/*******************************************************************************
Copyright(c) 2000 - 2003 Analog Devices. All Rights Reserved.
Developed by Blackfin DSP software Group, IPDC, Bangalore, India
for Blackfin DSPs.
By using this module you agree to the terms of the Analog Devices License
Agreement for DSP Software. 
********************************************************************************

Module name     :   fir_fr24.asm
Label name      :   __fir_fr24
Version         :   1.1

Change History  :
                Version     Date        Author          Comments
                1.1         02/17/2003  Swarnalatha     Tested with
                                                        VDSP++ 3.0 on 
                                                        ADSP-21535 Rev.0.2
                1.0         12/17/2000  Manoj&Siva      Original            
                
Description     :   This program implements a T tap FIR filtering for 1.31 format
                    data and coefficients. 
	
Implementation  :   (d.h*c.h) + (d.h*c.l+c.h*d.l) >> 16, where d is data and c 
                    is the coefficient
Prototype       :
                    void  _fir_fr24
                              (
                              fract32 *,    //Pointer to the input
                              fract32 *,    //Pointer to the output
                              fract32 *,    //Pointer to the coefficients
                              fract32 *,    //Pointer to the delay
                              int,          //Number of coefficients
                              int,          //Number of samples
                              fract32 *     //Read write Pointer
                              )
Registers Used  :   A0, A1, R0-R3, I0-I3, B1, B2, M0, L0-L3, P0-P2, LC0, LC1
	
Performance     :
                    Initializations : 23 Cycles
	                Core Cycle Count: N*(2*T + 4)  Cycles, 
	                where N is the number of data samples
	                For N=128, T=8
	                Cycle count= 3125 cycles
********************************************************************************/   

.section L1_code;
.align 8;
.global    __fir_fr24;

__fir_fr24 :
    
    I0=R0; 			        // ADDRESS OF INPUT ARRAY  
	I3=R1;  		        // ADDRESS OF OUTPUT ARRAY
    I2=R2;                  // POINTER TO FILTER COEFFICIENTS
    B2=R2;
    
    P2=[SP+12];             // POINTER TO DELAY LINE BUFFER
	R1=[SP+16];             // NUMBER OF FILTER COEFFICIENTS 
	P0=[SP+20];             // NUMBER OF INPUT SAMPLES
    P1=[SP+24];       	    // ARRDESS OF READ WRITE POINTER
	I1=P2;     			    // INDEX TO READ/WRITE POINTER
	B1=P2;				    // INITIALISE B1 AND L1 

	R3=R1<<2;               // EACH COEFFICIENT IS OF 32 BIT FETCH
	L0=0;
	L3=0;
	L1=R3;      		    // FOR  DELAY LINE CIRCULAR BUFFER
    L2=R3;

   	P2=R1;                  //INNER LOOP COUNT TO NUMBER OF FILTER COEFFICIENTS

 	M0=8;
	R0=[I0++];
	A1=A0=0 || [I1--]=R0||R1=[I2++];
	                        //FETCH INPUT AND FILTER COEFF.


	LSETUP(FIR_START,FIR_END)LC0=P0;
	                        //LOOP SETUP FOR NUMBER OF INPUT SAMPLES
FIR_START:

	    LSETUP(MAC_ST,MAC_END)LC1=P2;
	                        //LOOP SETUP FOR NUMBER OF FILTER COEFFS
MAC_ST:     R2=(A0+=R0.H*R1.H) , A1+=R0.H*R1.L (M);
MAC_END:    R3=(A1+=R1.H*R0.L) (M) || R0=[I1--] || R1=[I2++];
		    R3=R3>>>15 || I1+=M0 ||  R0=[I0++];
		    R3=R2+R3 (S)||[I1--]=R0;
FIR_END:
        A1=A0=0 ||[I3++]=R3;//FETCH INPUT AND FILTER COEFF.
							//Rounded FIR Output in 32 bits		
	L1=0;
	L2=0;

	RTS;