diff --git a/piker/fsp/_engine.py b/piker/fsp/_engine.py
index 93bf0388..78448d01 100644
--- a/piker/fsp/_engine.py
+++ b/piker/fsp/_engine.py
@@ -39,7 +39,10 @@ from ..data.feed import (
     Feed,
 )
 from ..data._sharedmem import ShmArray
-from ..data._sampling import _default_delay_s
+from ..data._sampling import (
+    _default_delay_s,
+    open_sample_stream,
+)
 from ..data._source import Symbol
 from ._api import (
     Fsp,
@@ -336,7 +339,6 @@ async def cascade(
         symbol = flume.symbol
         assert src.token == flume.rt_shm.token
         profiler(f'{func}: feed up')
-        # last_len = new_len = len(src.array)
 
         func_name = func.__name__
         async with (
@@ -442,22 +444,21 @@ async def cascade(
                 # signal
                 times = src.array['time']
                 if len(times) > 1:
-                    delay_s = times[-1] - times[times != times[-1]][-1]
+                    delay_s = float(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.
-                async with flume.index_stream(
-                    int(delay_s)
-                ) as istream:
+                # sub and increment the underlying shared memory buffer
+                # on every step msg received from the global `samplerd`
+                # service.
+                async with open_sample_stream(float(delay_s)) as istream:
 
                     profiler(f'{func_name}: sample stream up')
                     profiler.finish()
 
                     async for i in istream:
-                        # print(f'FSP incrementing {i}')
+                        print(f'FSP incrementing {i}')
 
                         # respawn the compute task if the source
                         # array has been updated such that we compute