rtl-sdr/src/librtlsdr.c

/*
 * rtl-sdr, turns your Realtek RTL2832 based DVB dongle into a SDR receiver
 * Copyright (C) 2012 by Steve Markgraf <steve@steve-m.de>
 * Copyright (C) 2012 by Dimitri Stolnikov <horiz0n@gmx.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <errno.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#ifndef _WIN32
#include <unistd.h>
#define min(a, b) (((a) < (b)) ? (a) : (b))
#endif

#include <libusb.h>

/*
 * All libusb callback functions should be marked with the LIBUSB_CALL macro
 * to ensure that they are compiled with the same calling convention as libusb.
 *
 * If the macro isn't available in older libusb versions, we simply define it.
 */
#ifndef LIBUSB_CALL
#define LIBUSB_CALL
#endif

/* two raised to the power of n */
#define TWO_POW(n)		((double)(1ULL<<(n)))

#include "rtl-sdr.h"
#include "tuner_e4k.h"
#include "tuner_fc0012.h"
#include "tuner_fc0013.h"
#include "tuner_fc2580.h"
#include "tuner_r820t.h"

typedef struct rtlsdr_tuner_iface {
	/* tuner interface */
	int (*init)(void *);
	int (*exit)(void *);
	int (*set_freq)(void *, uint32_t freq /* Hz */);
	int (*set_bw)(void *, int bw /* Hz */);
	int (*set_gain)(void *, int gain /* tenth dB */);
	int (*set_if_gain)(void *, int stage, int gain /* tenth dB */);
	int (*set_gain_mode)(void *, int manual);
} rtlsdr_tuner_iface_t;

enum rtlsdr_async_status {
	RTLSDR_INACTIVE = 0,
	RTLSDR_CANCELING,
	RTLSDR_RUNNING
};

struct rtlsdr_dev {
	libusb_context *ctx;
	struct libusb_device_handle *devh;
	uint32_t xfer_buf_num;
	uint32_t xfer_buf_len;
	struct libusb_transfer **xfer;
	unsigned char **xfer_buf;
	rtlsdr_read_async_cb_t cb;
	void *cb_ctx;
	enum rtlsdr_async_status async_status;
	/* rtl demod context */
	uint32_t rate; /* Hz */
	uint32_t rtl_xtal; /* Hz */
	int direct_sampling;
	/* tuner context */
	enum rtlsdr_tuner tuner_type;
	rtlsdr_tuner_iface_t *tuner;
	uint32_t tun_xtal; /* Hz */
	uint32_t freq; /* Hz */
	uint32_t offs_freq; /* Hz */
	int corr; /* ppm */
	int gain; /* tenth dB */
	struct e4k_state e4k_s;
};

void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val);

/* generic tuner interface functions, shall be moved to the tuner implementations */
int e4000_init(void *dev) {
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
	devt->e4k_s.i2c_addr = E4K_I2C_ADDR;
	devt->e4k_s.vco.fosc = devt->tun_xtal; /* no need to correct it here */
	devt->e4k_s.rtl_dev = dev;
	return e4k_init(&devt->e4k_s);
}
int e4000_exit(void *dev) { return 0; }
int e4000_set_freq(void *dev, uint32_t freq) {
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
	return e4k_tune_freq(&devt->e4k_s, freq);
}

int e4000_set_bw(void *dev, int bw) {
	int r = 0;
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;

	r |= e4k_if_filter_bw_set(&devt->e4k_s, E4K_IF_FILTER_MIX, bw);
	r |= e4k_if_filter_bw_set(&devt->e4k_s, E4K_IF_FILTER_RC, bw);
	r |= e4k_if_filter_bw_set(&devt->e4k_s, E4K_IF_FILTER_CHAN, bw);

	return r;
}

int e4000_set_gain(void *dev, int gain) {
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
	int mixgain = (gain > 340) ? 12 : 4;
#if 0
	int enhgain = (gain - 420);
#endif
	if(e4k_set_lna_gain(&devt->e4k_s, min(300, gain - mixgain * 10)) == -EINVAL)
		return -1;
	if(e4k_mixer_gain_set(&devt->e4k_s, mixgain) == -EINVAL)
		return -1;
#if 0 /* enhanced mixer gain seems to have no effect */
	if(enhgain >= 0)
		if(e4k_set_enh_gain(&devt->e4k_s, enhgain) == -EINVAL)
			return -1;
#endif
	return 0;
}
int e4000_set_if_gain(void *dev, int stage, int gain) {
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
	return e4k_if_gain_set(&devt->e4k_s, (uint8_t)stage, (int8_t)(gain / 10));
}
int e4000_set_gain_mode(void *dev, int manual) {
	rtlsdr_dev_t* devt = (rtlsdr_dev_t*)dev;
	return e4k_enable_manual_gain(&devt->e4k_s, manual);
}

int _fc0012_init(void *dev) { return fc0012_init(dev); }
int fc0012_exit(void *dev) { return 0; }
int fc0012_set_freq(void *dev, uint32_t freq) {
	/* select V-band/U-band filter */
	rtlsdr_set_gpio_bit(dev, 6, (freq > 300000000) ? 1 : 0);
	return fc0012_set_params(dev, freq, 6000000);
}
int fc0012_set_bw(void *dev, int bw) { return 0; }
int _fc0012_set_gain(void *dev, int gain) { return fc0012_set_gain(dev, gain); }
int fc0012_set_gain_mode(void *dev, int manual) { return 0; }

int _fc0013_init(void *dev) { return fc0013_init(dev); }
int fc0013_exit(void *dev) { return 0; }
int fc0013_set_freq(void *dev, uint32_t freq) {
	return fc0013_set_params(dev, freq, 6000000);
}
int fc0013_set_bw(void *dev, int bw) { return 0; }
int _fc0013_set_gain(void *dev, int gain) { return fc0013_set_lna_gain(dev, gain); }

int fc2580_init(void *dev) { return fc2580_Initialize(dev); }
int fc2580_exit(void *dev) { return 0; }
int _fc2580_set_freq(void *dev, uint32_t freq) {
	return fc2580_SetRfFreqHz(dev, freq);
}
int fc2580_set_bw(void *dev, int bw) { return fc2580_SetBandwidthMode(dev, 1); }
int fc2580_set_gain(void *dev, int gain) { return 0; }
int fc2580_set_gain_mode(void *dev, int manual) { return 0; }

int r820t_init(void *dev) {
	int r = R828_Init(dev);
	r820t_SetStandardMode(dev, DVB_T_6M);
	return r;
}
int r820t_exit(void *dev) { return 0; }
int r820t_set_freq(void *dev, uint32_t freq) { return r820t_SetRfFreqHz(dev, freq); }
int r820t_set_bw(void *dev, int bw) { return 0; }
int r820t_set_gain(void *dev, int gain) { return 0; }
int r820t_set_gain_mode(void *dev, int manual) { return 0; }

/* definition order must match enum rtlsdr_tuner */
static rtlsdr_tuner_iface_t tuners[] = {
	{
		NULL, NULL, NULL, NULL, NULL, NULL, NULL /* dummy for unknown tuners */
	},
	{
		e4000_init, e4000_exit,
		e4000_set_freq, e4000_set_bw, e4000_set_gain, e4000_set_if_gain,
		e4000_set_gain_mode
	},
	{
		_fc0012_init, fc0012_exit,
		fc0012_set_freq, fc0012_set_bw, _fc0012_set_gain, NULL,
		fc0012_set_gain_mode
	},
	{
		_fc0013_init, fc0013_exit,
		fc0013_set_freq, fc0013_set_bw, _fc0013_set_gain, NULL,
		fc0013_set_gain_mode
	},
	{
		fc2580_init, fc2580_exit,
		_fc2580_set_freq, fc2580_set_bw, fc2580_set_gain, NULL,
		fc2580_set_gain_mode
	},
	{
		r820t_init, r820t_exit,
		r820t_set_freq, r820t_set_bw, r820t_set_gain, NULL,
		r820t_set_gain_mode
	},
};

typedef struct rtlsdr_dongle {
	uint16_t vid;
	uint16_t pid;
	const char *name;
} rtlsdr_dongle_t;

/*
 * Please add your device here and send a patch to osmocom-sdr@lists.osmocom.org
 */
static rtlsdr_dongle_t known_devices[] = {
	{ 0x0bda, 0x2832, "Generic RTL2832U (e.g. hama nano)" },
	{ 0x0bda, 0x2838, "ezcap USB 2.0 DVB-T/DAB/FM dongle" },
	{ 0x0ccd, 0x00a9, "Terratec Cinergy T Stick Black (rev 1)" },
	{ 0x0ccd, 0x00b3, "Terratec NOXON DAB/DAB+ USB dongle (rev 1)" },
	{ 0x0ccd, 0x00b4, "Terratec NOXON DAB/DAB+ USB dongle (rev 1)" },
	{ 0x0ccd, 0x00b7, "Terratec NOXON DAB/DAB+ USB dongle (rev 1)" },
	{ 0x0ccd, 0x00c6, "Terratec NOXON DAB/DAB+ USB dongle (rev 1)" },
	{ 0x0ccd, 0x00d3, "Terratec Cinergy T Stick RC (Rev.3)" },
	{ 0x0ccd, 0x00d7, "Terratec T Stick PLUS" },
	{ 0x0ccd, 0x00e0, "Terratec NOXON DAB/DAB+ USB dongle (rev 2)" },
	{ 0x185b, 0x0620, "Compro Videomate U620F"},
	{ 0x185b, 0x0650, "Compro Videomate U650F"},
	{ 0x185b, 0x0680, "Compro Videomate U680F"},
	{ 0x1f4d, 0xa803, "Sweex DVB-T USB" },
	{ 0x1f4d, 0xb803, "GTek T803" },
	{ 0x1f4d, 0xc803, "Lifeview LV5TDeluxe" },
	{ 0x1f4d, 0xd286, "MyGica TD312" },
	{ 0x1f4d, 0xd803, "PROlectrix DV107669" },
	{ 0x1b80, 0xd398, "Zaapa ZT-MINDVBZP" },
	{ 0x1b80, 0xd3a4, "Twintech UT-40" },
	{ 0x1d19, 0x1101, "Dexatek DK DVB-T Dongle (Logilink VG0002A)" },
	{ 0x1d19, 0x1102, "Dexatek DK DVB-T Dongle (MSI DigiVox mini II V3.0)" },
	{ 0x1d19, 0x1103, "Dexatek Technology Ltd. DK 5217 DVB-T Dongle" },
	{ 0x0458, 0x707f, "Genius TVGo DVB-T03 USB dongle (Ver. B)" },
	{ 0x1b80, 0xd393, "GIGABYTE GT-U7300" },
	{ 0x1b80, 0xd394, "DIKOM USB-DVBT HD" },
	{ 0x1b80, 0xd395, "Peak 102569AGPK" },
	{ 0x1b80, 0xd39d, "SVEON STV20 DVB-T USB & FM" },
};

#define DEFAULT_BUF_NUMBER	32
#define DEFAULT_BUF_LENGTH	(16 * 32 * 512)

#define DEF_RTL_XTAL_FREQ	28800000
#define MIN_RTL_XTAL_FREQ	(DEF_RTL_XTAL_FREQ - 1000)
#define MAX_RTL_XTAL_FREQ	(DEF_RTL_XTAL_FREQ + 1000)

#define MAX_SAMP_RATE		3200000

#define CTRL_IN		(LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_IN)
#define CTRL_OUT	(LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT)
#define CTRL_TIMEOUT	300
#define BULK_TIMEOUT	0

enum usb_reg {
	USB_SYSCTL		= 0x2000,
	USB_CTRL		= 0x2010,
	USB_STAT		= 0x2014,
	USB_EPA_CFG		= 0x2144,
	USB_EPA_CTL		= 0x2148,
	USB_EPA_MAXPKT		= 0x2158,
	USB_EPA_MAXPKT_2	= 0x215a,
	USB_EPA_FIFO_CFG	= 0x2160,
};

enum sys_reg {
	DEMOD_CTL		= 0x3000,
	GPO			= 0x3001,
	GPI			= 0x3002,
	GPOE			= 0x3003,
	GPD			= 0x3004,
	SYSINTE			= 0x3005,
	SYSINTS			= 0x3006,
	GP_CFG0			= 0x3007,
	GP_CFG1			= 0x3008,
	SYSINTE_1		= 0x3009,
	SYSINTS_1		= 0x300a,
	DEMOD_CTL_1		= 0x300b,
	IR_SUSPEND		= 0x300c,
};

enum blocks {
	DEMODB			= 0,
	USBB			= 1,
	SYSB			= 2,
	TUNB			= 3,
	ROMB			= 4,
	IRB			= 5,
	IICB			= 6,
};

int rtlsdr_read_array(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint8_t *array, uint8_t len)
{
	int r;
	uint16_t index = (block << 8);

	r = libusb_control_transfer(dev->devh, CTRL_IN, 0, addr, index, array, len, CTRL_TIMEOUT);
#if 0
	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);
#endif
	return r;
}

int rtlsdr_write_array(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint8_t *array, uint8_t len)
{
	int r;
	uint16_t index = (block << 8) | 0x10;

	r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, array, len, CTRL_TIMEOUT);
#if 0
	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);
#endif
	return r;
}

int rtlsdr_i2c_write_reg(rtlsdr_dev_t *dev, uint8_t i2c_addr, uint8_t reg, uint8_t val)
{
	uint16_t addr = i2c_addr;
	uint8_t data[2];

	data[0] = reg;
	data[1] = val;
	return rtlsdr_write_array(dev, IICB, addr, (uint8_t *)&data, 2);
}

uint8_t rtlsdr_i2c_read_reg(rtlsdr_dev_t *dev, uint8_t i2c_addr, uint8_t reg)
{
	uint16_t addr = i2c_addr;
	uint8_t data = 0;

	rtlsdr_write_array(dev, IICB, addr, &reg, 1);
	rtlsdr_read_array(dev, IICB, addr, &data, 1);

	return data;
}

/* TODO clean this up again */
int e4k_reg_write(struct e4k_state *e4k, uint8_t reg, uint8_t val)
{
	return rtlsdr_i2c_write_reg((rtlsdr_dev_t*)e4k->rtl_dev, e4k->i2c_addr, reg, val);}

uint8_t e4k_reg_read(struct e4k_state *e4k, uint8_t reg)
{
	return rtlsdr_i2c_read_reg((rtlsdr_dev_t*)e4k->rtl_dev, e4k->i2c_addr, reg);
}

int rtlsdr_i2c_write(rtlsdr_dev_t *dev, uint8_t i2c_addr, uint8_t *buffer, int len)
{
	uint16_t addr = i2c_addr;

	if (!dev)
		return -1;

	return rtlsdr_write_array(dev, IICB, addr, buffer, len);
}

int rtlsdr_i2c_read(rtlsdr_dev_t *dev, uint8_t i2c_addr, uint8_t *buffer, int len)
{
	uint16_t addr = i2c_addr;

	if (!dev)
		return -1;

	return rtlsdr_read_array(dev, IICB, addr, buffer, len);
}

uint16_t rtlsdr_read_reg(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint8_t len)
{
	int r;
	unsigned char data[2];
	uint16_t index = (block << 8);
	uint16_t reg;

	r = libusb_control_transfer(dev->devh, CTRL_IN, 0, addr, index, data, len, CTRL_TIMEOUT);

	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);

	reg = (data[1] << 8) | data[0];

	return reg;
}

int rtlsdr_write_reg(rtlsdr_dev_t *dev, uint8_t block, uint16_t addr, uint16_t val, uint8_t len)
{
	int r;
	unsigned char data[2];

	uint16_t index = (block << 8) | 0x10;

	if (len == 1)
		data[0] = val & 0xff;
	else
		data[0] = val >> 8;

	data[1] = val & 0xff;

	r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, data, len, CTRL_TIMEOUT);

	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);

	return r;
}

uint16_t rtlsdr_demod_read_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, uint8_t len)
{
	int r;
	unsigned char data[2];

	uint16_t index = page;
	uint16_t reg;
	addr = (addr << 8) | 0x20;

	r = libusb_control_transfer(dev->devh, CTRL_IN, 0, addr, index, data, len, CTRL_TIMEOUT);

	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);

	reg = (data[1] << 8) | data[0];

	return reg;
}

int rtlsdr_demod_write_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, uint16_t val, uint8_t len)
{
	int r;
	unsigned char data[2];
	uint16_t index = 0x10 | page;
	addr = (addr << 8) | 0x20;

	if (len == 1)
		data[0] = val & 0xff;
	else
		data[0] = val >> 8;

	data[1] = val & 0xff;

	r = libusb_control_transfer(dev->devh, CTRL_OUT, 0, addr, index, data, len, CTRL_TIMEOUT);

	if (r < 0)
		fprintf(stderr, "%s failed with %d\n", __FUNCTION__, r);

	rtlsdr_demod_read_reg(dev, 0x0a, 0x01, 1);

	return (r == len) ? 0 : -1;
}

void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val)
{
	uint8_t r;

	gpio = 1 << gpio;
	r = rtlsdr_read_reg(dev, SYSB, GPO, 1);
	r = val ? (r | gpio) : (r & ~gpio);
	rtlsdr_write_reg(dev, SYSB, GPO, r, 1);
}

void rtlsdr_set_gpio_output(rtlsdr_dev_t *dev, uint8_t gpio)
{
	int r;
	gpio = 1 << gpio;

	r = rtlsdr_read_reg(dev, SYSB, GPD, 1);
	rtlsdr_write_reg(dev, SYSB, GPO, r & ~gpio, 1);
	r = rtlsdr_read_reg(dev, SYSB, GPOE, 1);
	rtlsdr_write_reg(dev, SYSB, GPOE, r | gpio, 1);
}

void rtlsdr_set_i2c_repeater(rtlsdr_dev_t *dev, int on)
{
	rtlsdr_demod_write_reg(dev, 1, 0x01, on ? 0x18 : 0x10, 1);
}

void rtlsdr_init_baseband(rtlsdr_dev_t *dev)
{
	unsigned int i;

	/* default FIR coefficients used for DAB/FM by the Windows driver,
	 * the DVB driver uses different ones */
	uint8_t fir_coeff[] = {
		0xca, 0xdc, 0xd7, 0xd8, 0xe0, 0xf2, 0x0e, 0x35, 0x06, 0x50,
		0x9c, 0x0d, 0x71, 0x11, 0x14, 0x71, 0x74, 0x19, 0x41, 0xa5,
	};

	/* initialize USB */
	rtlsdr_write_reg(dev, USBB, USB_SYSCTL, 0x09, 1);
	rtlsdr_write_reg(dev, USBB, USB_EPA_MAXPKT, 0x0002, 2);
	rtlsdr_write_reg(dev, USBB, USB_EPA_CTL, 0x1002, 2);

	/* poweron demod */
	rtlsdr_write_reg(dev, SYSB, DEMOD_CTL_1, 0x22, 1);
	rtlsdr_write_reg(dev, SYSB, DEMOD_CTL, 0xe8, 1);

	/* reset demod (bit 3, soft_rst) */
	rtlsdr_demod_write_reg(dev, 1, 0x01, 0x14, 1);
	rtlsdr_demod_write_reg(dev, 1, 0x01, 0x10, 1);

	/* disable spectrum inversion and adjacent channel rejection */
	rtlsdr_demod_write_reg(dev, 1, 0x15, 0x00, 1);
	rtlsdr_demod_write_reg(dev, 1, 0x16, 0x0000, 2);

	/* clear both DDC shift and IF frequency registers  */
	for (i = 0; i < 6; i++)
		rtlsdr_demod_write_reg(dev, 1, 0x16 + i, 0x00, 1);

	/* set FIR coefficients */
	for (i = 0; i < sizeof (fir_coeff); i++)
		rtlsdr_demod_write_reg(dev, 1, 0x1c + i, fir_coeff[i], 1);

	/* enable SDR mode, disable DAGC (bit 5) */
	rtlsdr_demod_write_reg(dev, 0, 0x19, 0x05, 1);

	/* init FSM state-holding register */
	rtlsdr_demod_write_reg(dev, 1, 0x93, 0xf0, 1);
	rtlsdr_demod_write_reg(dev, 1, 0x94, 0x0f, 1);

	/* disable AGC (en_dagc, bit 0) (this seems to have no effect) */
	rtlsdr_demod_write_reg(dev, 1, 0x11, 0x00, 1);

	/* disable RF and IF AGC loop */
	rtlsdr_demod_write_reg(dev, 1, 0x04, 0x00, 1);

	/* disable PID filter (enable_PID = 0) */
	rtlsdr_demod_write_reg(dev, 0, 0x61, 0x60, 1);

	/* opt_adc_iq = 0, default ADC_I/ADC_Q datapath */
	rtlsdr_demod_write_reg(dev, 0, 0x06, 0x80, 1);

	/* Enable Zero-IF mode (en_bbin bit), DC cancellation (en_dc_est),
	 * IQ estimation/compensation (en_iq_comp, en_iq_est) */
	rtlsdr_demod_write_reg(dev, 1, 0xb1, 0x1b, 1);

	/* disable 4.096 MHz clock output on pin TP_CK0 */
	rtlsdr_demod_write_reg(dev, 0, 0x0d, 0x83, 1);
}

int rtlsdr_deinit_baseband(rtlsdr_dev_t *dev)
{
	int r = 0;

	if (!dev)
		return -1;

	if (dev->tuner && dev->tuner->exit) {
		rtlsdr_set_i2c_repeater(dev, 1);
		r = dev->tuner->exit(dev); /* deinitialize tuner */
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	/* poweroff demodulator and ADCs */
	rtlsdr_write_reg(dev, SYSB, DEMOD_CTL, 0x20, 1);

	return r;
}

int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq)
{
	uint32_t rtl_xtal;
	int32_t if_freq;
	uint8_t tmp;
	int r;

	if (!dev)
		return -1;

	/* read corrected clock value */
	if (rtlsdr_get_xtal_freq(dev, &rtl_xtal, NULL))
		return -2;

	if_freq = ((freq * TWO_POW(22)) / rtl_xtal) * (-1);

	tmp = (if_freq >> 16) & 0x3f;
	r = rtlsdr_demod_write_reg(dev, 1, 0x19, tmp, 1);
	tmp = (if_freq >> 8) & 0xff;
	r |= rtlsdr_demod_write_reg(dev, 1, 0x1a, tmp, 1);
	tmp = if_freq & 0xff;
	r |= rtlsdr_demod_write_reg(dev, 1, 0x1b, tmp, 1);

	return r;
}

int rtlsdr_set_sample_freq_correction(rtlsdr_dev_t *dev, int ppm)
{
	int r = 0;
	uint8_t tmp;
	int16_t offs = ppm * (-1) * TWO_POW(24) / 1000000;

	tmp = offs & 0xff;
	r |= rtlsdr_demod_write_reg(dev, 1, 0x3f, tmp, 1);
	tmp = (offs >> 8) & 0x3f;
	r |= rtlsdr_demod_write_reg(dev, 1, 0x3e, tmp, 1);

	return r;
}

int rtlsdr_set_xtal_freq(rtlsdr_dev_t *dev, uint32_t rtl_freq, uint32_t tuner_freq)
{
	int r = 0;

	if (!dev)
		return -1;

	if (rtl_freq > 0 &&
		(rtl_freq < MIN_RTL_XTAL_FREQ || rtl_freq > MAX_RTL_XTAL_FREQ))
		return -2;

	if (rtl_freq > 0 && dev->rtl_xtal != rtl_freq) {
		dev->rtl_xtal = rtl_freq;

		/* update xtal-dependent settings */
		if (dev->rate)
			r = rtlsdr_set_sample_rate(dev, dev->rate);
	}

	if (dev->tun_xtal != tuner_freq) {
		if (0 == tuner_freq)
			dev->tun_xtal = dev->rtl_xtal;
		else
			dev->tun_xtal = tuner_freq;

		/* read corrected clock value into e4k structure */
		if (rtlsdr_get_xtal_freq(dev, NULL, &dev->e4k_s.vco.fosc))
			return -3;

		/* update xtal-dependent settings */
		if (dev->freq)
			r = rtlsdr_set_center_freq(dev, dev->freq);
	}

	return r;
}

int rtlsdr_get_xtal_freq(rtlsdr_dev_t *dev, uint32_t *rtl_freq, uint32_t *tuner_freq)
{
	if (!dev)
		return -1;

	#define APPLY_PPM_CORR(val,ppm) (((val) * (1.0 + (ppm) / 1e6)))

	if (rtl_freq)
		*rtl_freq = (uint32_t) APPLY_PPM_CORR(dev->rtl_xtal, dev->corr);

	if (tuner_freq)
		*tuner_freq = (uint32_t) APPLY_PPM_CORR(dev->tun_xtal, dev->corr);

	return 0;
}

int rtlsdr_get_usb_strings(rtlsdr_dev_t *dev, char *manufact, char *product,
			    char *serial)
{
	struct libusb_device_descriptor dd;
	libusb_device *device = NULL;
	const int buf_max = 256;
	int r = 0;

	if (!dev || !dev->devh)
		return -1;

	device = libusb_get_device(dev->devh);

	r = libusb_get_device_descriptor(device, &dd);
	if (r < 0)
		return -1;

	if (manufact) {
		memset(manufact, 0, buf_max);
		libusb_get_string_descriptor_ascii(dev->devh, dd.iManufacturer,
						   (unsigned char *)manufact,
						   buf_max);
	}

	if (product) {
		memset(product, 0, buf_max);
		libusb_get_string_descriptor_ascii(dev->devh, dd.iProduct,
						   (unsigned char *)product,
						   buf_max);
	}

	if (serial) {
		memset(serial, 0, buf_max);
		libusb_get_string_descriptor_ascii(dev->devh, dd.iSerialNumber,
						   (unsigned char *)serial,
						   buf_max);
	}

	return 0;
}

int rtlsdr_set_center_freq(rtlsdr_dev_t *dev, uint32_t freq)
{
	int r = -1;

	if (!dev || !dev->tuner)
		return -1;

	if (dev->direct_sampling) {
		r = rtlsdr_set_if_freq(dev, freq);
	} else if (dev->tuner && dev->tuner->set_freq) {
		rtlsdr_set_i2c_repeater(dev, 1);
		r = dev->tuner->set_freq(dev, freq - dev->offs_freq);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	if (!r)
		dev->freq = freq;
	else
		dev->freq = 0;

	return r;
}

uint32_t rtlsdr_get_center_freq(rtlsdr_dev_t *dev)
{
	if (!dev)
		return 0;

	return dev->freq;
}

int rtlsdr_set_freq_correction(rtlsdr_dev_t *dev, int ppm)
{
	int r = 0;

	if (!dev)
		return -1;

	if (dev->corr == ppm)
		return -2;

	dev->corr = ppm;

	r |= rtlsdr_set_sample_freq_correction(dev, ppm);

	/* read corrected clock value into e4k structure */
	if (rtlsdr_get_xtal_freq(dev, NULL, &dev->e4k_s.vco.fosc))
		return -3;

	if (dev->freq) /* retune to apply new correction value */
		r |= rtlsdr_set_center_freq(dev, dev->freq);

	return r;
}

int rtlsdr_get_freq_correction(rtlsdr_dev_t *dev)
{
	if (!dev)
		return 0;

	return dev->corr;
}

enum rtlsdr_tuner rtlsdr_get_tuner_type(rtlsdr_dev_t *dev)
{
	if (!dev)
		return RTLSDR_TUNER_UNKNOWN;

	return dev->tuner_type;
}

int rtlsdr_get_tuner_gains(rtlsdr_dev_t *dev, int *gains)
{
	/* all gain values are expressed in tenths of a dB */
	const int e4k_gains[] = { -10, 15, 40, 65, 90, 115, 140, 165, 190, 215,
				  240, 290, 340, 420 };
	const int fc0012_gains[] = { -99, -40, 71, 179, 192 };
	const int fc0013_gains[] = { -99, -73, -65, -63, -60, -58, -54, 58, 61,
				       63, 65, 67, 68, 70, 71, 179, 181, 182,
				       184, 186, 188, 191, 197 };
	const int fc2580_gains[] = { 0 /* no gain values */ };
	const int r820t_gains[] = { 0 /* no gain values */ };
	const int unknown_gains[] = { 0 /* no gain values */ };

	int *ptr = NULL;
	int len = 0;

	if (!dev)
		return -1;

	switch (dev->tuner_type) {
	case RTLSDR_TUNER_E4000:
		ptr = (int *)e4k_gains; len = sizeof(e4k_gains);
		break;
	case RTLSDR_TUNER_FC0012:
		ptr = (int *)fc0012_gains; len = sizeof(fc0012_gains);
		break;
	case RTLSDR_TUNER_FC0013:
		ptr = (int *)fc0013_gains; len = sizeof(fc0013_gains);
		break;
	case RTLSDR_TUNER_FC2580:
		ptr = (int *)fc2580_gains; len = sizeof(fc2580_gains);
		break;
	case RTLSDR_TUNER_R820T:
		ptr = (int *)r820t_gains; len = sizeof(r820t_gains);
		break;
	default:
		ptr = (int *)unknown_gains; len = sizeof(unknown_gains);
		break;
	}

	if (!gains) { /* no buffer provided, just return the count */
		return len / sizeof(int);
	} else {
		if (len)
			memcpy(gains, ptr, len);

		return len / sizeof(int);
	}
}

int rtlsdr_set_tuner_gain(rtlsdr_dev_t *dev, int gain)
{
	int r = 0;

	if (!dev || !dev->tuner)
		return -1;

	if (dev->tuner->set_gain) {
		rtlsdr_set_i2c_repeater(dev, 1);
		r = dev->tuner->set_gain((void *)dev, gain);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	if (!r)
		dev->gain = gain;
	else
		dev->gain = 0;

	return r;
}

int rtlsdr_get_tuner_gain(rtlsdr_dev_t *dev)
{
	if (!dev)
		return 0;

	return dev->gain;
}

int rtlsdr_set_tuner_if_gain(rtlsdr_dev_t *dev, int stage, int gain)
{
	int r = 0;

	if (!dev || !dev->tuner)
		return -1;

	if (dev->tuner->set_if_gain) {
		rtlsdr_set_i2c_repeater(dev, 1);
		r = dev->tuner->set_if_gain(dev, stage, gain);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	return r;
}

int rtlsdr_set_tuner_gain_mode(rtlsdr_dev_t *dev, int mode)
{
	int r = 0;

	if (!dev || !dev->tuner)
		return -1;

	if (dev->tuner->set_gain_mode) {
		rtlsdr_set_i2c_repeater(dev, 1);
		r = dev->tuner->set_gain_mode((void *)dev, mode);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	return r;
}

int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate)
{
	int r = 0;
	uint16_t tmp;
	uint32_t rsamp_ratio;
	double real_rate;
	uint32_t rtl_freq = dev->rtl_xtal;

	if (!dev)
		return -1;

	/* check for the maximum rate the resampler supports */
	if (samp_rate > MAX_SAMP_RATE)
		samp_rate = MAX_SAMP_RATE;

	rsamp_ratio = (rtl_freq * TWO_POW(22)) / samp_rate;
	rsamp_ratio &= ~3;

	real_rate = (rtl_freq * TWO_POW(22)) / rsamp_ratio;

	if ( ((double)samp_rate) != real_rate )
		fprintf(stderr, "Exact sample rate is: %f Hz\n", real_rate);

	if (dev->tuner && dev->tuner->set_bw) {
		rtlsdr_set_i2c_repeater(dev, 1);
		dev->tuner->set_bw(dev, (int)real_rate);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	dev->rate = (uint32_t)real_rate;

	tmp = (rsamp_ratio >> 16);
	r |= rtlsdr_demod_write_reg(dev, 1, 0x9f, tmp, 2);
	tmp = rsamp_ratio & 0xffff;
	r |= rtlsdr_demod_write_reg(dev, 1, 0xa1, tmp, 2);

	r |= rtlsdr_set_sample_freq_correction(dev, dev->corr);

	/* reset demod (bit 3, soft_rst) */
	r |= rtlsdr_demod_write_reg(dev, 1, 0x01, 0x14, 1);
	r |= rtlsdr_demod_write_reg(dev, 1, 0x01, 0x10, 1);

	return r;
}

uint32_t rtlsdr_get_sample_rate(rtlsdr_dev_t *dev)
{
	if (!dev)
		return 0;

	return dev->rate;
}

int rtlsdr_set_testmode(rtlsdr_dev_t *dev, int on)
{
	if (!dev)
		return -1;

	return rtlsdr_demod_write_reg(dev, 0, 0x19, on ? 0x03 : 0x05, 1);
}

int rtlsdr_set_agc_mode(rtlsdr_dev_t *dev, int on)
{
	if (!dev)
		return -1;

	return rtlsdr_demod_write_reg(dev, 0, 0x19, on ? 0x25 : 0x05, 1);
}

int rtlsdr_set_direct_sampling(rtlsdr_dev_t *dev, int on)
{
	int r = 0;

	if (!dev)
		return -1;

	if (on) {
		if (dev->tuner && dev->tuner->exit) {
			rtlsdr_set_i2c_repeater(dev, 1);
			r = dev->tuner->exit(dev);
			rtlsdr_set_i2c_repeater(dev, 0);
		}

		/* disable Zero-IF mode */
		r |= rtlsdr_demod_write_reg(dev, 1, 0xb1, 0x1a, 1);

		/* disable spectrum inversion */
		r |= rtlsdr_demod_write_reg(dev, 1, 0x15, 0x00, 1);

		/* only enable In-phase ADC input */
		r |= rtlsdr_demod_write_reg(dev, 0, 0x08, 0x4d, 1);

		/* swap I and Q ADC, this allows to select between two inputs */
		r |= rtlsdr_demod_write_reg(dev, 0, 0x06, (on > 1) ? 0x90 : 0x80, 1);

		fprintf(stderr, "Enabled direct sampling mode, input %i\n", on);
		dev->direct_sampling = on;
	} else {
		if (dev->tuner && dev->tuner->init) {
			rtlsdr_set_i2c_repeater(dev, 1);
			r |= dev->tuner->init(dev);
			rtlsdr_set_i2c_repeater(dev, 0);
		}

		if (dev->tuner_type == RTLSDR_TUNER_R820T) {
			r |= rtlsdr_set_if_freq(dev, R820T_IF_FREQ);

			/* enable spectrum inversion */
			r |= rtlsdr_demod_write_reg(dev, 1, 0x15, 0x01, 1);
		} else {
			r |= rtlsdr_set_if_freq(dev, 0);

			/* enable In-phase + Quadrature ADC input */
			r |= rtlsdr_demod_write_reg(dev, 0, 0x08, 0xcd, 1);

			/* Enable Zero-IF mode */
			r |= rtlsdr_demod_write_reg(dev, 1, 0xb1, 0x1b, 1);
		}

		/* opt_adc_iq = 0, default ADC_I/ADC_Q datapath */
		r |= rtlsdr_demod_write_reg(dev, 0, 0x06, 0x80, 1);

		fprintf(stderr, "Disabled direct sampling mode\n");
		dev->direct_sampling = 0;
	}

	r |= rtlsdr_set_center_freq(dev, dev->freq);

	return r;
}

int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on)
{
	int r = 0;

	if (!dev)
		return -1;

	if (dev->tuner_type == RTLSDR_TUNER_R820T)
		return -2;

	/* based on keenerds 1/f noise measurements */
	dev->offs_freq = on ? ((dev->rate / 2) * 170 / 100) : 0;
	r |= rtlsdr_set_if_freq(dev, dev->offs_freq);

	if (dev->tuner && dev->tuner->set_bw) {
		rtlsdr_set_i2c_repeater(dev, 1);
		dev->tuner->set_bw(dev, on ? (2 * dev->offs_freq) : dev->rate);
		rtlsdr_set_i2c_repeater(dev, 0);
	}

	r |= rtlsdr_set_center_freq(dev, dev->freq);

	return r;
}

static rtlsdr_dongle_t *find_known_device(uint16_t vid, uint16_t pid)
{
	unsigned int i;
	rtlsdr_dongle_t *device = NULL;

	for (i = 0; i < sizeof(known_devices)/sizeof(rtlsdr_dongle_t); i++ ) {
		if (known_devices[i].vid == vid && known_devices[i].pid == pid) {
			device = &known_devices[i];
			break;
		}
	}

	return device;
}

uint32_t rtlsdr_get_device_count(void)
{
	int i;
	libusb_context *ctx;
	libusb_device **list;
	uint32_t device_count = 0;
	struct libusb_device_descriptor dd;
	ssize_t cnt;

	libusb_init(&ctx);

	cnt = libusb_get_device_list(ctx, &list);

	for (i = 0; i < cnt; i++) {
		libusb_get_device_descriptor(list[i], &dd);

		if (find_known_device(dd.idVendor, dd.idProduct))
			device_count++;
	}

	libusb_free_device_list(list, 1);

	libusb_exit(ctx);

	return device_count;
}

const char *rtlsdr_get_device_name(uint32_t index)
{
	int i;
	libusb_context *ctx;
	libusb_device **list;
	struct libusb_device_descriptor dd;
	rtlsdr_dongle_t *device = NULL;
	uint32_t device_count = 0;
	ssize_t cnt;

	libusb_init(&ctx);

	cnt = libusb_get_device_list(ctx, &list);

	for (i = 0; i < cnt; i++) {
		libusb_get_device_descriptor(list[i], &dd);

		device = find_known_device(dd.idVendor, dd.idProduct);

		if (device) {
			device_count++;

			if (index == device_count - 1)
				break;
		}
	}

	libusb_free_device_list(list, 1);

	libusb_exit(ctx);

	if (device)
		return device->name;
	else
		return "";
}

int rtlsdr_get_device_usb_strings(uint32_t index, char *manufact,
				   char *product, char *serial)
{
	int r = -2;
	int i;
	libusb_context *ctx;
	libusb_device **list;
	struct libusb_device_descriptor dd;
	rtlsdr_dongle_t *device = NULL;
	rtlsdr_dev_t devt;
	uint32_t device_count = 0;
	ssize_t cnt;

	libusb_init(&ctx);

	cnt = libusb_get_device_list(ctx, &list);

	for (i = 0; i < cnt; i++) {
		libusb_get_device_descriptor(list[i], &dd);

		device = find_known_device(dd.idVendor, dd.idProduct);

		if (device) {
			device_count++;

			if (index == device_count - 1) {
				r = libusb_open(list[i], &devt.devh);
				if (!r) {
					r = rtlsdr_get_usb_strings(&devt,
								   manufact,
								   product,
								   serial);
					libusb_close(devt.devh);
				}
				break;
			}
		}
	}

	libusb_free_device_list(list, 1);

	libusb_exit(ctx);

	return r;
}

int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t index)
{
	int r;
	int i;
	libusb_device **list;
	rtlsdr_dev_t *dev = NULL;
	libusb_device *device = NULL;
	uint32_t device_count = 0;
	struct libusb_device_descriptor dd;
	uint8_t reg;
	ssize_t cnt;

	dev = malloc(sizeof(rtlsdr_dev_t));
	if (NULL == dev)
		return -ENOMEM;

	memset(dev, 0, sizeof(rtlsdr_dev_t));

	libusb_init(&dev->ctx);

	cnt = libusb_get_device_list(dev->ctx, &list);

	for (i = 0; i < cnt; i++) {
		device = list[i];

		libusb_get_device_descriptor(list[i], &dd);

		if (find_known_device(dd.idVendor, dd.idProduct)) {
			device_count++;
		}

		if (index == device_count - 1)
			break;

		device = NULL;
	}

	if (!device) {
		r = -1;
		goto err;
	}

	r = libusb_open(device, &dev->devh);
	if (r < 0) {
		libusb_free_device_list(list, 1);
		fprintf(stderr, "usb_open error %d\n", r);
		goto err;
	}

	libusb_free_device_list(list, 1);

	r = libusb_claim_interface(dev->devh, 0);
	if (r < 0) {
		fprintf(stderr, "usb_claim_interface error %d\n", r);
		goto err;
	}

	dev->rtl_xtal = DEF_RTL_XTAL_FREQ;

	rtlsdr_init_baseband(dev);

	/* Probe tuners */
	rtlsdr_set_i2c_repeater(dev, 1);

	reg = rtlsdr_i2c_read_reg(dev, E4K_I2C_ADDR, E4K_CHECK_ADDR);
	if (reg == E4K_CHECK_VAL) {
		fprintf(stderr, "Found Elonics E4000 tuner\n");
		dev->tuner_type = RTLSDR_TUNER_E4000;
		goto found;
	}

	reg = rtlsdr_i2c_read_reg(dev, FC0013_I2C_ADDR, FC0013_CHECK_ADDR);
	if (reg == FC0013_CHECK_VAL) {
		fprintf(stderr, "Found Fitipower FC0013 tuner\n");
		dev->tuner_type = RTLSDR_TUNER_FC0013;
		goto found;
	}

	reg = rtlsdr_i2c_read_reg(dev, R820T_I2C_ADDR, R820T_CHECK_ADDR);
	if (reg == R820T_CHECK_VAL) {
		fprintf(stderr, "Found Rafael Micro R820T tuner\n");
		dev->tuner_type = RTLSDR_TUNER_R820T;

		/* disable Zero-IF mode */
		rtlsdr_demod_write_reg(dev, 1, 0xb1, 0x1a, 1);

		/* only enable In-phase ADC input */
		rtlsdr_demod_write_reg(dev, 0, 0x08, 0x4d, 1);

		/* the R820T uses 3.57 MHz IF for the DVB-T 6 MHz mode, and
		 * 4.57 MHz for the 8 MHz mode */
		rtlsdr_set_if_freq(dev, R820T_IF_FREQ);

		/* enable spectrum inversion */
		rtlsdr_demod_write_reg(dev, 1, 0x15, 0x01, 1);

		goto found;
	}

	/* initialise GPIOs */
	rtlsdr_set_gpio_output(dev, 5);

	/* reset tuner before probing */
	rtlsdr_set_gpio_bit(dev, 5, 1);
	rtlsdr_set_gpio_bit(dev, 5, 0);

	reg = rtlsdr_i2c_read_reg(dev, FC2580_I2C_ADDR, FC2580_CHECK_ADDR);
	if ((reg & 0x7f) == FC2580_CHECK_VAL) {
		fprintf(stderr, "Found FCI 2580 tuner\n");
		dev->tuner_type = RTLSDR_TUNER_FC2580;
		goto found;
	}

	reg = rtlsdr_i2c_read_reg(dev, FC0012_I2C_ADDR, FC0012_CHECK_ADDR);
	if (reg == FC0012_CHECK_VAL) {
		fprintf(stderr, "Found Fitipower FC0012 tuner\n");
		rtlsdr_set_gpio_output(dev, 6);
		dev->tuner_type = RTLSDR_TUNER_FC0012;
		goto found;
	}

found:
	if (dev->tuner_type == RTLSDR_TUNER_UNKNOWN) {
		fprintf(stderr, "No supported tuner found\n");
		rtlsdr_set_direct_sampling(dev, 1);
	}

	dev->tuner = &tuners[dev->tuner_type];
	dev->tun_xtal = dev->rtl_xtal; /* use the rtl clock value by default */

	if (dev->tuner->init)
		r = dev->tuner->init(dev);

	rtlsdr_set_i2c_repeater(dev, 0);

	*out_dev = dev;

	return 0;
err:
	if (dev) {
		if (dev->ctx)
			libusb_exit(dev->ctx);

		free(dev);
	}

	return r;
}

int rtlsdr_close(rtlsdr_dev_t *dev)
{
	if (!dev)
		return -1;

	/* block until all async operations have been completed (if any) */
	while (RTLSDR_INACTIVE != dev->async_status) {
#ifdef _WIN32
		Sleep(1);
#else
		usleep(1000);
#endif
	}

	rtlsdr_deinit_baseband(dev);

	libusb_release_interface(dev->devh, 0);
	libusb_close(dev->devh);

	libusb_exit(dev->ctx);

	free(dev);

	return 0;
}

int rtlsdr_reset_buffer(rtlsdr_dev_t *dev)
{
	if (!dev)
		return -1;

	rtlsdr_write_reg(dev, USBB, USB_EPA_CTL, 0x1002, 2);
	rtlsdr_write_reg(dev, USBB, USB_EPA_CTL, 0x0000, 2);

	return 0;
}

int rtlsdr_read_sync(rtlsdr_dev_t *dev, void *buf, int len, int *n_read)
{
	if (!dev)
		return -1;

	return libusb_bulk_transfer(dev->devh, 0x81, buf, len, n_read, BULK_TIMEOUT);
}

static void LIBUSB_CALL _libusb_callback(struct libusb_transfer *xfer)
{
	rtlsdr_dev_t *dev = (rtlsdr_dev_t *)xfer->user_data;

	if (LIBUSB_TRANSFER_COMPLETED == xfer->status) {
		if (dev->cb)
			dev->cb(xfer->buffer, xfer->actual_length, dev->cb_ctx);

		libusb_submit_transfer(xfer); /* resubmit transfer */
	} else if (LIBUSB_TRANSFER_CANCELLED == xfer->status) {
		/* nothing to do */
	} else {
		/*fprintf(stderr, "transfer status: %d\n", xfer->status);*/
	}
}

int rtlsdr_wait_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, void *ctx)
{
	return rtlsdr_read_async(dev, cb, ctx, 0, 0);
}

static int _rtlsdr_alloc_async_buffers(rtlsdr_dev_t *dev)
{
	unsigned int i;

	if (!dev)
		return -1;

	if (!dev->xfer) {
		dev->xfer = malloc(dev->xfer_buf_num *
				   sizeof(struct libusb_transfer *));

		for(i = 0; i < dev->xfer_buf_num; ++i)
			dev->xfer[i] = libusb_alloc_transfer(0);
	}

	if (!dev->xfer_buf) {
		dev->xfer_buf = malloc(dev->xfer_buf_num *
					   sizeof(unsigned char *));

		for(i = 0; i < dev->xfer_buf_num; ++i)
			dev->xfer_buf[i] = malloc(dev->xfer_buf_len);
	}

	return 0;
}

static int _rtlsdr_free_async_buffers(rtlsdr_dev_t *dev)
{
	unsigned int i;

	if (!dev)
		return -1;

	if (dev->xfer) {
		for(i = 0; i < dev->xfer_buf_num; ++i) {
			if (dev->xfer[i]) {
				libusb_free_transfer(dev->xfer[i]);
			}
		}

		free(dev->xfer);
		dev->xfer = NULL;
	}

	if (dev->xfer_buf) {
		for(i = 0; i < dev->xfer_buf_num; ++i) {
			if (dev->xfer_buf[i])
				free(dev->xfer_buf[i]);
		}

		free(dev->xfer_buf);
		dev->xfer_buf = NULL;
	}

	return 0;
}

int rtlsdr_read_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, void *ctx,
			  uint32_t buf_num, uint32_t buf_len)
{
	unsigned int i;
	int r = 0;
	struct timeval tv = { 1, 0 };
	enum rtlsdr_async_status next_status = RTLSDR_INACTIVE;

	if (!dev)
		return -1;

	if (RTLSDR_INACTIVE != dev->async_status)
		return -2;

	dev->async_status = RTLSDR_RUNNING;

	dev->cb = cb;
	dev->cb_ctx = ctx;

	if (buf_num > 0)
		dev->xfer_buf_num = buf_num;
	else
		dev->xfer_buf_num = DEFAULT_BUF_NUMBER;

	if (buf_len > 0 && buf_len % 512 == 0) /* len must be multiple of 512 */
		dev->xfer_buf_len = buf_len;
	else
		dev->xfer_buf_len = DEFAULT_BUF_LENGTH;

	_rtlsdr_alloc_async_buffers(dev);

	for(i = 0; i < dev->xfer_buf_num; ++i) {
		libusb_fill_bulk_transfer(dev->xfer[i],
					  dev->devh,
					  0x81,
					  dev->xfer_buf[i],
					  dev->xfer_buf_len,
					  _libusb_callback,
					  (void *)dev,
					  BULK_TIMEOUT);

		libusb_submit_transfer(dev->xfer[i]);
	}

	while (RTLSDR_INACTIVE != dev->async_status) {
		r = libusb_handle_events_timeout(dev->ctx, &tv);
		if (r < 0) {
			/*fprintf(stderr, "handle_events returned: %d\n", r);*/
			if (r == LIBUSB_ERROR_INTERRUPTED) /* stray signal */
				continue;
			break;
		}

		if (RTLSDR_CANCELING == dev->async_status) {
			next_status = RTLSDR_INACTIVE;

			if (!dev->xfer)
				break;

			for(i = 0; i < dev->xfer_buf_num; ++i) {
				if (!dev->xfer[i])
					continue;

				if (LIBUSB_TRANSFER_CANCELLED !=
						dev->xfer[i]->status) {
					libusb_cancel_transfer(dev->xfer[i]);
					next_status = RTLSDR_CANCELING;
				}
			}

			if (RTLSDR_INACTIVE == next_status)
				break;
		}
	}

	_rtlsdr_free_async_buffers(dev);

	dev->async_status = next_status;

	return r;
}

int rtlsdr_cancel_async(rtlsdr_dev_t *dev)
{
	if (!dev)
		return -1;

	/* if streaming, try to cancel gracefully */
	if (RTLSDR_RUNNING == dev->async_status) {
		dev->async_status = RTLSDR_CANCELING;
		return 0;
	}

	/* if called while in pending state, change the state forcefully */
	if (RTLSDR_INACTIVE != dev->async_status) {
		dev->async_status = RTLSDR_INACTIVE;
		return 0;
	}

	return -2;
}

uint32_t rtlsdr_get_tuner_clock(void *dev)
{
	uint32_t tuner_freq;

	if (!dev)
		return 0;

	/* read corrected clock value */
	if (rtlsdr_get_xtal_freq((rtlsdr_dev_t *)dev, NULL, &tuner_freq))
		return 0;

	return tuner_freq;
}

int rtlsdr_i2c_write_fn(void *dev, uint8_t addr, uint8_t *buf, int len)
{
	if (dev)
		return rtlsdr_i2c_write(((rtlsdr_dev_t *)dev), addr, buf, len);

	return -1;
}

int rtlsdr_i2c_read_fn(void *dev, uint8_t addr, uint8_t *buf, int len)
{
	if (dev)
		return rtlsdr_i2c_read(((rtlsdr_dev_t *)dev), addr, buf, len);

	return -1;
}