Update frame definition and acquisition counter definition

source/hw-spec/controller/channels/data_frames.rst

@@ -12,21 +12,21 @@ The frame format is:
 
 ::
 
-    uint32  Device_Address
-    uint64  Common_Timestamp
-    uint32  Sample_Size
-    var     Sample
+    uint32  dev_addr
+    uint64  acqclk_cnt
+    uint32  sample_sz
+    var     sample
 
 Where
 
-- ``Device_Address``: The address of the device producing the data, as featured
+- ``dev_addr``: Device Address. The address of the device producing the data, as featured
   on the :ref:`device table <dev-table>`.
-- ``Common_Timestamp``: A counter common to all devices generated by the
+- ``acqclk_cnt``: Acquisition counter. A counter common to all devices generated by the
   controller common acquisition clock. On write frames, this field is ignored.
-- ``Sample_Size``: The full size of the sample, and must be equal to the
-  ``Read_Sample_Size`` field of the :ref:`device descriptor <dev-desc>` on read
-  frames or a multiple of the ``Write_Sample_Size`` on write frames.
-- ``Sample``: The complete data sample as described on the :ref:`device sample
+- ``sample_sz``: Sample Size. The full size of the sample, and must be equal to the
+  ``rd_samp_size`` field of the :ref:`device descriptor <dev-desc>` on read
+  frames or a multiple of the ``wr_samp_size`` on write frames.
+- ``sample``: The complete data sample as described on the :ref:`device sample
   format <dev-sample>` section.
 
   While a read frame must always contain a single sample as generated by the devices, 

source/hw-spec/controller/index.rst

@@ -4,9 +4,26 @@ Controller
 ==========
 The :term:`controller`'s purpose is to interface an ONI hardware system with the host
 computer. It aggregates and routes device data and provides transparent access
-to all devices, independently of their physical location. The host also
-contains a common clock that is used to timestamp data from all devices,
-independently of their origin hub.
+to all devices, independently of their physical location. 
+
+.. _acq_clk:
+
+Acquisition Counter
+---------------------
+
+The controller MUST have access to a high resolution clock. The tick count from this
+clock is used to synchronize data from all devices independently of their origin hub.
+The controller MUST capture the counter value when receiving a :ref:`sample<dev-sample>`
+and use that value for the ``acqclk_cnt`` field of the corresponding :ref:`frame<frame>`.
+
+.. note:: The controller adds the acquisition counter when it receives the samples
+    and proceeds to create the associated frame. However, due to hub to controller
+    transmission delays, this time may have an offset from sample creation time.
+    To account for this, hubs contain a register indicating the measured
+    transmission delay. Users can use this value to more precisely synchronize
+    samples between hubs.
+
+.. todo::  update note admonition to links after the register map is updated
 
 .. _controller_params:
 
@@ -32,7 +49,7 @@ Communication
 
 .. toctree::
     :maxdepth: 1
-
+ 
     channels/index
     addresses
     register_interface