Degrade performance in IQ data capture by IIO

Analog Device provides two reference design to capture the data from the AD9361 reference design:

1. github.com/.../iio_fm_radio.c

2. github.com/.../ad9361-iiostream.c

I made the modification in ad9361-iiostream (in attachment). sample processing (as in iio_fm_radio ) was added, tx part was commented.

I observe (see attached pictures) 7 times degrade performance (CPU usage 74% vs 11%) for ad9361-iiostream.

Some of my investigation:

iio_fm_radio uses system calls for capturing the data. ad9361-iiostream uses iio_buffer functions. I thought that functionality should be the same but iio_fm_radio has 4 buffers by 1MB of data and processing each buffer individually. It seems ad9361-iiostream also creates 4 buffers because nbytes_rx always returns 4MB of data (nbytes_rx = iio_buffer_refill(rxbuf);).

Could someone explain how I can get better performance (close to iio_fm_demod) with ad9361-iiostream ?

iiostream_fm_radio.c

/*
 * libiio - AD9361 IIO streaming example
 *
 * Copyright (C) 2014 IABG mbH
 * Author: Michael Feilen <feilen_at_iabg.de>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 **/

#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>

#ifdef __APPLE__
#include <iio/iio.h>
#else
#include <iio.h>
#endif

/* helper macros */
#define MHZ(x) ((long long)(x*1000000.0 + .5))
#define GHZ(x) ((long long)(x*1000000000.0 + .5))

#define ASSERT(expr) { \
	if (!(expr)) { \
		(void) fprintf(stderr, "assertion failed (%s:%d)\n", __FILE__, __LINE__); \
		(void) abort(); \
	} \
}

/* RX is input, TX is output */
enum iodev { RX, TX };

/* common RX and TX streaming params */
struct stream_cfg {
	long long bw_hz; // Analog banwidth in Hz
	long long fs_hz; // Baseband sample rate in Hz
	long long lo_hz; // Local oscillator frequency in Hz
	const char* rfport; // Port name
};

/* static scratch mem for strings */
static char tmpstr[64];

/* IIO structs required for streaming */
static struct iio_context *ctx   = NULL;
static struct iio_channel *rx0_i = NULL;
static struct iio_channel *rx0_q = NULL;
// static struct iio_channel *tx0_i = NULL;
// static struct iio_channel *tx0_q = NULL;
static struct iio_buffer  *rxbuf = NULL;
// static struct iio_buffer  *txbuf = NULL;

static bool stop;

/* Min and max are used for automatic gain control and DC offset control */
static int min = 0xfffffff;
static int max = -0xfffffff;

#define DECIMATION_FACTOR 48
#define AUDIO_SAMPLE_RATE 48000

/* cleanup and exit */
static void shutdown()
{
	printf("* Destroying buffers\n");
	if (rxbuf) { iio_buffer_destroy(rxbuf); }
	// if (txbuf) { iio_buffer_destroy(txbuf); }

	printf("* Disabling streaming channels\n");
	if (rx0_i) { iio_channel_disable(rx0_i); }
	if (rx0_q) { iio_channel_disable(rx0_q); }
	// if (tx0_i) { iio_channel_disable(tx0_i); }
	// if (tx0_q) { iio_channel_disable(tx0_q); }

	printf("* Destroying context\n");
	if (ctx) { iio_context_destroy(ctx); }
	exit(0);
}

static void handle_sig(int sig)
{
	printf("Waiting for process to finish...\n");
	stop = true;
}

/* check return value of attr_write function */
static void errchk(int v, const char* what) {
	 if (v < 0) { fprintf(stderr, "Error %d writing to channel \"%s\"\nvalue may not be supported.\n", v, what); shutdown(); }
}

/* write attribute: long long int */
static void wr_ch_lli(struct iio_channel *chn, const char* what, long long val)
{
	errchk(iio_channel_attr_write_longlong(chn, what, val), what);
}

/* write attribute: string */
static void wr_ch_str(struct iio_channel *chn, const char* what, const char* str)
{
	errchk(iio_channel_attr_write(chn, what, str), what);
}

/* helper function generating channel names */
static char* get_ch_name(const char* type, int id)
{
	snprintf(tmpstr, sizeof(tmpstr), "%s%d", type, id);
	return tmpstr;
}

/* returns ad9361 phy device */
static struct iio_device* get_ad9361_phy(struct iio_context *ctx)
{
	struct iio_device *dev =  iio_context_find_device(ctx, "ad9361-phy");
	ASSERT(dev && "No ad9361-phy found");
	return dev;
}

/* finds AD9361 streaming IIO devices */
static bool get_ad9361_stream_dev(struct iio_context *ctx, enum iodev d, struct iio_device **dev)
{
	switch (d) {
	case TX: *dev = iio_context_find_device(ctx, "cf-ad9361-dds-core-lpc"); return *dev != NULL;
	case RX: *dev = iio_context_find_device(ctx, "cf-ad9361-lpc");  return *dev != NULL;
	default: ASSERT(0); return false;
	}
}

/* finds AD9361 streaming IIO channels */
static bool get_ad9361_stream_ch(struct iio_context *ctx, enum iodev d, struct iio_device *dev, int chid, struct iio_channel **chn)
{
	*chn = iio_device_find_channel(dev, get_ch_name("voltage", chid), d == TX);
	if (!*chn)
		*chn = iio_device_find_channel(dev, get_ch_name("altvoltage", chid), d == TX);
	return *chn != NULL;
}

/* finds AD9361 phy IIO configuration channel with id chid */
static bool get_phy_chan(struct iio_context *ctx, enum iodev d, int chid, struct iio_channel **chn)
{
	switch (d) {
	case RX: *chn = iio_device_find_channel(get_ad9361_phy(ctx), get_ch_name("voltage", chid), false); return *chn != NULL;
	case TX: *chn = iio_device_find_channel(get_ad9361_phy(ctx), get_ch_name("voltage", chid), true);  return *chn != NULL;
	default: ASSERT(0); return false;
	}
}

/* finds AD9361 local oscillator IIO configuration channels */
static bool get_lo_chan(struct iio_context *ctx, enum iodev d, struct iio_channel **chn)
{
	switch (d) {
	 // LO chan is always output, i.e. true
	case RX: *chn = iio_device_find_channel(get_ad9361_phy(ctx), get_ch_name("altvoltage", 0), true); return *chn != NULL;
	case TX: *chn = iio_device_find_channel(get_ad9361_phy(ctx), get_ch_name("altvoltage", 1), true); return *chn != NULL;
	default: ASSERT(0); return false;
	}
}

/* applies streaming configuration through IIO */
bool cfg_ad9361_streaming_ch(struct iio_context *ctx, struct stream_cfg *cfg, enum iodev type, int chid)
{
	struct iio_channel *chn = NULL;

	// Configure phy and lo channels
	printf("* Acquiring AD9361 phy channel %d\n", chid);
	if (!get_phy_chan(ctx, type, chid, &chn)) {	return false; }
	wr_ch_str(chn, "rf_port_select",     cfg->rfport);
	wr_ch_lli(chn, "rf_bandwidth",       cfg->bw_hz);
	wr_ch_lli(chn, "sampling_frequency", cfg->fs_hz);

	// Configure LO channel
	printf("* Acquiring AD9361 %s lo channel\n", type == TX ? "TX" : "RX");
	if (!get_lo_chan(ctx, type, &chn)) { return false; }
	wr_ch_lli(chn, "frequency", cfg->lo_hz);
	return true;
}

/* simple configuration and streaming */
int main (int argc, char **argv)
{
	// Streaming devices
	// struct iio_device *tx;
	struct iio_device *rx;

	// RX and TX sample counters
	size_t nrx = 0;
	// size_t ntx = 0;

	// Stream configurations
	struct stream_cfg rxcfg;
	// struct stream_cfg txcfg;

	// Listen to ctrl+c and ASSERT
	signal(SIGINT, handle_sig);

	// RX stream config
	rxcfg.bw_hz = MHZ(2);   // 2 MHz rf bandwidth
	rxcfg.fs_hz = MHZ(2.5);   // 2.5 MS/s rx sample rate
	rxcfg.lo_hz = GHZ(2.5); // 2.5 GHz rf frequency
	rxcfg.rfport = "A_BALANCED"; // port A (select for rf freq.)

	// TX stream config
	// txcfg.bw_hz = MHZ(1.5); // 1.5 MHz rf bandwidth
	// txcfg.fs_hz = MHZ(2.5);   // 2.5 MS/s tx sample rate
	// txcfg.lo_hz = GHZ(2.5); // 2.5 GHz rf frequency
	// txcfg.rfport = "A"; // port A (select for rf freq.)

	printf("* Acquiring IIO context\n");
	ASSERT((ctx = iio_create_default_context()) && "No context");
	ASSERT(iio_context_get_devices_count(ctx) > 0 && "No devices");

	printf("* Acquiring AD9361 streaming devices\n");
	// ASSERT(get_ad9361_stream_dev(ctx, TX, &tx) && "No tx dev found");
	ASSERT(get_ad9361_stream_dev(ctx, RX, &rx) && "No rx dev found");

	printf("* Configuring AD9361 for streaming\n");
	ASSERT(cfg_ad9361_streaming_ch(ctx, &rxcfg, RX, 0) && "RX port 0 not found");
	// ASSERT(cfg_ad9361_streaming_ch(ctx, &txcfg, TX, 0) && "TX port 0 not found");

	printf("* Initializing AD9361 IIO streaming channels\n");
	ASSERT(get_ad9361_stream_ch(ctx, RX, rx, 0, &rx0_i) && "RX chan i not found");
	ASSERT(get_ad9361_stream_ch(ctx, RX, rx, 1, &rx0_q) && "RX chan q not found");
	// ASSERT(get_ad9361_stream_ch(ctx, TX, tx, 0, &tx0_i) && "TX chan i not found");
	// ASSERT(get_ad9361_stream_ch(ctx, TX, tx, 1, &tx0_q) && "TX chan q not found");

	printf("* Enabling IIO streaming channels\n");
	iio_channel_enable(rx0_i);
	iio_channel_enable(rx0_q);
	// iio_channel_enable(tx0_i);
	// iio_channel_enable(tx0_q);

	printf("* Creating non-cyclic IIO buffers with 1 MiS\n");
	rxbuf = iio_device_create_buffer(rx, 1024*1024, false);
	if (!rxbuf) {
		perror("Could not create RX buffer");
		shutdown();
	}
	// txbuf = iio_device_create_buffer(tx, 1024*1024, false);
	// if (!txbuf) {
		// perror("Could not create TX buffer");
		// shutdown();
	// }

  int new_min, new_max;
	long i[3], q[3], di, dq;
	long long sample = 0;
	unsigned int j;
	unsigned int sub = 4;
	unsigned int x = 0;
	unsigned int n = 0;
	short *sample_buffer;
	size_t num_bytes, offset;
	int ret;
  sample_buffer = malloc(1024*1024*4 / DECIMATION_FACTOR / 2);
	printf("* Starting IO streaming (press CTRL+C to cancel)\n");
	while (!stop)
	{
		ssize_t nbytes_rx, nbytes_tx;
		char *p_dat, *p_end;
		ptrdiff_t p_inc;

		// Schedule TX buffer
		// nbytes_tx = iio_buffer_push(txbuf);
		// if (nbytes_tx < 0) { printf("Error pushing buf %d\n", (int) nbytes_tx); shutdown(); }

		// Refill RX buffer
		nbytes_rx = iio_buffer_refill(rxbuf);
		if (nbytes_rx < 0) { printf("Error refilling buf %d\n",(int) nbytes_rx); shutdown(); }
    
    x = 0;
    n = 0;
    new_min = 0xfffffff;
	  new_max = -0xfffffff;

		// READ: Get pointers to RX buf and read IQ from RX buf port 0
		p_inc = iio_buffer_step(rxbuf);
		p_end = iio_buffer_end(rxbuf);
		for (p_dat = (char *)iio_buffer_first(rxbuf, rx0_i); p_dat < p_end; p_dat += p_inc) {
			// Example: swap I and Q
			i[0] = ((int16_t*)p_dat)[0]; // Real (I)
			q[0] = ((int16_t*)p_dat)[1]; // Imag (Q)

      di = i[0] - i[2];
      dq = q[0] - q[2];

      sample += (i[1] * dq - q[1] * di);

      i[2] = i[1];
      q[2] = q[1];
      i[1] = i[0];
      q[1] = q[0];

      x += sub;
      if (x >= DECIMATION_FACTOR) {
        x = 0;
        sample /= (DECIMATION_FACTOR / sub);

        if (sample < new_min)
          new_min = sample;
        if (sample > new_max)
          new_max = sample;

        if (min >= max)
          continue;

        sample -= (max - min) / 2;
        sample = sample * 0x1fff / (max - min);
        if (sample > 0x1fff)
          sample = 0x1fff;
        else if(sample < -0x1fff)
          sample = -0x1fff;

        sample_buffer[n] = sample;	
        n++;
        sample = 0;
      }
		}
    
    min = new_min;
	  max = new_max;

  	if (n == 0)
      continue;
  
    num_bytes = 2 * n;
    offset = 0;

    do {
      ret = write(STDOUT_FILENO, sample_buffer + offset, num_bytes);
      if (ret <= 0)
        break;
      num_bytes -= ret;
      offset += ret;
    } while (num_bytes);
      
    

    if (ret == 0) {
      fprintf(stderr, "Failed to write samples to stdout: EOF\n");
      return -1;
    }

    if (ret == -1) {
      perror("Failed to write samples to stdout");
      return -1;
    }
    
		// WRITE: Get pointers to TX buf and write IQ to TX buf port 0
		// p_inc = iio_buffer_step(txbuf);
		// p_end = iio_buffer_end(txbuf);
		// for (p_dat = (char *)iio_buffer_first(txbuf, tx0_i); p_dat < p_end; p_dat += p_inc) {
			// // Example: fill with zeros
			// // 12-bit sample needs to be MSB alligned so shift by 4
			// // https://wiki.analog.com/resources/eval/user-guides/ad-fmcomms2-ebz/software/basic_iq_datafiles#binary_format
			// ((int16_t*)p_dat)[0] = 0 << 4; // Real (I)
			// ((int16_t*)p_dat)[1] = 0 << 4; // Imag (Q)
		// }

		// Sample counter increment and status output
		// nrx += nbytes_rx / iio_device_get_sample_size(rx);
		// ntx += nbytes_tx / iio_device_get_sample_size(tx);
		// printf("\tRX %8.2f MSmp, TX %8.2f MSmp\n", nrx/1e6, ntx/1e6);
	}

	shutdown();
  free(sample_buffer);

	return 0;
}  

Makefile

DESTDIR=/usr/local
CFLAGS=-Wall -Werror -std=gnu99 -D_GNU_SOURCE -O2

all: iiostream_fm_radio

iiostream_fm_radio: iiostream_fm_radio.c
	cc -Wall   -c -o iiostream_fm_radio.o iiostream_fm_radio.c
	cc -o iiostream_fm_radio iiostream_fm_radio.o  -liio

clean:
	rm -f iiostream_fm_radio iiostream_fm_radio.o 



Add sources
[edited by: kpiterrr at 11:14 AM (GMT 0) on 14 Aug 2020]