mirror of https://github.com/saitohirga/WSJT-X.git
225 lines
6.5 KiB
Fortran
225 lines
6.5 KiB
Fortran
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subroutine mskrtd(id2,nutc0,tsec,ntol,line)
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! Real-time decoder for MSK144.
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! Analysis block size = NZ = 7168 samples, t_block = 0.597333 s
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! Called from hspec() at half-block increments, about 0.3 s
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parameter (NZ=7168) !Block size
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parameter (NSPM=864) !Number of samples per message frame
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parameter (NFFT1=8192) !FFT size for making analytic signal
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parameter (NAVGMAX=7) !Coherently average up to 7 frames
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parameter (NPTSMAX=7*NSPM) !Max points analyzed at once
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integer*2 id2(NZ) !Raw 16-bit data
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character*22 msgreceived !Decoded message
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character*80 line !Formatted line with UTC dB T Freq Msg
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complex cdat(NFFT1) !Analytic signal
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complex cdat2(NFFT1) !Signal shifted to baseband
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complex c(NSPM) !Coherently averaged complex data
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complex ct(NSPM)
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complex ct2(2*NSPM)
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complex cs(NSPM)
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complex cb(42) !Complex waveform for sync word
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complex cfac,cca,ccb
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complex cc(0:NSPM-1)
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! integer*8 count0,count1,count2,count3,clkfreq
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integer s8(8),hardbits(144)
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integer iloc(1)
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integer ipeaks(10)
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integer nav(6)
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integer*1 decoded(80)
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real cbi(42),cbq(42)
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real d(NFFT1)
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real xcc(0:NSPM-1)
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real xccs(0:NSPM-1)
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real pp(12) !Half-sine pulse shape
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real softbits(144)
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real lratio(128)
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real llr(128)
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logical first
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data first/.true./
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data s8/0,1,1,1,0,0,1,0/
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data nav/1,2,3,5,7,9/
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save first,cb,fs,pi,twopi,dt,s8,pp,t03,t12,nutc00
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! call system_clock(count0,clkfreq)
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if(first) then
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pi=4.0*atan(1.0)
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twopi=8.0*atan(1.0)
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fs=12000.0
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dt=1.0/fs
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do i=1,12 !Define half-sine pulse
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angle=(i-1)*pi/12.0
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pp(i)=sin(angle)
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enddo
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! Define the sync word waveforms
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s8=2*s8-1
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cbq(1:6)=pp(7:12)*s8(1)
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cbq(7:18)=pp*s8(3)
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cbq(19:30)=pp*s8(5)
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cbq(31:42)=pp*s8(7)
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cbi(1:12)=pp*s8(2)
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cbi(13:24)=pp*s8(4)
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cbi(25:36)=pp*s8(6)
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cbi(37:42)=pp(1:6)*s8(8)
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cb=cmplx(cbi,cbq)
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first=.false.
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t03=0.0
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t12=0.0
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nutc00=-1
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endif
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msgreceived=' '
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max_iterations=10
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niterations=0
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d(1:NZ)=id2
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rms=sqrt(sum(d(1:NZ)*d(1:NZ))/NZ)
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if(rms.lt.1.0) return
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fac=1.0/rms
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d(1:NZ)=fac*d(1:NZ)
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d(NZ+1:NFFT1)=0.
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call analytic(d,NZ,NFFT1,cdat) !Convert to analytic signal and filter
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nmessages=0
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line=char(0)
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nshort=0
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npts=7168
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nsnr=-4 !### Temporary ###
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do iavg=1,5
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navg=nav(iavg)
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ndf=nint(7.0/navg) + 1
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xmax=0.0
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bestf=0.0
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! call system_clock(count1,clkfreq)
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do ifr=-ntol,ntol,ndf !Find freq that maximizes sync
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ferr=ifr
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call tweak1(cdat,NPTS,-(1500+ferr),cdat2)
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c=0
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do i=1,navg
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ib=(i-1)*NSPM+1
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ie=ib+NSPM-1
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c(1:NSPM)=c(1:NSPM)+cdat2(ib:ie)
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enddo
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cc=0
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ct2(1:NSPM)=c
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ct2(NSPM+1:2*NSPM)=c
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do ish=0,NSPM-1
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cc(ish)=dot_product(ct2(1+ish:42+ish)+ct2(336+ish:377+ish),cb(1:42))
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enddo
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xcc=abs(cc)
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xb=maxval(xcc)/(48.0*sqrt(float(navg)))
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if(xb.gt.xmax) then
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xmax=xb
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bestf=ferr
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cs=c
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xccs=xcc
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endif
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enddo
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! call system_clock(count2,clkfreq)
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fest=1500+bestf
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c=cs
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xcc=xccs
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! Find 2 largest peaks
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do ipk=1,2
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iloc=maxloc(xcc)
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ic2=iloc(1)
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ipeaks(ipk)=ic2
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xcc(max(0,ic2-7):min(NSPM-1,ic2+7))=0.0
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enddo
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do ipk=1,2
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do is=1,3
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ic0=ipeaks(ipk)
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if(is.eq.2) ic0=max(1,ic0-1)
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if(is.eq.3) ic0=min(NSPM,ic0+1)
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ct=cshift(c,ic0-1)
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! Estimate final frequency error and carrier phase.
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cca=sum(ct(1:1+41)*conjg(cb))
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ccb=sum(ct(1+56*6:1+56*6+41)*conjg(cb))
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cfac=ccb*conjg(cca)
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! ffin=atan2(imag(cfac),real(cfac))/(twopi*56*6*dt)
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phase0=atan2(imag(cca+ccb),real(cca+ccb))
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! Remove phase error: rotate constellation so sample points lie on I/Q axes
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cfac=cmplx(cos(phase0),sin(phase0))
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ct=ct*conjg(cfac)
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! Use matched filter
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softbits(1)=sum(imag(ct(1:6))*pp(7:12)) + &
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sum(imag(ct(864-5:864))*pp(1:6))
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softbits(2)=sum(real(ct(1:12))*pp)
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do i=2,72
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softbits(2*i-1)=sum(imag(ct(1+(i-1)*12-6:1+(i-1)*12+5))*pp)
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softbits(2*i)=sum(real(ct(7+(i-1)*12-6:7+(i-1)*12+5))*pp)
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enddo
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! Number of hard errors in sync word is a good discriminator for
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! frames that have reasonable probability of decoding
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hardbits=0
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do i=1,144
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if(softbits(i) .ge. 0.0) then
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hardbits(i)=1
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endif
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enddo
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nbadsync1=(8-sum((2*hardbits(1:8)-1)*s8))/2
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nbadsync2=(8-sum((2*hardbits(1+56:8+56)-1)*s8))/2
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nbadsync=nbadsync1+nbadsync2
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if(nbadsync .gt. 3) cycle
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! Normalize softsymbols before submitting to decoder
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sav=sum(softbits)/144
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s2av=sum(softbits*softbits)/144
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ssig=sqrt(s2av-sav*sav)
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softbits=softbits/ssig
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sigma=0.70
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lratio(1:48)=softbits(9:9+47)
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lratio(49:128)=softbits(65:65+80-1)
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llr=2.0*lratio/(sigma*sigma)
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call bpdecode144(llr,max_iterations,decoded,niterations)
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if(niterations .ge. 0.0) then
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call extractmessage144(decoded,msgreceived,nhashflag)
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if(nhashflag .gt. 0) then ! CRCs match, so print it
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write(line,1020) nutc0,nsnr,tsec,nint(fest),msgreceived,char(0)
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1020 format(i6.6,i4,f5.1,i5,' ^ ',a22,a1)
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endif
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goto 999
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else
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msgreceived=' '
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ndither=-99 !Bad hash flag = -99
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endif
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enddo !Slicer dither
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enddo !Peak loop
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enddo
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msgreceived=' '
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ndither=-98
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999 continue
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! call system_clock(count3,clkfreq)
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! t12=t12 + float(count2-count1)/clkfreq
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! t03=t03 + float(count3-count0)/clkfreq
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! if(navg.gt.7) navg=0
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! write(*,3002) nutc0,tsec,t12,t03,xmax,nint(bestf),navg, &
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! nbadsync,niterations,ipk,is,msgreceived(1:19)
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! write(62,3002) nutc0,tsec,t12,t03,xmax,nint(bestf),navg, &
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! nbadsync,niterations,ipk,is,msgreceived(1:19)
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!3002 format(i6,f6.2,2f7.2,f6.2,i5,5i3,1x,a19)
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return
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end subroutine mskrtd
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