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Discussion Groups | TMS320C3x | Simple Sine Wave on the C31

Technical discussions about the TI C3x DSPs (including the C31, C32 and C33 DSPs).

  

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Simple Sine Wave on the C31 - Phil - Dec 3 19:23:00 2002

Hi guys,

I need to generate a sine wave on the C31.
This is how I am approaching it, I am writing a C program to generate the
sine wave using phasor multiplication. This program returns a range of floating
point values which correspond to a sine wave. How do I carry on from here
to implement this wave on the C31 or have I gone completely off track already.

I was thinking that maybe its possible to create .asm file from the output
of the C program so that it can be run on the C31. I'm sorry if this seems
rather vague but I have only really just started it.

Any help would be greatly appreciated
rgds
Phil







Re: Simple Sine Wave on the C31 - Keith E. Larson - Dec 3 23:24:00 2002

Hi Phil

You should find the following functions in SIGGEN.C and SIGGEN2.ASM (in the
C_APPS subdirectory) helpful.

Hope this helps,
Keith Larson

#include <math.h>
#include "siggen.h"
//========================================================
// InitSiggen() initializes the signal structure based on
// the desired frequency and sample rate.
//========================================================
void InitSiggen(SIGGEN *S, float Fgen, float Ts)
{ float angle;
angle = 2*pi*Fgen*Ts;
S->TR = cos(angle);
S->TI = sin(angle);
S->DI = 0.0;
S->DR = 1.0;
}
//========================================================
// siggen() generates REAL (cos) and IMAG (sin) complex
// signals using complex multiplication to perform phasor
// rotation. Error feedback is enabled
//========================================================
void siggen(SIGGEN *S)
{ float f;
// complex multiply
f = (S->DR * S->TR) - (S->DI * S->TI);
S->DI = (S->DR * S->TI) + (S->DI * S->TR);
S->DR = f;
// Now fix any (small) amplitude errors
f = 1.5 - 0.5*((S->DI*S->DI) + (S->DR*S->DR));
S->DI *= f;
S->DR *= f;
}
//========================================================
void siggen2(SIGGEN *S); // prototype for ASM version

;-----------------------------------------------------
; SIGGEN2.ASM
; Keith Larson
; TMS320 Applications
; (c) Texas Instruments Inc, 1999
;
; Prototype: void siggen2(&SIGGEN);
;
; Computes a rotating phasor whose value and
; rotational frequency is defined in a SIGGEN
; structure.
;
; typedef struct SIGGEN
; {
; float DR; // R/I phasor (signal)
; float DI;
; float TR; // R/I phase rate (twiddle)
; float TI;
; }
;
; This function uses only registers R0,R1,R2
; and R3 which do not require context save
;
; On entry the stack holds the return address
; and address of the SIGGEN structure
;
; Execution: 16 Cycles:
; Using internal SRAM when data and program
; are not in the same same block
;
; Size: 19 program, 0 data (structure is external)
;-----------------------------------------------------
.globl _siggen2
_siggen2: ;
LDI SP,AR2 ; Load local frame pointer
LDI *-AR2(1),AR2 ; Addr of SIGGEN structure
;====Compute phase rotation ===
ldf *+AR2(1) ,R0 ; DI
|| ldf *AR2++(1),R1 ; DR
MPYF3 *++AR2(1),R1,R2 ; TR*DR
MPYF3 *+AR2(1) ,R0,R3 ; TI*DI
MPYF *+AR2(1) ,R1 ; TI*DR
MPYF *AR2--(2),R0 ; TR*DI
SUBF R3,R2,R2 ; R2=TR*DR-TI*DI
ADDF R0,R1,R1 ; R1=TI*DR+TR*DI
;= FEEDBACK: compute mag^2 ===
MPYF R1,R1,R3 ; R3=I^2
MPYF R2,R2,R0 ; R0=R^2
ADDF R3,R0,R0 ; R0=R^2+I^2
;= FEEDBACK: 1/sqrt(x) apprx ==
MPYF 0.5,R0 ;
SUBRF 1.5,R0 ; R0=1.5-0.5*(R^2+I^2)
;=úst return using free reg==
pop R3 ;
BD R3 ;
;==Scale results and save======
MPYF R0,R1 ;
MPYF R0,R2 ;
STF R2,*+AR2(0) ; Update REAL
|| STF R1,*+AR2(1) ; Update IMAG At 07:23 PM 12/3/02 +0000, you wrote:
>Hi guys,
>
>I need to generate a sine wave on the C31.
>This is how I am approaching it, I am writing a C program to generate the
>sine wave using phasor multiplication. This program returns a range of floating
>point values which correspond to a sine wave. How do I carry on from here
>to implement this wave on the C31 or have I gone completely off track already.
>
>I was thinking that maybe its possible to create .asm file from the output
>of the C program so that it can be run on the C31. I'm sorry if this seems
>rather vague but I have only really just started it.
>
>Any help would be greatly appreciated
>rgds
>Phil
>
+-----------------------------------------------+
|Keith Larson |
|Member Group Technical Staff |
|Texas Instruments Incorporated |
| |
| 281-274-3288 |
| |
| www.micro.ti.com/~klarson |
|-----------------------------------------------+
| TMS320C3x/C4x/VC33 Applications |
| |
| TMS320VC33 |
| The lowest cost and lowest power 500 µw/Mflop |
| floating point DSP on the planet! |
+-----------------------------------------------+