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DSP: Digital Signal Processors

DSP: Digital Signal Processors. Definition. RT development 4 steps. Matlab/C Simulation. RT like Matlab/C Simulation. Real Time. RT like DSP Simulation. RT application. Clock levels. At Home. Definition. Definition. RT development 4 steps.

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DSP: Digital Signal Processors

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  1. DSP: Digital Signal Processors Definition RT development 4 steps Matlab/C Simulation RT like Matlab/C Simulation Real Time RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  2. Definition Definition RT development 4 steps The term “real time” is used to describe a number of different computer features. However, the following definition warrants adoption for this course: Real time is a realization method, in which every specific task is tied to a specific time within the system clock cycle. Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  3. Real-time vs. Off-line Definition RT development 4 steps • Q: What is the difference between a Real-time (RT) algorithm and an Off-line algorithm? • A: The basic idea of a RT algorithm is that only past and present input is available. Namely, we do not have access to future input values. Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  4. RT development 4 steps Definition RT development 4 steps • Matlab/C simulation • RT like Matlab/C simulation • RT like DSP simulation • RT application Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  5. 1. Matlab/C simulation Definition Example: mean calculation RT development 4 steps clear all; N=1000; x=rand(1,N); %---------------------------------------------------------- % Version 1 %---------------------------------------------------------- m1=mean(x); Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels Complex Matlab instructions At Home Alon Slapak, Afeka college

  6. 2. RT like simulation Definition Characteristics: RT development 4 steps • Clock-resembling loop • Access to the “present” value only in the input array. • Updated output in each loop cycle. Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  7. No updated output in each loop cycle. 2.RT like Matlab/C simulation Definition Example: mean calculation RT development 4 steps clear all; N=1000; x=rand(1,N); %---------------------------------------------------------- % Version 2 %---------------------------------------------------------- S=0; for i=1:N, S=S+x(i); end; m2=S/N; Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation This is not RT! – Why? RT application Clock levels At Home Alon Slapak, Afeka college

  8. 1. Clock-resembling loop 2. “present” value only 3. Updated output in each loop cycle 2.RT like Matlab/C simulation Definition Example: mean calculation RT development 4 steps clear all; N=1000; x=rand(1,N); %---------------------------------------------------------- % Version 3 %---------------------------------------------------------- K=50; buf=zeros(1,K); S=0; for i=1:N, S=S-buf(end); buf=[x(i) buf(1:end-1)]; S=S+buf(1); m3(i)=S/K; end; Matlab/C Simulation RT like Matlab/C Simulation RT like simulation characteristics RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  9. 1. Clock-resembling loop 2. “present” value only 3. Updated output in each loop cycle 2.RT like Matlab/C simulation Definition Example: mean calculation – Alpha filter RT development 4 steps clear all; N=1000; x=rand(1,N); %---------------------------------------------------------- % Version 4 %---------------------------------------------------------- S=0; for i=1:N, S=0.99*S+0.01*x(i); m4(i)=S; end; Matlab/C Simulation RT like Matlab/C Simulation RT like simulation characteristics RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  10. Updated output in each loop cycle “present” value only Clock-resembling loop Arrays for input & output samples 3. RT like DSP simulation Definition /////////////////////////////// // void main() /////////////////////////////// void main() { tMaState MaState; MaState.sum = 0; MaState.index = buf; int n; for (n=0; n<N; n++) y[n] = avg_asm(x[n],buf,&MaState); for (n=0; n<N; n++) printf("y[%d] = %d \n",n,y[n]); } RT development 4 steps /************************************* File Name : dsp6_main.c Author : Alon Slapak Date : 13.10.07 **************************************/ #include <stdio.h> #include <stdlib.h> #include <math.h> /////////////////////////////// // Constants /////////////////////////////// #define N 10 #define M 4 /////////////////////////////// // Types /////////////////////////////// typedef struct { int *index; int sum; } tMaState; /////////////////////////////// // Globals /////////////////////////////// int x[N] = {1, 2, 3, -4, -1, -5, 3, 0, 2, -1}; int y[N]; int buf[M] = {0, 0, 0, 0}; /////////////////////////////// // External functions /////////////////////////////// extern int avg_asm(int smp,int *buf, tMaState *t); Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  11. 3. RT like DSP simulationavg_asm function Definition RT development 4 steps /************************************* File Name : DSP6_func.asm Author : Alon Slapak Date : 13.10.07 **************************************/ /////////////////////////////// // Constants /////////////////////////////// #define M 4 .section data1; .section program; .global _avg_asm; _avg_asm: P0 = R2; // State struct pointer L0 = 4*M; // buf length B0 = R1; // buf start address nop; nop; R4 = [P0++]; // buf current index I0 = R4; // Circular buffer nop; nop; R2 = [P0]; // Moving average sum // Moving average R2 = R2 + R0; //sum = sum + new_sample R3 = [I0]; R2 = R2 - R3; //sum = sum - old_sample [I0++] = R0; // Store results [P0--] = R2; // Store the sum R4 = I0; [P0++] = R4; // Store the current index R0 = R2; RTS; _avg_asm.end: Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  12. State structures Definition RT development 4 steps In most RT assembler functions, a state structures maintaining values likebuffers pointers, buffer lengths and updated circular pointers are used: Example 1: Moving Avereage typedef struct { int *index; int sum; } tMaState; Example 2: FIR fract16 typedef struct {    fract16 *h,          /* filter coefficients               */    fract16 *d,          /* start of delay line               */    fract16 *p,          /* read/write pointer                */    int k;                /* number of coefficients            */    int l;                /* interpolation/decimation index*/ } fir_state_fr16; Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  13. 4. RT application Definition RT development 4 steps • Copy the instructions within the clock-resembling loop into the appropriate ISR function. • Copy the initialization instructions into the appropriate initialization function. • Make the required adjustments. Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  14. Core clock (CCLK) • System clock (SCLK) • Application clock (ACLK) • Also: Data clock (DCLK), Input clock (CLKIN) SCLK n+2 n n+1 CCLK App CLK Clock levels Example: CCLK = 400 MHz SCLK = 133 MHz ACLK = 48 kHz Definition RT development 4 steps Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application t[Sec] Clock levels At Home Alon Slapak, Afeka college

  15. n+2 n n+1 t[Sec] Tasks and system clock ticks Definition Example: Moving Average calculation RT development 4 steps Sampling: ADC x S  S +x Matlab/C Simulation S  S – Cyclic_buffer[last] RT like Matlab/C Simulation Cyclic_buffer[first]  x m  S/k RT like DSP Simulation DAC  m RT application Clock levels At Home Spare system clock tick Alon Slapak, Afeka college

  16. Basic mechanisms for RT Definition RT development 4 steps • Interrupts Clock-dependent interrupt is the only option for hard RT applications. • Polling Better fit for RT applications. Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

  17. After the lecture… Definition RT development 4 steps • Run the moving average example • Add the moving buffer length (currently 4) to the state structure, and omit the #define M 4 instruction in the DSP6_func.asm file Matlab/C Simulation RT like Matlab/C Simulation RT like DSP Simulation RT application Clock levels At Home Alon Slapak, Afeka college

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