function [DF_HEAD,SID_SPEC,totrecs,datacat,pos,SID_REC]=DSGread(FileName,numrecs, startpos)
%% Program to load DSG files and extract information.  File always closed at end of call.
% [DF_HEAD,SID_SPEC,totrecs,datacat,pos,SID_REC]=DSGread(FileName,numrecs,startpos)

% DF_HEAD
% SID_SPEC
% totrecs = total records in file
% pos = position in bytes at end of function
% datacat = concatenated data (extracted from SID_RECs)
% SID_REC = data in SID_REC structure

% FileName = DSG filename (note very old .vdf files also loaded)
% numrecs = number of SID_RECS to read. =0 to read entire file
% startpos = start position (in bytes) to start reading numrecs

% To read in parts of file use output argument pos to keep track of
% location in file.

%%
fid=fopen(FileName);
if(fid<1)
    disp('Unable to Open File');
    FileName
    return
end 

[path,file,filetype]=fileparts(FileName);

% Read in DF_Head
DF_HEAD.Version = fread(fid,1,'uint32');
DF_HEAD.UserID = fread(fid,1,'uint32');
DF_HEAD.sec = fread(fid,1,'uint8');
DF_HEAD.min = fread(fid,1,'uint8');
DF_HEAD.hour = fread(fid,1,'uint8');
DF_HEAD.day = fread(fid,1,'uint8');
DF_HEAD.mday = fread(fid,1,'uint8');
DF_HEAD.month = fread(fid,1,'uint8');
DF_HEAD.year = fread(fid,1,'uint8'); 
DF_HEAD.timezone = fread(fid,1,'int8');

if strcmpi(filetype,'.VDF') == 1
    DF_HEAD.NU = fread(fid,16,'uint32'); 
end

if(DF_HEAD.Version>=1010) 
    DF_HEAD.Lat=fread(fid,1,'float32');
    DF_HEAD.Lon=fread(fid,1,'float32');
    DF_HEAD.depth=fread(fid,1,'float32');
    DF_HEAD.DSGcal=fread(fid,1,'float32');
    DF_HEAD.hydroCal=fread(fid,1,'float32');
    DF_HEAD.lpFilt=fread(fid,1,'float32');
end
    
pos(2) = ftell(fid);
  
% Read in SID_SPECS until get all zeroes
notdone=1;
SID_SPEC=[];
nSIDSPEC=1;
while(notdone)
    SID_SPEC(nSIDSPEC).SID = fread(fid,4,'uint8=>char');
    SID_SPEC(nSIDSPEC).nBytes = fread(fid,1,'uint32');
    SID_SPEC(nSIDSPEC).NumChan = fread(fid,1,'uint32');
    SID_SPEC(nSIDSPEC).StoreType = fread(fid,1,'uint32');
    SID_SPEC(nSIDSPEC).CircType = fread(fid,1,'uint32');
    SID_SPEC(nSIDSPEC).DForm = fread(fid,1,'uint32');
    SID_SPEC(nSIDSPEC).SP256 = fread(fid,1,'uint32'); % Sample period (us) x 256
    
    if strcmp(SID_SPEC(1).SID','VIPR') ==1
        SID_SPEC(nSIDSPEC).RECPTS=0;
        SID_SPEC(nSIDSPEC).RECINT=0;
    else
        SID_SPEC(nSIDSPEC).RECPTS=fread(fid,1,'uint32');
        SID_SPEC(nSIDSPEC).RECINT=fread(fid,1,'uint32');
    end
    
    if(SID_SPEC(nSIDSPEC).nBytes==0)
        notdone=0;
    end
    nSIDSPEC=nSIDSPEC+1; 
end
nSIDSPEC=nSIDSPEC-1;
SID_SPEC(nSIDSPEC)=[];  % delete last one with all zeroes
nSIDSPEC=nSIDSPEC-1;

pos(3) = ftell(fid);

SID_REC=[];
datacat=[];

fseek(fid, 0, 'eof');  
npts=ftell(fid)/2;
totrecs=floor((npts-8-(18*length(SID_SPEC)))/(SID_SPEC(1).nBytes/2)); %subtract off size of DF_HEAD and SID_SPEC
       
if(nargout<4) % only reading in DF_HEAD, SID_SPEC, totrecs
    fclose(fid); 
    return;
end

fseek(fid,pos(3),'bof');  % put back at end of SID_SPEC
    
% Read in next SID_REC header, and based on ID, read in correct number of
% points
eofstat=0;
reccounter=0;

if(nargin==3)
    if(startpos(1)>0)
        fseek(fid,startpos(1),'bof');
    end
end

while(eofstat==0)
    reccounter=reccounter+1;
    SID_REC(reccounter).nSID=fread(fid,1,'uint8');
    SID_REC(reccounter).Chan=fread(fid,1,'uint8');
    SID_REC(reccounter).TS256=fread(fid,1,'uint64');  % Timestamp in usecs * 256 since block record started
    cur_sid=(SID_REC(reccounter).nSID)+1;
    if(cur_sid == 1)         
        nsamples=(SID_SPEC(cur_sid).nBytes)/2;  %/2 because in bytes
       
        SID_REC(reccounter).data=fread(fid,nsamples,'int16');
        datacat = vertcat(datacat,SID_REC(reccounter).data);
       
    else      
        SID_REC(reccounter)=[]; %last one was bad so delete this entry
        reccounter=reccounter-1;        
    end
    
    eofstat = feof(fid);
    
    if(numrecs>0 && (reccounter>=numrecs))
        break;
    end
end
    pos(1) = ftell(fid);  % get position of file
    fclose(fid);

%% -------------------------------------------------------------------------

% DSG file structure
% DF_HEAD
% several SID_SPECS followed by SID_SPEC with all zeros
% SID_REC

% DF_HEAD <ver 1010
% typedef struct 
% {
% 	ULONG Version;  
%   	ULONG UserID;
%   	TIME_HEAD RecStartTime;
% }DF_HEAD;
% 

% DF_HEAD VERSION 1010 and later
% typedef struct 
% {
% 	ULONG Version;  
%   ULONG UserID;
%   TIME_HEAD RecStartTime;
% 	float Lat;
% 	float Lon;
% 	float depth;
% 	float DSGcal;
% 	float hydroCal;
% 	float lpFilt;
% }DF_HEAD;

% typedef struct 
% {
% 	BYTE 	sec;  
% 	BYTE 	min;  
% 	BYTE 	hour;  
% 	BYTE 	day;  
% 	BYTE 	mday;  
% 	BYTE 	month;  
% 	BYTE 	year;  
% 	BYTE	NU;  
% }TIME_HEAD;

% typedef struct 
% {
% 	ULONG	SID;
% 	ULONG 	nBytes;			// Size in bytes of this record (excluding header)
% 	ULONG	NumChan;		// Number of expected channels in store
% 	ULONG	StoreType;		// See TTank stuff
% 	ULONG	CircType;		// Circuit type they might generate this store in OpenEx (1-5)
% 	ULONG	DForm;			// See TTank stuff
% 	ULONG	SP256;			// Sample period (us) x 256
%   ULONG   RECPTS;         //=0 for continuous, other for stutter record
%   ULONG   RECINT;         //interval between buffers
% }SID_SPEC;
% 
% typedef struct 
% {
% 	BYTE	nSID;			// This is record I/D
% 	BYTE	Chan;			// Channel index modifying SID of other user value or lower half of value
% 	DLONG	TS256;			// Timestamp in usecs * 256 since block record started
% }SID_REC;

% [FileName,PathName,FilterIndex] = uigetfile({'*.dsg','DSG files (*.dsg)'},'Select a DSG file');
%     if isequal(FileName,0)|isequal(PathName,0)
%         return
%     end
%     
% cd(PathName);