subroutine recvpkt(iarg)

! Receive timf2 packets from Linrad and stuff data into array id().
! (This routine runs in a background thread and will never return.)

  parameter (NSZ=2*60*96000)
  real*8 d8(NSZ)
  integer*1 userx_no,iusb
  integer*2 nblock,nblock0
  logical synced
  real*8 center_freq,buf8
  common/plrscom/center_freq,msec,fqso,iptr,nblock,userx_no,iusb,buf8(174)
  include 'datcom.f90'
  include 'gcom1.f90'
  include 'gcom2.f90'
  equivalence (id,d8)
  data nblock0/0/,kb/1/,npkt/0/,nw/0/,ns0/99/
  data sqave/0.0/,u/0.001/,rxnoise/0.0/,kbuf/1/,lost_tot/0/
  data multicast0/-99/
  save

1 call setup_rsocket(multicast)     !Open socket for multicast/unicast data
  k=0
  kk=0
  kxp=0
  kb=1
  nsec0=-999
  fcenter=144.125                   !Default (startup) frequency)
  multicast0=multicast
  ntx=0
  synced=.false.

10 if(multicast.ne.multicast0) go to 1
  call recv_pkt(center_freq)

! Should receive a new packet every 174/96000 = 0.0018125 s
  npkt=npkt+1
  nsec=mod(Tsec,86400.d0)           !Time according to MAP65
  nseclr=msec/1000                  !Time according to Linrad
  fcenter=center_freq

! Reset buffer pointers at start of minute.
  ns=mod(nsec,60)
  if(ns.lt.ns0) then
     if(ntx.eq.0) kb=3-kb
     k=(kb-1)*60*96000
     ndone1=0
     ntx=0
     lost_tot=0
     kxp=k
     npkt=0
     synced=.true.
  endif
  ns0=ns

  if(transmitting.eq.1) ntx=1

! Check for lost packets
  lost=nblock-nblock0-1
  if(lost.ne.0) then
     nb=nblock
     if(nb.lt.0) nb=nb+65536
     nb0=nblock0
     if(nb0.lt.0) nb0=nb0+65536
     lost_tot=lost_tot + lost               ! Insert zeros for the lost data.
     do i=1,174*lost
        k=k+1
        d8(k)=0
     enddo
  endif
  nblock0=nblock

  tdiff=mod(0.001d0*msec,60.d0)-mod(Tsec,60.d0)
  if(tdiff.lt.-30.) tdiff=tdiff+60.
  if(tdiff.gt.30.) tdiff=tdiff-60.

! Test for buffer full
  if((kb.eq.1 .and. (k+174).gt.NSMAX) .or.                          &
       (kb.eq.2 .and. (k+174).gt.2*NSMAX)) go to 20

! Move data into Rx buffer and compute average signal level.
  sq=0.
  do i=1,174
     k=k+1
     d8(k)=buf8(i)
     k2=k
     n=1
     if(k.gt.NSMAX) then
        k2=k2-NSMAX
        n=2
     endif
     x1=id(1,k2,n)
     x2=id(2,k2,n)
     x3=id(3,k2,n)
     x4=id(4,k2,n)
     sq=sq + x1*x1 + x2*x2 + x3*x3 + x4*x4
  enddo
  sqave=sqave + u*(sq-sqave)
  rxnoise=10.0*log10(sqave) - 48.0
  kxp=k

20 if(nsec.ne.nsec0) then
     nsec0=nsec
     mutch=nseclr/3600
     mutcm=mod(nseclr/60,60)
     mutc=100*mutch + mutcm

! If we have not transmitted in this minute, see if it's time to start FFTs
     if(ntx.eq.0) then
        if(ns.ge.nt1 .and. ndone1.eq.0 .and. synced) then
           nutc=mutc
           fcenter=center_freq
           kbuf=kb
           kk=k
           ndiskdat=0
           ndone1=1
        endif

! See if it's time to start second stage of processing
        if(ndone1.eq.1 .and. ns.ge.nt2) then
           kk=k
           nlost=lost_tot                         ! Save stats for printout
        endif
     endif

     tt=npkt*174.0/96000.0
!     if(ns.le.5 .or. ns.ge.46) write(*,3001) ns,ndone1,kb,  &
!          kbuf,ntx,kk,tdiff,tt
!3001 format(5i4,i11,2f8.2)

  endif
  go to 10

end subroutine recvpkt