Rapid prototyping of DSP algorithmsRapid prototyping of DSP algorithmsRapid prototyping of DSP algorithms

Mattias Arlbrant

real-time

Grupphandledare, ANC

Agenda Agenda

1. Our DSP system1. Our DSP system

2. Creating a Simulink model2. Creating a Simulink model

3. Running the Simulink model on our C6713 signal processor

3. Running the Simulink model on our C6713 signal processor

4. Changing parameters in the signal processor in real-time

4. Changing parameters in the signal processor in real-time

5. Measuring performance5. Measuring performance

In Active Noise Controlprocessing latency (=time delay) is critical!

Longer delay Lower performance

t

Timet-1t-2t-3 t+1 t+2 t+3 t+4t-4

= acoustic delay + processing delay

Prediction

Depends on distance betw. loudspeaker and mic

Depends on our signal processing system

Processing TimeProcessing TimeWaiting Waiting

TimeTime

Sample TimeSample Time(= 0.125ms @ 8kHz, sound travels ~ (= 0.125ms @ 8kHz, sound travels ~ 0.000125*340=4.25cm during that time)0.000125*340=4.25cm during that time) ‏‏

nn n+1n+1

RealReal--time time processing processing

We can say we have a real-time application if the CPU can do all processing in the time between two samples.

Note that we also have to take care not to introduce extra delay in the algorithms, like for example by using block processing

DSPs DSPs

-

Special instructions for common signal processing tasks

- Cheap

-

Low power consumption

= Digital Signal Processors, special CPUs for signal processing

Characteristics of DSPs:Characteristics of DSPs:

Our feedback ANC systemOur feedback ANC system

DSP board with AD/DA

AmplifierMic

USB cable

No more noise! Let's cancel it all!

PCAwful noise!

The Texas Instruments C6713 DSK boardThe Texas Instruments C6713 DSK board-

225 MHz TMS320C6713 floating point DSP

-

16 MB Dynamic RAM , 512 kB Flash memory

-

USB interface, 4 DIP switches, 4 LEDs

-

AD/DA with 8-96kHz sampling frequency

Automatic DSP code generationAutomatic DSP code generation

Simulink/MATLABSimulink/MATLAB

CCS (Code Composer Studio) CCS (Code Composer Studio)‏ ‏

TI C6713 DSK boardTI C6713 DSK board

Clever DSP engineer

Simulink generates C-code from a “model”

at the press of a button!

CCS does compiling, linking and downloads executable to the DSP!

The user only has to create a Simulink “model”

and press a button!

(That could be you!) ‏

= “Target”

Modeling in SimulinkModeling in SimulinkCreating a new Simulink model

Click the “Simulink”

button in MATLAB to open an empty model

Click the “Simulink”

button in MATLAB to open an empty model

Adding blocks from the Simulink Library BrowserModeling in SimulinkModeling in Simulink

Drag and drop

Connecting the blocksModeling in SimulinkModeling in Simulink

Signals, can be -

Sample-based = one sample at a time-

Frame-based = a block of samples at a time-

Multi-channel = two or more frame/sample basedsignals

Changing block propertiesModeling in SimulinkModeling in Simulink

Type

Coefficients

Double-clicking on a block opens a parameter dialog:

Ex. Digital Filter:

Simulation in SimulinkSimulation in Simulink

Start buttonSimulation time

Simulation in SimulinkSimulation in Simulink

Add a “Target preferences”

block

...to let Simulink know what to generate C code for!

Simulink Simulink ––

generating DSP code generating DSP code

Add A/D and D/A blocksSimulink Simulink ––

generating DSP code generating DSP code

Simulink Simulink ––

generating DSP code generating DSP code Check AD/DA settings: smpl per frame, fs etc.

Press the magic button...Simulink Simulink ––

generating DSP code generating DSP code

CCS opens automatically... and connects to the DSP

Run / stop buttons

Simulink Simulink ––

generating DSP code generating DSP code

RTDX RTDX ––

RealReal--Time Data ExchangeTime Data ExchangeTo communicate with the DSP while it is running

RTDX Channels (via USB) ‏

GUI (=Graphical User Interface) designed in MATLAB

C6713 DSK

RTDX RTDX ––

RealReal--Time Data ExchangeTime Data ExchangeEx. : Add an RTDX block to control the output level

Name of channel

Enable

RTDX RTDX ––

RealReal--Time Data ExchangeTime Data ExchangeSet RTDX data in the MATLAB GUI

Channel name

Select DSP/BIOS –

CPU Load Graph

Performance Performance ––

CPU LoadCPU Load

Performance Performance --

LatencyLatency

We can measure the delay that our DSP board introduces by comparing impulse response measurements on two channels:

RME soundcardOut In

PC with MATLAB

Performance Performance --

AliasingAliasing

-

Make sure you use efficient decimation and interpolation filters when you process at a lower sample rate

-

Non-linearities like aliasing components in the feedback loop can cause instability

-

Check with sinusoids that the aliasing is kept at a low level

Important advice!Important advice!

Build your Simulink model one step at Build your Simulink model one step at a time and test it after EVERY step!a time and test it after EVERY step!

Good luck!

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Help>Link for CCS>Automation Interface>Getting started with RTDXRTDX

Resources and tipsResources and tipsResources and tips

Simulink

MATLAB GUI

-

MATLAB GUI prototype implementing RTDX communication (available on course web site) ‏

-

Type “guide”

in MATLAB, opens a nice GUI editor

http://www.mathworks.com/demos/getting_started_with_simulink_demo_video.html

- Help>Simulink

-

Help>MATLAB>Creating graphical user interfaces

-

MATLAB GUI prototype implementing RTDX communication (available on course web site)‏

Useful Simulink blocksUseful Simulink blocksUseful Simulink blocks

The “Subsystem”

block –

use it to make the model less cluttered

“Delay line”

and “Matrix multiply”

–

to implement your own filters

“Mux”

and “Demux”

–

to join and split vector signals

“Transpose”

-

to transpose vector signals

“Scope”

, “Spectrum scope”, “To workspace”

-

to inspect signals

“FIR Decimation/Interpolation”

or “Digital filter”

and “Upsample/Downsample”

-

to do processing at a lower sample rate

Simulink pitfallsSimulink pitfallsSimulink pitfalls

The “Delay line”

block –

make sure you set “Allow direct feedthrough”correctly

The “Delay line”

block –

the output column vectors have the least delayed sample at the bottom

Make sure there is at least one sample of delay in feedback loops