AS3933 receive data

void AS3933_read_data(uint8_t addr, uint8_t reg, uint8_t len, uint8_t *data)
{
	uint8_t i = 0;
	uint8_t tmp;

	if(len > 1)
	{
		tmp = reg | 0x80;
	}
	else
	{
		tmp = reg;
	}

	set_CSN_low();
	spi_transfer(SPI_WRITE_BYTE);
	spi_transfer(addr);
	spi_transfer(tmp);

	for(i = 0; i < len; i++)
	{
		data[i] = spi_transfer(0xFF);
	}

	set_CSN_high();
}