Format the binary file as Motorola S-Records records and return
        them as a string.

        `number_of_data_bytes` is the number of data bytes in each
        record.

        `address_length_bits` is the number of address bits in each
        record.

        >>> print(binfile.as_srec())
        S32500000100214601360121470136007EFE09D219012146017E17C20001FF5F16002148011973
        S32500000120194E79234623965778239EDA3F01B2CA3F0156702B5E712B722B73214601342199
        S5030002FA

def as_srec(self, number_of_data_bytes=32, address_length_bits=32):
        """Format the binary file as Motorola S-Records records and return
        them as a string.

        `number_of_data_bytes` is the number of data bytes in each
        record.

        `address_length_bits` is the number of address bits in each
        record.

        >>> print(binfile.as_srec())
        S32500000100214601360121470136007EFE09D219012146017E17C20001FF5F16002148011973
        S32500000120194E79234623965778239EDA3F01B2CA3F0156702B5E712B722B73214601342199
        S5030002FA

        """

        header = []

        if self._header is not None:
            record = pack_srec('0', 0, len(self._header), self._header)
            header.append(record)

        type_ = str((address_length_bits // 8) - 1)

        if type_ not in '123':
            raise Error("expected data record type 1..3, but got {}".format(
                type_))

        data = [pack_srec(type_, address, len(data), data)
                for address, data in self._segments.chunks(number_of_data_bytes)]
        number_of_records = len(data)

        if number_of_records <= 0xffff:
            footer = [pack_srec('5', number_of_records, 0, None)]
        elif number_of_records <= 0xffffff:
            footer = [pack_srec('6', number_of_records, 0, None)]
        else:
            raise Error('too many records {}'.format(number_of_records))

        # Add the execution start address.
        if self.execution_start_address is not None:
            if type_ == '1':
                record = pack_srec('9', self.execution_start_address, 0, None)
            elif type_ == '2':
                record = pack_srec('8', self.execution_start_address, 0, None)
            else:
                record = pack_srec('7', self.execution_start_address, 0, None)

            footer.append(record)

        return '\n'.join(header + data + footer) + '\n'