tcDspFpgaIir

Introduction

The tcDspFpgaIir class may be used to provide access to a single IIR Filter core. Each instance of DspFpgaIir provides access to up to 4 individual filters. These filters are arranged in 1-4 parallel paths. The number of paths (NP) is application-specific. The number of filters (NF) cascaded along each path is configurable, as follows:

• NP=1, NF=1-4
• NP=2, NF=1-2
• NP=3, NF=1
• NP=4, NF=1

Each filter makes use of 5 coefficients (B0, B1, B2, A1, and A2) as described below:

/// Xin --->+---->(xB0)---->(+)---->(+)-------------->+---> Yout
///         |                ^       ^                |
///        Z-1               |       |               Z-1
///         |                |       |                |
///         +---->(xB1)---->(+)     (+)<----(xA1)<----+
///         |                ^       ^                |
///        Z-1               |       |               Z-1
///         |                |       |                |
///         +---->(xB2)------+       +------(xA2)<----+
/// 

There is no limit to the number of instances of tcDspFpgaIir that may be created, aside from the design of the FPGA module.

See also:

MityDSP::tcDspFpgaIir Class Reference

Example

This is a simple example of tcDspFpgaIir creation and usage:

 {
     unsigned int  my_base_addr = 0xB0000180;
     tcDspAwg     *myIir;
     int           numPaths, numFilters;
     int           B0, B1, B2, A1, A2;
     float         fB0, fB1, fB2, fA1, fA2;

     // create an IIR interface
     myIir = new tcDspFpgaIir((void *)my_base_addr);

     // determine paths available
     numPaths = myIir->GetPaths();

     // attempt to set two cascaded filters per set
     if (myIir->SetFilters(2) == false)
     {
         // failed... number of paths must not be what app expected
         printf("Couldn't set NF to 2, NP is %1d\r\n", numPaths);
         return;
     }

     // set all filter coes (pass-thru in this simple example)
     B0 = tcDspFpgaIir::gnCoeffScale;
     B1 = B2 = A1 = A2 = 0;
     myIir->SetCoeffs(0, 0, B0, B1, B2, A1, A2);
     myIir->SetCoeffs(0, 1, B0, B1, B2, A1, A2);

     // can also pass coes as floating point (-2 < x < 2)
     fB0 = 1.0f;
     fB1 = fB2 = fA1 = fA2 = 0.0f;
     myIir->SetCoeffs(1, 0, fB0, fB1, fB2, fA1, fA2);
     myIir->SetCoeffs(1, 1, fB0, fB1, fB2, fA1, fA2);

     ...
 }