Telestra 3 App Note

Running Telestra 3 MBV Platform at a Lower Frame Rate (#80)

Introduction

The Telestra 3 Model Builder Visual (MBV) platform is a powerful and comprehensive communications and audio development & runtime environment. MBV runs at a default frame rate (aka tick rate) of 1000 Hz and audio sample rate of 48 KHz. This default setting provides the most comprehensive performance available in the marketplace today. However, given the current CPU loading rates there are certain circumstances where an individual communication model is too large to fit on a single platform. While spreading the model across two platforms is always an option, there is an additional configuration available that allows a single Telestra platform to handle a greater load.

To achieve this, the frame rate and audio sample rates are reduced in the interest of reducing the CPU loading; however, this is done at the expense of audio quality and audio response time. The frame rate delta from 1000 Hz to 500 Hz is usually not detectable by the end user, but the side-effect is doubling the time needed for audio to traverse from an input to an output in the model. The sample rate of 16 KHz is definitively a reduction in audio fidelity from a rate of 48 KHz. However, if these trade-offs are acceptable and you have a model that is pushing the edge of the CPU, then running at the lower frame rate may be a good option for your application. In general, when a model CPU load is greater than 65% (as shown in RMS) it is starting to reach the maximum performance level of that platform's CPU and is a candidate for the lower frame rate or possibly a hardware upgrade. Contact ASTi for details on hardware upgrade options.

Software Requirements

ASTi Software Version 3.30-1 or later

Hardware Requirements

No hardware changes are required. A power cycle of all equipment is necessary after configuration files are changed.

Configuration of Telestra for Running at Lower Rate

There are two files that must be changed to run at the lower frame rate. Both files must be changed; you cannot modify one and not the other.


Step 1: Changing the frame rate from 1000 Hz to 500 Hz

Login as root or su to root. At the prompt execute the following:

echo "500" > /usr/local/asti/etc/arate

This creates a file named arate which contains the text "500". This will change the realtime frame rate on the Telestra.


Step 2: Changing the audio rate 48 KHz to 16 KHz

Note: The audio rate is defined in the model, so you will have to follow this procedure for every model you wish to run at 16 KHz. After you modify, edit, or save each model, the new audio rate will remain at 16 KHz.

Login as root or su to root. At the prompt execute the following:

cd /home/<username>/.mbv/<modelname>

<username> is the system user account (i.e. development account) where the model resides. If the model is in the embedded account the <username>=mbvuser.

<modelname> is the name of the model you are going to run at 16 KHz.

echo "16000" > .srate

This creates a file named .srate containing the text "16000" which will change the audio rate to 16 KHz on a per model basis. If you have more than one model that is required to run at 16KHz repeat this procedure. Pay special attention to the "Embedded" user's models (in /home/mbvuser/.mbv/). If you accidentally load a model with the default 48KHz sample rate on a Telestra with a 500Hz realtime, the system will not run and may crash.


Step 3: Power cycle all equipment
  1. Power down the Telestra
  2. Power down all USB devices (Iris, Axis, Prism, and Spectrum)
  3. Wait 120 seconds
  4. Power on all USB devices
  5. Power on the Telestra

The model and Telestra platform are now configured to run at the lower frame rate.


Limitations

The Hardware Readiness Test (via RMS) is not supported at the reduced frame rate.