这个函数看不大懂，求高手解释
function checkData(buffer : array of byte; bufferlength : integer ;var ainfo : CommunicationInfo) : integer;
var
  i : integer;
  startbyytepos : integer;
  FindStartByte : boolean;
  templen : integer;
  index68:integer;
  checksum:byte;
  checkerror:boolean;
  tempint:integer;
begin
  startbyytepos := -1;
  if ainfo.waitforcomplete then //如果是上一桢的后续部分，则合并到上一桢。
  begin
    ainfo.waitforcomplete:=false;
    if ( bufferlength+ainfo.RxBufLengthAll )>300 then
    begin
      bufferlength := 300 - ainfo.RxBufLengthAll;
    end;
    for i:=0 to bufferlength -1 do
    begin
      ainfo.ReceiveBuffer[ ainfo.RxBufLengthAll + i ] := buffer[i];
    end;
    ainfo.RxBufLengthAll := ainfo.RxBufLengthAll + bufferlength;
    //检查是否是一桢已满（如：将一桢分成3片和4片的情况）

    for i:=0 to ainfo.RxBufLengthAll -1 do
      if (ainfo.ReceiveBuffer[i]=$68) and (ainfo.ReceiveBuffer[i+3]=$68) then
      begin
        startbyytepos := i ;
        break;
      end;
    if ( startbyytepos <> -1 ) and ( ainfo.RxBufLengthAll < ainfo.ReceiveBuffer[startbyytepos + 1 ]) then
    begin
      ainfo.waitforcomplete:=true;
    end;
  end
  //如果是新的一桢。
  else
  begin
    for i:=0 to bufferlength-1 do
      if (buffer[i]=$68) and (buffer[i+3]=$68) then
      begin
        startbyytepos:=i;
        break;
      end;
    if startbyytepos <> -1 then   //有68 ** ** 68
    begin
      i:= buffer[startbyytepos+1];
      templen:=buffer[startbyytepos+1];
      if bufferlength < (startbyytepos + 4 + i + 2 ) then //收到的数据<应该有的长度，等待继续接收。
      begin
        ainfo.waitforcomplete:=true;
        for i:=0 to bufferlength - 1 do ainfo.ReceiveBuffer[i]:=buffer[i];
          ainfo.RxBufLengthAll := bufferlength;
      end
      else
      begin
        for i:=0 to templen + 8 do
        begin
          ainfo.ReceiveBuffer[i]:= buffer[startbyytepos + i ];  //多读了几个字节
        end;
        ainfo.RxBufLengthAll := bufferlength;
      end;
    end
    else
    begin
      exit;
    end;
  end;
  if ainfo.waitforcomplete then exit;


  {开始分析命令，先三步校验，若校验错，设置校验失败标志，校验成功后再分析。}
  index68:=-1;
  checkerror := false;
  For i := 0 To ainfo.RxBufLengthAll-1 do
    If (ainfo.ReceiveBuffer[i]=$68) and (ainfo.ReceiveBuffer[i+3]=$68) Then
    begin
      index68 := i;
      break;
    end;
  If index68=-1 then checkerror := true;//无68..68。
  For i := 0 To ainfo.RxBufLengthAll - index68 -1 do
    ainfo.DataBuffer[i]:= ainfo.ReceiveBuffer[index68+i];

  ainfo.DataBufLength:=ainfo.RxBufLengthAll-index68;

  checksum:=0;
  For i:=1 to ainfo.DataBuffer[2] do
    checksum := checksum + ainfo.DataBuffer[i+3];
  If (checksum <> ainfo.DataBuffer[ainfo.DataBuffer[2]+4]) or
  (ainfo.DataBuffer[ainfo.DataBuffer[2]+5]<>$16) then checkerror:=true;

  if checkerror then //校验错误。
  begin
       Exit;
  end;

  result := 1 ;
end;