plsql and vb

[dreams]

Hi every one,
I don't know how to retrieve the result from plsql into vb :(
my plsql function is:

create or replace function log_in (name in int)
return int
is
x int;
begin
x :=1;
return x;
end log_in;

my vb.net code is:
con.ConnectionString = "Driver={Microsoft ODBC for Oracle};Server=localhost;Uid=hr;Pwd=hr"
Dim sql As String = "declare y1 int ;begin y1 := log_in(2); end;"
Dim cmd As New Odbc.OdbcCommand(sql, con)
cmd.CommandType = CommandType.StoredProcedure
con.Open()
Dim rv As OdbcParameter
rv = cmd.CreateParameter()
rv.Direction = ParameterDirection.ReturnValue
rv.DbType = DbType.Int16
cmd.Parameters.Add(rv)
Dim ret As Integer = cmd.ExecuteScalar()
MsgBox(ret)
con.close()

the output is always 0 instead of 1 !!!
could any one help me :)