dc_filter.s43

msp430F437三相电表DEMO(编译器 IAR 3.42A）

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//	File: shift48.s43
//
//  Steve Underwood <[e-mail]>
//  Texas Instruments Hong Kong Ltd.
//
//  $Id$
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//--------------------------------------------------------------------------
#include "io.h"

/* A routine to filter away the DC content from an AC mains waveform
   signal. It does this my using a heavily damped integrator to estimate
   the DC level. The current DC level is then subtracted from the signal. */

/* One would like to estimate DC by something like:
     z += ((((int32_t) x << 15) - z) >> 14);
     return  x - (z >> 15);
   but this:
     z += ((((int32_t) x << 16) - z) >> 14);
     return  x - (z >> 16);
  is a bit faster, and the shift by 16 will never
  cause an overflow in this application. However,
  remember this is not a generic DC filter! */

;int16_t dc_filter(register int32_t *p, register int16_t x)
    public dc_filter

    RSEG CODE
dc_filter
#if defined(__MSP430_HAS_MSP430X_CPU__)
    pushm.w #2,R9
#else
    push.w  R8
    push.w  R9
#endif
    clr     R9
    mov     R14,R8
    sub     0(R12),R9       ; subtract filter_state from (sample << 16)
    subc    2(R12),R8
    rla     R9              ; >> 14
    rlc     R8
    jc      dc_filter_1
    rlc     R9
    rlc     R8
    rlc     R9
    and     #0x0003,R9
    jmp     dc_filter_2
dc_filter_1
    rlc     R9
    rlc     R8
    rlc     R9
    bis     #0xFFFC,R9
dc_filter_2
    add     0(R12),R8       ; + filter_state
    addc    2(R12),R9
    mov     R8,0(R12)       ; save new filter_state
    mov     R9,2(R12)
    sub     R9,R14          ; sample - filter_state
    mov     R14,R12
#if defined(__MSP430_HAS_MSP430X_CPU__)
    popm.w  #2,R9
    reta
#else
    pop.w   R9
    pop.w   R8
    ret
#endif
    end