pro read_pkt_file_406, $
	pfile=pfile, pkt_info=pkt_info, $
	pkt_struct=pkt_struct, pkt_data=pkt_data, $
	verbose=verbose, no_pctr=no_pctr, $
	frac=frac,daytime=daytime

expected_apid = pkt_info.expected_apid
apid_name = pkt_info.apid_name
pkt_size = pkt_info.pkt_size	; bytes.
hdr_size = pkt_info.hdr_size	; bytes.

data_size = pkt_size - hdr_size ; bytes.

openu, lun, pfile, /get_lun

; get size of file, and determine number of packet contained within.
fs = fstat( lun)
file_size = fs.size
npkts = floor( file_size/pkt_size)

if keyword_set( verbose) then $
	message, /info, string( file_size, npkts, format='("file size:",I9,",",X,"npkts:",I9,".")')

; here we use POINT_LUN and the PKT_SIZE variable to move to the N-th packet in the file,
; and read M packets, starting with that N-th packet.
; NOT YET IMPLEMENTED.

pkt_buff = assoc( lun, bytarr( pkt_size))

ul64_256 = ulong64( 256)

; elapsed seconds between 1 Jan 1900 and 1 Jan 1970;
; does not include UTC leap seconds.
dt_epoch = ulong64( 3600L*24L)*ulong64(julday( 1, 1, 1970, 0, 0, 0) - julday( 1, 1, 1900, 0, 0, 0))	; s.

; elapsed seconds between first sample of packet and assigned header time stamp.
dt_packet = 0.d

pkt_struct = { clock:ulon64arr( npkts), $
	subsec:ulonarr( npkts), $
	t_hdr:dblarr( npkts), $
	selection:bytarr( npkts), $
	speed:bytarr( npkts), $
	samp_rate:uintarr( npkts), $
	n_sel_chan:intarr( npkts), $
	apid:ulonarr( npkts), $
	pseq_ctrl:bytarr( npkts), $
	apid_ctr:bytarr( npkts), $
	pkt_num:ulonarr( npkts) $
}

pkt_data = { $
	iefi_bias:uintarr( npkts, 6), $
	iefi_usher:bytarr( npkts, 6), $
	iefi_guard:bytarr( npkts, 6), $
	iefi_braid:bytarr( npkts), $
	iefi_temp:bytarr( npkts, 3), $
	iesa_imcp:bytarr( npkts), iesa_emcp:bytarr( npkts), $
	iesa_iswp:bytarr( npkts), iesa_eswp:bytarr( npkts), $
	iesa_egain:bytarr( npkts),iesa_igain:bytarr( npkts), $
	iesa_enables:bytarr( npkts), $
	iesa_pulser:bytarr( npkts), $
	iesa_eswpv:bytarr( npkts), iesa_ehvi:bytarr( npkts), $
	iesa_emcpi:bytarr( npkts), iesa_emcpv:bytarr( npkts), $
	iesa_iswpv:bytarr( npkts), iesa_ihvi:bytarr( npkts), $
	iesa_imcpi:bytarr( npkts), iesa_imcpv:bytarr( npkts), $
	ietc_config:bytarr( npkts), ietc_table:bytarr( npkts), $
	ietc_scpot:intarr( npkts), $
	ietc_covers:bytarr( npkts), $
	isst1_temp:bytarr( npkts), isst2_temp:bytarr( npkts), $
	isst_bias:bytarr( npkts), $
	isst_25vref:bytarr( npkts), $
	isst_d1:bytarr( npkts), $
	isst_d2:bytarr( npkts), $
	isst_d3:bytarr( npkts), $
	isst_d4:bytarr( npkts), $
	ifgm_config:bytarr( npkts), $
	ifgm_message:bytarr( npkts), $
	ifgm_control:uintarr( npkts), ifgm_phase:uintarr( npkts), $
	ifgm_sampling:bytarr( npkts), $
	ifgm_xy:bytarr( npkts), ifgm_zr:bytarr( npkts), $
	iefi_config:bytarr( npkts), $
	ifbanksel:bytarr( npkts), ifilter1:bytarr( npkts), ifilter2:bytarr( npkts), $
	ideppair:bytarr( npkts), idepstat:bytarr( npkts), iboombits:bytarr( npkts), $
	idlena:bytarr( npkts), idlenb:bytarr( npkts), ideplimit:bytarr( npkts), $
	ifitmode:bytarr( npkts), $
	icmp_spare:bytarr( npkts, 8), $
	isci_status:bytarr( npkts, 8), $
	ispare:bytarr( npkts, 12), $
	bau_status:bytarr( npkts), $
	ilvps_sctemp:bytarr( npkts), $
	idpu_sctemp:bytarr( npkts), $
	ispb_sctemp:bytarr( npkts), $
	isst_sctemp:bytarr( npkts), $
	idpu_28i:bytarr( npkts), $
	iact_28i:bytarr( npkts), $
	prmy_htri:bytarr( npkts), $
	sncd_htri:bytarr( npkts) $
}

p = 0L
b0 = bytarr( pkt_size)

; this algorithm for random access to the last frac's worth of the packets
; in the file won't work with variable-length packets,
; so turn it off for now.
if keyword_set( frac) then begin
	message, /info, 'FRAC keyword ignored because of variable-length packets.'
;	i0 = floor( (1.0-frac)*(npkts - 1L)) > 0L
;	i1 = npkts -1L
endif else begin
	i0 = 0L
	i1 = npkts-1L
endelse

if keyword_set( verbose) then $
	message, /info, string( npkts, i0, i1, format='("npkts, i0, i1:",I5.5,",",X,I5.5,",",X,I5.5)')

point_lun, lun, i0*pkt_size

for i=i0,i1 do begin

;	b0 = pkt_buff[ i]
	readu, lun, b0
	pkt_struct.clock[ i] = ulong64( b0[ 9] + $
		ul64_256*( b0[ 8] + $
		ul64_256*( b0[ 7] + $
		ul64_256*( b0[ 6]))))

	pkt_struct.subsec[ i] = ulong( b0[ 11] + 256UL*b0[ 10])


	pkt_struct.apid[ i] = b0[ 1] + 256UL*(b0[ 0] mod 8)

	pkt_struct.pseq_ctrl[ i] = b0[ 2]
	pkt_struct.apid_ctr[ i] = b0[ 3]

; translate pseq_ctrl and apid_ctr bytes to APID number.
	pkt_struct.pkt_num[ i] = pkt_struct.apid_ctr[ i] + 256UL*( pkt_struct.pseq_ctrl[ i] mod 64)

	if keyword_set( verbose) or ( not keyword_set( no_pctr) and (i mod 100 eq 1)) then $
		message, /info, string( i, npkts, pkt_struct.apid[ i], pkt_struct.pseq_ctrl[ i], pkt_struct.apid_ctr[ i], pkt_struct.pkt_num[ i], $
			pkt_struct.clock[ i], pkt_struct.subsec[ i], $
			format='("pnum:",I5.5,X,"of",X,I5.5,X,"APID:",Z4.4,X,"pseq_ctrl:",Z2.2,X,"apid_ctr:",Z2.2,X,"pkt_num:",Z4.4,X,"clock, subsec:",I15.15,X,I7.7)')

	if pkt_struct.apid[ i] ne expected_apid then begin
		message, /info, $
			string( pkt_struct.apid[i], expected_apid, format='("apid (current, expected):","(",Z4.4,X,Z4.4,")")')
			stop
	endif


	t_hdr = double( pkt_struct.clock[i] - dt_epoch) + double( pkt_struct.subsec[i])/(65536.0)	; s.
        if keyword_set(daytime) then dt=0. else dt=3600.   ;Daylight Saving Time
	pkt_struct.t_hdr[ i] = t_hdr - 7*3600. - dt  ;West Time Zone

; unpack data into the arrays in the pkt_data structure.
	for j=0L,5L do begin $
		pkt_data.iefi_bias[ i, j] = b0[ 12+2*j] + 256UL*b0[ 13+2*j]
		pkt_data.iefi_usher[ i, j] = b0[ 24+j]
		pkt_data.iefi_guard[ i, j] = b0[ 30+j]
		endfor

	pkt_data.iefi_braid[ i] = b0[ 36]
	for j=0L,2L do $
		pkt_data.iefi_temp[ i, j] = b0[ 37 + j]

	pkt_data.iesa_imcp[ i] = b0[ 40]
	pkt_data.iesa_emcp[ i] = b0[ 41]
	pkt_data.iesa_iswp[ i] = b0[ 42]
	pkt_data.iesa_eswp[ i] = b0[ 43]
	pkt_data.iesa_egain[ i] = b0[ 44]
	pkt_data.iesa_igain[ i] = b0[ 45]
	pkt_data.iesa_enables[ i] = b0[ 46]
	pkt_data.iesa_pulser[ i] = b0[ 47]
	pkt_data.iesa_eswpv[ i] = b0[ 48]
	pkt_data.iesa_ehvi[ i] = b0[ 49]
	pkt_data.iesa_emcpi[ i] = b0[ 50]
	pkt_data.iesa_emcpv[ i] = b0[ 51]
	pkt_data.iesa_iswpv[ i] = b0[ 52]
	pkt_data.iesa_ihvi[ i] = b0[ 53]
	pkt_data.iesa_imcpi[ i] = b0[ 54]
	pkt_data.iesa_imcpv[ i] = b0[ 55]

	pkt_data.ietc_config[ i] = b0[ 56]
	pkt_data.ietc_table[ i] = b0[ 57]
	pkt_data.ietc_scpot[ i] = b0[ 58] + 256*b0[ 59]	; NOTE:  SIGNED, rather than UNSIGNED!
	pkt_data.ietc_covers[ i] = b0[ 60]

	pkt_data.isst1_temp[ i] = b0[ 61]
	pkt_data.isst2_temp[ i] = b0[ 62]
	pkt_data.isst_bias[ i] = b0[ 63]
	pkt_data.isst_25vref[ i] = b0[ 64]
	pkt_data.isst_d1[ i] = b0[ 65]
	pkt_data.isst_d2[ i] = b0[ 66]
	pkt_data.isst_d3[ i] = b0[ 67]
	pkt_data.isst_d4[ i] = b0[ 68]

	pkt_data.ifgm_config[ i] = b0[ 71]
	pkt_data.ifgm_message[ i] = b0[ 72]
	pkt_data.ifgm_control[ i] = b0[ 73] + 256UL*b0[ 74]
	pkt_data.ifgm_phase[ i] = b0[ 75] + 256UL*b0[ 76]
	pkt_data.ifgm_sampling[ i] = b0[ 77]
	pkt_data.ifgm_xy[ i] = b0[ 78]
	pkt_data.ifgm_zr[ i] = b0[ 79]

	pkt_data.iefi_config[ i] = b0[ 80]

	pkt_data.ifbanksel[ i] = b0[ 81]
	pkt_data.ifilter1[ i] = b0[ 82]
	pkt_data.ifilter2[ i] = b0[ 83]

	pkt_data.ideppair[ i] = b0[ 84]
	pkt_data.idepstat[ i] = b0[ 85]
	pkt_data.iboombits[ i] = b0[ 86]
	pkt_data.idlena[ i] = b0[ 87]
	pkt_data.idlenb[ i] = b0[ 88]
	pkt_data.ideplimit[ i] = b0[ 89]

	pkt_data.ifitmode[ i] = b0[ 90]

	for j=0L,7L do $
		pkt_data.icmp_spare[ i, j] = b0[ 91 + j]

	for j=0L,7L do $
		pkt_data.isci_status[ i, j] = b0[ 99 + j]

	for j=0L,11L do $
		pkt_data.ispare[ i, j] = b0[ 107 + j]

	pkt_data.bau_status[ i] = b0[ 119]
	pkt_data.ilvps_sctemp[ i] = b0[ 120]
	pkt_data.idpu_sctemp[ i] = b0[ 121]
	pkt_data.ispb_sctemp[ i] = b0[ 122]
	pkt_data.isst_sctemp[ i] = b0[ 123]
	pkt_data.idpu_28i[ i] = b0[ 124]
	pkt_data.iact_28i[ i] = b0[ 125]
	pkt_data.prmy_htri[ i] = b0[ 126]
	pkt_data.sncd_htri[ i] = b0[ 127]


endfor	; for i=... loop over packets in file.

free_lun, lun

return
end