.. _onidatasheet_loadtest:

Load Test Device
###########################################
:Authors: Jonathan P. Newman
:Version: 1
:IO: Frame Source, Register Access
:ONIX ID: 27
:ONIX Hubs: This device is used for real-world bandwidth and latency testing.

Description
*******************************************
The **Load Test** device that produces data at user-settable size and rate to
stress test various communication links and test closed-loop response latency.

.. _onidatasheet_loadtest_reg:

Register Programming
*******************************************

.. list-table::
    :widths: auto
    :header-rows: 1

    * - Address
      - Name
      - Access
      - Time of Effect
      - POR Value
      - Reset Action
      - Description

    * - 0x00
      - ENABLE
      - R/W
      - On Reset
      - Implementation dependent, see hub documentation
      - None
      - The LSB is used to enable or disable the device data stream:

        * 0x0: data output disabled
        * 0x1: data output enabled

    * - 0x01
      - CLK_DIV
      - R/W
      - On Reset
      - CLK_HZ / HB_HZ where HB_HZ is a implementation dependent default rate
      - None
      - Heartbeat clock divider ratio. Minimum value is CLK_HZ / 10e6

    * - 0x02
      - CLK_HZ
      - R
      - N/A
      - N/A
      - None
      - The frequency parameter, CLK_HZ, used in the calculation of CLK_DIV.

    * - 0x03
      - DT0H16_WORDS
      - R/W
      - On Reset
      - 0
      - None
      - The number of incrementing 16-bit integers sent in each frame. 

        .. note:: 
            The maximum value of DT0H16_WORDS depends of CLK_HZ and
            CLK_DIV. There needs to be enough clock cycles to satisfy

            .. math::

                DT0H16\_WORDS <= CLK\_HZ / CLK\_DIV - 9 

            Setting DTOH16_WORDS above this value will result in a *decreased*
            device to host load as samples will be skipped.

    * - 0x04
      - HTOD32_WORDS
      - R/W
      - On Reset
      - 0
      - None
      - The number of 32-bit word dummy data in in each Host To Device frame.
        Write frames always start with a single 64-bit unsisigned integer,
        which is looped subtracted from the Hub Clock Counter when it is
        received to produce a Hub Clock Delta that is looped back into the
        device to host data frame for testing loop latency. All other data is
        ingored.

.. _onidatasheet_loadtest_d2h:

Device To Host Data Frames
******************************************
With DT0H16_WORDS = 4, each frame transmitted to the host is structured as
follows:

.. wavedrom::

    {
        reg: [
          {bits: 64, name: "Acquisition Clock Counter", type: 0},
          {bits: 32, name: "Device Address", type: 0},
          {bits: 32, name: "Data Size", type: 0, attr: 24},

          {bits: 64, name: "Hub Clock Counter", type: 3},

          {bits: 64, name: "Hub Clock Delta", type: 5},

          {bits: 16, name: "Frame Word 0", type: 6, atter:42},
          {bits: 16, name: "Frame Word 1", type: 6, atter:43},
          {bits: 16, name: "Frame Word 2", type: 6, atter:44},
          {bits: 16, name: "Frame Word 3", type: 6, atter:45}

        ],
        config: {bits: 320, lanes: 10, vflip: true, hflip: true, fontsize: 11}
    }

|

    Hub Clock Counter Delta
      64-bit unsigned integer that the result of subtracting the Hub Clock
      Counter value from the Hub Clock Counter Loop back value in
      :ref:`onidatasheet_loadtest_h2d`. This provides a real-world, hardware
      timed measurement of closed-loop latency.

    Frame Word N
      Ignored data that can be used for host to device load testing.  When
      DT0H16_WORDS is set to a different value, the Data Size field along with
      the number of words at the end of the frame will change.

.. _onidatasheet_loadtest_h2d:

Host To Device Data Frames
******************************************
With HTOD32_WORDS = 2, each frame transmitted to the host is structured as
follows:

.. wavedrom::

    {
        reg: [
          {bits: 32, name: "Device Address", type: 0},
          {bits: 32, name: "Data Size", type: 0, attr: 16},

          {bits: 64, name: "Hub Clock Counter Loopback", type: 3},

          {bits: 32, name: "Frame Word 0", type: 6, atter:42},
          {bits: 32, name: "Frame Word 1", type: 6, atter:43},

        ],
        config: {bits: 192, lanes: 6, vflip: true, hflip: true, fontsize: 11}
    }

|

    Hub Clock Counter Loopback
      64-bit unsigned integer that is subtracted from the current Hub Clock
      Counter value to produce the Hub Clock Counter Delta field in
      :ref:`onidatasheet_bno055_d2h`.

    Frame Word N
      Ignored data that can be used for host to device load testing.