"TMS320C55x DSP Library DSPLIB Programmer's Reference"

iircas51This function retains the address of the delay filter memory d containing theprevious delayed values to allow consecutive processing of blocks. This functionis more efficient for block-by-block filter implementation due to the C-callingoverhead. However, it can be used for sample-by-sample filtering (nx = 1).The usage of 5 coefficients instead of 4 facilitates the design of filters with aunit gain of less than 1 (for overflow avoidance), typically achieved by filtercoefficient scaling.Algorithm(for biquad)d(n) x(n) a1*d(n 1) a2*d(n 2)y(n) b0*d(n) b1*d(n 1) b2*d(n 2)Overflow Handling MethodologyNo scaling implemented for overflow prevention.Special Requirements noneImplementation Notes noneExampleBenchmarksSee examples/iircas5 subdirectory(preliminary)Cycles † Core: nx * (5 + 5 * nbiq)Overhead: 60Code size(in bytes)126† Assumes all data is in on-chip dual-access RAM and that there is no bus conflict due to twiddletable reads and instruction fetches (provided linker command file reflects those conditions).iircas51FunctionCascaded IIR Direct Form I (5 Coefficients per Biquad)ushort oflag = iircas51 (DATA *x, DATA *h, DATA *r, DATA *dbuffer, ushort nbiq,ushort nx)(defined in iircas51.asm)Argumentsx [nx]h[5*nbiq]Pointer to input data vector of size nxPointer to filter coefficient vector with the followingformat:h = b01 b11 b21 a11 a21 ....b0i b1i b2i a1i a2Iwhere i is the biquad index (a21 is the a2 coefficient ofbiquad 1). Pole (recursive) coefficients = a. Zero(non-recursive) coefficients = bFunction Descriptions4-59