed.shm.token
+        assert src.token == feed.rt_shm.token
         # last_len = new_len = len(src.array)
 
         func_name = func.__name__
@@ -420,7 +421,11 @@ async def cascade(
                 # detect sample period step for subscription to increment
                 # signal
                 times = src.array['time']
-                delay_s = times[-1] - times[times != times[-1]][-1]
+                if len(times) > 1:
+                    delay_s = times[-1] - times[times != times[-1]][-1]
+                else:
+                    # our default "HFT" sample rate.
+                    delay_s = _default_delay_s
 
                 # Increment the underlying shared memory buffer on every
                 # "increment" msg received from the underlying data feed.
@@ -431,7 +436,8 @@ async def cascade(
                     profiler(f'{func_name}: sample stream up')
                     profiler.finish()
 
-                    async for _ in istream:
+                    async for i in istream:
+                        # log.runtime(f'FSP incrementing {i}')
 
                         # respawn the compute task if the source
                         # array has been updated such that we compute