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adaptive.c
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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// adaptive.c: adaptive gain control
//
// Copyright (c) 2021 FlightAware, LLC
//
// This file is free software: you may copy, redistribute 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 file 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 "dump1090.h"
#include "adaptive.h"
//
// gain limits
//
static int adaptive_gain_min;
static int adaptive_gain_max;
// gain steps relative to current gain
static float adaptive_gain_up_db;
static float adaptive_gain_down_db;
//
// block handling
//
// 1 block = approx 1 second of samples. Control updates are done at the end of each block only.
// Each block is made up of an integer number of subblocks (currently 20)
//
// 1 subblock = approx 50ms of samples. Duty cycle decisions are made at the subblock level;
// either the whole subblock is processed, or the whole subblock is skipped.
// Each subblock is made up of an integer number of windows (currently 1250)
//
// 1 window = approx 40us of samples. Burst measurements are made by counting samples within each window.
//
// All three levels are aligned, i.e. every block boundary is also a subblock boundary;
// every subblock boundary is also a window boundary.
static const unsigned adaptive_subblocks_per_block = 20; // subblocks per block
static unsigned adaptive_subblocks_remaining; // subblocks remaining in the current block
// Duty cycle is expressed as N/D
// where N = adaptive_subblbock_dutycycle_N = adaptive_subblocks_per_block * Modes.adaptive_duty_cycle
// and D = adaptive_subblocks_dutycycle_D = adaptive_subblocks_per_block
//
// i.e. within each block, there are exactly N active subblocks out of D total subblocks
//
// The active subblocks are distributed evenly across the block by increasing a counter by N on each
// subblock, modulo D, and marking the subblock as active each time the counter rolls over.
static unsigned adaptive_subblock_dutycycle_N; // subblock duty cycle numerator N
// stretch gcc doesn't like this as a separate const
#define adaptive_subblock_dutycycle_D adaptive_subblocks_per_block
static unsigned adaptive_subblock_dutycycle_counter; // subblock duty cycle counter (modulo D)
static bool adaptive_subblock_active; // is the current subblock active i.e. samples should be processed, not skipped?
static unsigned adaptive_samples_per_subblock; // samples per subblock
static unsigned adaptive_subblock_samples_remaining; // samples remaining in the current subblock
static unsigned adaptive_samples_per_window; // samples per window
void adaptive_init();
void adaptive_update(uint16_t *buf, unsigned length, struct modesMessage *decoded);
static void adaptive_update_subblock(uint16_t *buf, unsigned length, struct modesMessage *decoded);
static void adaptive_end_of_block();
static void adaptive_control_update();
//
// burst handling
//
static unsigned adaptive_burst_window_remaining; // samples remaining in the current burst window
static unsigned adaptive_burst_window_counter; // loud samples seen in current burst window
static unsigned adaptive_burst_runlength; // consecutive loud burst windows seen
static unsigned adaptive_burst_block_loud_undecoded; // loud undecoded bursts seen in this block so far
static unsigned adaptive_burst_block_loud_decoded; // loud decoded messages seen in this block so far
static double adaptive_burst_loud_undecoded_smoothed; // smoothed rate of loud misdecodes per block
static double adaptive_burst_loud_decoded_smoothed; // smoothed rate of loud successful decodes per block
static unsigned adaptive_burst_change_timer; // countdown inhibiting control after changing gain
static double adaptive_burst_loud_threshold; // current signal level threshold for a "loud decode"
static unsigned adaptive_burst_loud_blocks = 0; // consecutive blocks with loud rate
static unsigned adaptive_burst_quiet_blocks = 0; // consecutive blocks with quiet rate
static void adaptive_burst_update(uint16_t *buf, unsigned length);
static void adaptive_burst_skip(unsigned length);
static unsigned adaptive_burst_count_samples(uint16_t *buf, unsigned n);
static void adaptive_burst_scan_windows(uint16_t *buf, unsigned windows);
static void adaptive_burst_end_of_window(unsigned counter);
static void adaptive_burst_end_of_block();
//
// noise floor measurement (adaptive dynamic range)
//
static unsigned *adaptive_range_radix; // radix-sort buckets for current block
static unsigned adaptive_range_radix_counter; // sum of all radix-sort buckets (= number of samples sorted)
static double adaptive_range_smoothed; // smoothed noise floor estimate, dBFS
static enum { RANGE_SCAN_IDLE, RANGE_SCAN_UP, RANGE_SCAN_DOWN, RANGE_RESCAN_UP, RANGE_RESCAN_DOWN } adaptive_range_state = RANGE_SCAN_UP;
static unsigned adaptive_range_change_timer; // countdown inhibiting control after changing gain
static unsigned adaptive_range_rescan_timer; // countdown to next upwards gain reprobe
static int adaptive_range_gain_limit; // probed maximum gain step with acceptable dynamic range
static void adaptive_range_update(uint16_t *buf, unsigned length);
static void adaptive_range_end_of_block();
// Try to change the SDR gain to 'step' and tell the user about it,
// with 'why' as the reason to show. Return true if the gain actually changed.
static bool adaptive_set_gain(int step, const char *why)
{
if (step < adaptive_gain_min)
step = adaptive_gain_min;
if (step > adaptive_gain_max)
step = adaptive_gain_max;
int current_gain = sdrGetGain();
if (current_gain == step)
return false;
fprintf(stderr, "adaptive: changing gain from %.1fdB (step %d) to %.1fdB (step %d) because: %s\n",
sdrGetGainDb(current_gain), current_gain, sdrGetGainDb(step), step, why);
int new_gain = sdrSetGain(step);
bool changed = (current_gain != new_gain);
if (changed)
++Modes.stats_current.adaptive_gain_changes;
return changed;
}
// Update internal state to reflect a gain change
// (usually after adaptive_set_gain returns true, but also called during init)
static void adaptive_gain_changed()
{
int new_gain = sdrGetGain();
adaptive_gain_up_db = sdrGetGainDb(new_gain + 1) - sdrGetGainDb(new_gain);
adaptive_gain_down_db = sdrGetGainDb(new_gain) - sdrGetGainDb(new_gain - 1);
double loud_threshold_dbfs = 0 - adaptive_gain_up_db - 3.0;
adaptive_burst_loud_threshold = pow(10, loud_threshold_dbfs / 10.0);
adaptive_range_change_timer = Modes.adaptive_range_change_delay;
adaptive_burst_change_timer = Modes.adaptive_burst_change_delay;
adaptive_burst_loud_blocks = 0;
adaptive_burst_quiet_blocks = 0;
}
// External init entry point
void adaptive_init()
{
int maxgain = sdrGetMaxGain();
// If the SDR doesn't support gain control, disable ourselves
if (maxgain < 0) {
if (Modes.adaptive_burst_control || Modes.adaptive_range_control) {
fprintf(stderr, "warning: adaptive gain control requested, but SDR gain control not available, ignored.\n");
}
Modes.adaptive_burst_control = false;
Modes.adaptive_range_control = false;
}
// If we're disabled, do nothing
if (!Modes.adaptive_burst_control && !Modes.adaptive_range_control)
return;
// Set up window, subblock, and block sizes
// Look for 40us bursts
adaptive_samples_per_window = Modes.sample_rate / 25000;
// Use ~50ms subblocks; ensure it's an exact multiple of window size
adaptive_samples_per_subblock = adaptive_samples_per_window * 1250;
adaptive_subblocks_remaining = adaptive_subblocks_per_block;
adaptive_subblock_samples_remaining = adaptive_samples_per_subblock;
adaptive_subblock_active = false;
float N = roundf(adaptive_subblock_dutycycle_D * Modes.adaptive_duty_cycle);
if (N <= 0)
N = 1;
if (N > adaptive_subblock_dutycycle_D)
N = adaptive_subblock_dutycycle_D;
fprintf(stderr, "adaptive: using %.0f%% duty cycle\n", 100.0 * N / adaptive_subblock_dutycycle_D);
adaptive_subblock_dutycycle_N = (unsigned)N;
adaptive_burst_window_remaining = adaptive_samples_per_window;
adaptive_burst_window_counter = 0;
adaptive_range_radix = calloc(sizeof(unsigned), 65536);
adaptive_range_state = RANGE_RESCAN_UP;
// select and enforce gain limits
for (adaptive_gain_min = 0; adaptive_gain_min < maxgain; ++adaptive_gain_min) {
if (sdrGetGainDb(adaptive_gain_min) >= Modes.adaptive_min_gain_db)
break;
}
for (adaptive_gain_max = maxgain; adaptive_gain_max > adaptive_gain_min; --adaptive_gain_max) {
if (sdrGetGainDb(adaptive_gain_max) <= Modes.adaptive_max_gain_db)
break;
}
fprintf(stderr, "adaptive: enabled adaptive gain control with gain limits %.1fdB (step %d) .. %.1fdB (step %d)\n",
sdrGetGainDb(adaptive_gain_min), adaptive_gain_min, sdrGetGainDb(adaptive_gain_max), adaptive_gain_max);
if (Modes.adaptive_range_control)
fprintf(stderr, "adaptive: enabled dynamic range control, target dynamic range %.1fdB\n", Modes.adaptive_range_target);
if (Modes.adaptive_burst_control)
fprintf(stderr, "adaptive: enabled burst control\n");
adaptive_set_gain(sdrGetGain(), "constraining gain to adaptive gain limits");
adaptive_gain_changed();
adaptive_range_gain_limit = sdrGetGain();
}
// Feed some samples into the adaptive system. Any number of samples might be passed in.
void adaptive_update(uint16_t *buf, unsigned length, struct modesMessage *decoded)
{
if (!Modes.adaptive_burst_control && !Modes.adaptive_range_control)
return;
// process complete subblocks
while (length >= adaptive_subblock_samples_remaining) {
if (adaptive_subblock_active)
adaptive_update_subblock(buf, adaptive_subblock_samples_remaining, decoded);
buf += adaptive_subblock_samples_remaining;
length -= adaptive_subblock_samples_remaining;
adaptive_subblock_samples_remaining = adaptive_samples_per_subblock;
adaptive_subblock_dutycycle_counter += adaptive_subblock_dutycycle_N;
if (adaptive_subblock_dutycycle_counter >= adaptive_subblock_dutycycle_D) {
adaptive_subblock_dutycycle_counter -= adaptive_subblock_dutycycle_D;
adaptive_subblock_active = true;
} else {
adaptive_subblock_active = false;
// fake a quiet window to reset any existing run
adaptive_burst_end_of_window(0);
}
if (!--adaptive_subblocks_remaining) {
// Block completed, do a control update
adaptive_subblocks_remaining = adaptive_subblocks_per_block;
adaptive_end_of_block();
}
}
// process final samples that don't complete a subblock
if (length > 0) {
if (adaptive_subblock_active)
adaptive_update_subblock(buf, length, decoded);
adaptive_subblock_samples_remaining -= length;
}
}
// Feed some samples into the adaptive system. The samples are guaranteed to not cross a subblock boundary.
// The samples should be processsed (i.e. duty cycle is in the active part)
static void adaptive_update_subblock(uint16_t *buf, unsigned length, struct modesMessage *decoded)
{
if (decoded) {
if (/* decoded->msgbits == 112 && */ decoded->signalLevel >= adaptive_burst_loud_threshold)
++adaptive_burst_block_loud_decoded;
adaptive_burst_skip(length);
} else {
adaptive_burst_update(buf, length);
adaptive_range_update(buf, length);
}
}
// Burst measurement: ignore the next 'length' samples (they are a successfully decoded message)
static void adaptive_burst_skip(unsigned length)
{
if (!Modes.adaptive_burst_control)
return;
// first window
if (length < adaptive_burst_window_remaining) {
// partial fill
adaptive_burst_window_remaining -= length;
return;
}
// skip remainder of first window, dispatch it
adaptive_burst_end_of_window(adaptive_burst_window_counter);
length -= adaptive_burst_window_remaining;
// skip remaining windows, dispatch them
unsigned windows = length / adaptive_samples_per_window;
unsigned samples = windows * adaptive_samples_per_window;
while (windows--)
adaptive_burst_end_of_window(0);
length -= samples;
// final partial window
adaptive_burst_window_counter = 0;
adaptive_burst_window_remaining = adaptive_samples_per_window - length;
}
// Burst measurement: process 'length' samples from 'buf', look for loud bursts;
// the samples might cross burst window boundaries;
// the samples will not cross a block boundary.
static void adaptive_burst_update(uint16_t *buf, unsigned length)
{
if (!Modes.adaptive_burst_control)
return;
// first window
if (length < adaptive_burst_window_remaining) {
// partial fill
adaptive_burst_window_counter += adaptive_burst_count_samples(buf, length);
adaptive_burst_window_remaining -= length;
return;
}
// complete fill of first partial window
unsigned n = adaptive_burst_window_remaining;
unsigned counter = adaptive_burst_window_counter + adaptive_burst_count_samples(buf, n);
adaptive_burst_end_of_window(counter);
buf += n;
length -= n;
// remaining windows
unsigned windows = length / adaptive_samples_per_window;
unsigned samples = windows * adaptive_samples_per_window;
adaptive_burst_scan_windows(buf, windows);
buf += samples;
length -= samples;
// final partial window
adaptive_burst_window_counter = adaptive_burst_count_samples(buf, length);
adaptive_burst_window_remaining = adaptive_samples_per_window - length;
}
// Burst measurement: process 'windows' complete burst windows starting at 'buf';
// 'buf' is aligned to the start of a burst window
static void adaptive_burst_scan_windows(uint16_t *buf, unsigned windows)
{
while (windows--) {
unsigned counter = adaptive_burst_count_samples(buf, adaptive_samples_per_window);
buf += adaptive_samples_per_window;
adaptive_burst_end_of_window(counter);
}
}
// Burst measurement: process 'n' samples from 'buf', look for loud samples;
// the samples are guaranteed not to cross window boundaries;
// return the number of loud samples seen
static inline unsigned adaptive_burst_count_samples(uint16_t *buf, unsigned n)
{
unsigned counter;
starch_count_above_u16(buf, n, 46395 /* -3dBFS */, &counter);
return counter;
}
// Burst measurement: we reached the end of a burst window with 'counter'
// loud samples seen, handle that window.
static void adaptive_burst_end_of_window(unsigned counter)
{
if (counter > adaptive_samples_per_window / 4) {
// This window is loud, extend any existing run of loud windows
++adaptive_burst_runlength;
} else {
// Quiet window. If we saw a run of loud windows >= 80us long, count
// that as a candidate for an over-amplified message that was
// not decoded.
if (adaptive_burst_runlength >= 2 && adaptive_burst_runlength <= 5)
++adaptive_burst_block_loud_undecoded;
adaptive_burst_runlength = 0;
}
}
// Noise measurement: process 'length' samples from 'buf'.
// The samples will not cross a block boundary.
static void adaptive_range_update(uint16_t *buf, unsigned length)
{
if (!Modes.adaptive_range_control)
return;
adaptive_range_radix_counter += length;
while (length--) {
// do a very simple radix sort of sample magnitudes
// so we can later find the Nth percentile value
++adaptive_range_radix[buf[0]];
++buf;
}
}
// Noise measurement: we reached the end of a block, update
// our noise estimate
static void adaptive_range_end_of_block()
{
if (!Modes.adaptive_range_control)
return;
unsigned n = 0, i = 0;
// measure Nth percentile magnitude
unsigned count_n = adaptive_range_radix_counter * Modes.adaptive_range_percentile / 100;
while (i < 65536 && n <= count_n)
n += adaptive_range_radix[i++];
uint16_t percentile_n = i - 1;
// maintain an EMA of the Nth percentile
adaptive_range_smoothed = adaptive_range_smoothed * (1 - Modes.adaptive_range_alpha) + percentile_n * Modes.adaptive_range_alpha;
// .. report to stats in dBFS
if (adaptive_range_smoothed > 0) {
Modes.stats_current.adaptive_noise_dbfs = 20 * log10(adaptive_range_smoothed / 65536.0);
} else {
Modes.stats_current.adaptive_noise_dbfs = 0;
}
// reset radix sort for the next block
memset(adaptive_range_radix, 0, 65536 * sizeof(unsigned));
adaptive_range_radix_counter = 0;
}
// Burst measurement: we reached the end of a block, update our burst rate estimate
static void adaptive_burst_end_of_block()
{
if (!Modes.adaptive_burst_control)
return;
// scale rates based on the actual duty cycle fraction
// (e.g. if we are only inspecting 2/5 of samples, then scale the rate by 5/2)
double scale = (double)adaptive_subblock_dutycycle_D / adaptive_subblock_dutycycle_N;
// maintain an EMA of the number of undecoded loud bursts seen per block
Modes.stats_current.adaptive_loud_undecoded += adaptive_burst_block_loud_undecoded;
adaptive_burst_loud_undecoded_smoothed = adaptive_burst_loud_undecoded_smoothed * (1 - Modes.adaptive_burst_alpha) + scale * adaptive_burst_block_loud_undecoded * Modes.adaptive_burst_alpha;
adaptive_burst_block_loud_undecoded = 0;
// maintain an EMA of the number of decoded, but loud, messages seen per block
Modes.stats_current.adaptive_loud_decoded += adaptive_burst_block_loud_decoded;
adaptive_burst_loud_decoded_smoothed = adaptive_burst_loud_decoded_smoothed * (1 - Modes.adaptive_burst_alpha) + scale * adaptive_burst_block_loud_decoded * Modes.adaptive_burst_alpha;
adaptive_burst_block_loud_decoded = 0;
}
void flush_stats(uint64_t now);
static void adaptive_increase_gain(const char *why)
{
if (adaptive_set_gain(sdrGetGain() + 1, why))
adaptive_gain_changed();
}
static void adaptive_decrease_gain(const char *why)
{
if (adaptive_set_gain(sdrGetGain() - 1, why))
adaptive_gain_changed();
}
// Adaptive gain: we reached a block boundary. Update measurements and act on them.
static void adaptive_end_of_block()
{
adaptive_range_end_of_block();
adaptive_burst_end_of_block();
adaptive_control_update();
Modes.stats_current.adaptive_valid = true;
Modes.stats_current.adaptive_range_gain_limit = adaptive_range_gain_limit;
int current = sdrGetGain();
if (current >= 0)
++Modes.stats_current.adaptive_gain_seconds[current < STATS_GAIN_COUNT ? current : STATS_GAIN_COUNT-1];
}
static void adaptive_control_update()
{
// votes for what to do with the gain
// "gain_not_up" overlaps somewhat with "gain_down", but they are not identical;
// burst control may want to prevent gain from increasing, but not necessarily
// decrease gain.
bool gain_up = false;
const char *gain_up_reason = NULL;
bool gain_down = false;
const char *gain_down_reason = NULL;
bool gain_not_up = false;
int current_gain = sdrGetGain();
if (adaptive_burst_change_timer)
--adaptive_burst_change_timer;
if (adaptive_range_change_timer > 0)
--adaptive_range_change_timer;
if (adaptive_range_rescan_timer > 0)
--adaptive_range_rescan_timer;
if (Modes.adaptive_burst_control && !adaptive_burst_change_timer) {
if (adaptive_burst_loud_undecoded_smoothed > Modes.adaptive_burst_loud_rate) {
adaptive_burst_quiet_blocks = 0;
++adaptive_burst_loud_blocks;
} else if (adaptive_burst_loud_decoded_smoothed < Modes.adaptive_burst_quiet_rate) {
adaptive_burst_loud_blocks = 0;
++adaptive_burst_quiet_blocks;
} else {
adaptive_burst_loud_blocks = 0;
adaptive_burst_quiet_blocks = 0;
}
if (adaptive_burst_loud_blocks >= Modes.adaptive_burst_loud_runlength) {
// we need to reduce gain (further)
gain_down = gain_not_up = true;
gain_down_reason = "high rate of loud undecoded messages";
// if we're currently doing a downward scan, reducing gain further may confuse it;
// stop that scan and restart it once we are no longer in a reduced-gain state
if (adaptive_range_state == RANGE_SCAN_DOWN || adaptive_range_state == RANGE_RESCAN_DOWN) {
adaptive_range_state = RANGE_SCAN_IDLE;
adaptive_range_rescan_timer = 0;
}
} else if (adaptive_burst_quiet_blocks < Modes.adaptive_burst_quiet_runlength) {
// we're OK at the current gain, but should not increase it
gain_not_up = true;
} else if (current_gain < adaptive_range_gain_limit) {
// we're OK at the current gain, and can increase gain to the previously discovered
// dynamic range limit
gain_up = true;
gain_up_reason = "low loud message rate and gain below dynamic range limit";
}
}
if (Modes.adaptive_range_control && !adaptive_range_change_timer) {
float available_range = -20 * log10(adaptive_range_smoothed / 65536.0);
// allow the gain limit to increase if this gain setting is acceptable
// (decreasing the limit is done separately depending on the current state as we make slightly different decisions in IDLE
// to provide hysteresis)
if (available_range >= Modes.adaptive_range_target && current_gain > adaptive_range_gain_limit) {
adaptive_range_gain_limit = current_gain;
}
switch (adaptive_range_state) {
case RANGE_SCAN_UP:
case RANGE_RESCAN_UP:
if (available_range < Modes.adaptive_range_target) {
// Current gain fails to meet our target. Switch to downward scanning.
fprintf(stderr, "adaptive: available dynamic range (%.1fdB) < required dynamic range (%.1fdB), switching to downward scan\n", available_range, Modes.adaptive_range_target);
gain_down = gain_not_up = true;
gain_down_reason = "probing dynamic range gain lower bound";
adaptive_range_state = (adaptive_range_state == RANGE_RESCAN_UP ? RANGE_RESCAN_DOWN : RANGE_SCAN_DOWN);
if (adaptive_range_gain_limit >= current_gain) {
adaptive_range_gain_limit = current_gain - 1;
}
break;
}
if (sdrGetGain() >= adaptive_gain_max) {
// We have reached our upper gain limit
fprintf(stderr, "adaptive: reached upper gain limit, halting dynamic range scan here\n");
adaptive_range_state = RANGE_SCAN_IDLE;
adaptive_range_rescan_timer = Modes.adaptive_range_rescan_delay;
break;
}
// This gain step is OK and we have more to try, try the next gain step up.
// (But if burst detection has inhibited increasing gain, don't do anything yet, just try again next block)
if (!gain_not_up) {
fprintf(stderr, "adaptive: available dynamic range (%.1fdB) >= required dynamic range (%.1fdB), continuing upward scan\n", available_range, Modes.adaptive_range_target);
gain_up = true;
gain_up_reason = "probing dynamic range gain upper bound";
}
break;
case RANGE_SCAN_DOWN:
case RANGE_RESCAN_DOWN:
if (available_range >= Modes.adaptive_range_target) {
// Current gain meets our target; we are done with the scan.
fprintf(stderr, "adaptive: available dynamic range (%.1fdB) >= required dynamic range (%.1fdB), stopping downwards scan here\n", available_range, Modes.adaptive_range_target);
adaptive_range_state = RANGE_SCAN_IDLE;
adaptive_range_rescan_timer = (adaptive_range_state == RANGE_SCAN_DOWN ? Modes.adaptive_range_scan_delay : Modes.adaptive_range_rescan_delay);
break;
}
if (adaptive_range_gain_limit >= current_gain) {
adaptive_range_gain_limit = current_gain - 1;
}
if (sdrGetGain() <= adaptive_gain_min) {
fprintf(stderr, "adaptive: reached lower gain limit, halting dynamic range scan here\n");
adaptive_range_state = RANGE_SCAN_IDLE;
adaptive_range_rescan_timer = Modes.adaptive_range_rescan_delay;
break;
}
// This gain step is too loud and we have more to try, try the next gain step down
fprintf(stderr, "adaptive: available dynamic range (%.1fdB) < required dynamic range (%.1fdB), continuing downwards scan\n", available_range, Modes.adaptive_range_target);
gain_down = gain_not_up = true;
gain_down_reason = "probing dynamic range gain lower bound";
break;
case RANGE_SCAN_IDLE:
// Look for increased noise that could be compensated for by decreasing gain.
// Do this even if we're waiting to rescan or if burst control is also active
if (available_range + adaptive_gain_down_db / 2 < Modes.adaptive_range_target && sdrGetGain() > adaptive_gain_min) {
fprintf(stderr, "adaptive: available dynamic range (%.1fdB) + half gain step down (%.1fdB) < required dynamic range (%.1fdB), starting downward scan\n",
available_range, adaptive_gain_down_db / 2, Modes.adaptive_range_target);
if (adaptive_range_gain_limit >= current_gain) {
adaptive_range_gain_limit = current_gain - 1;
}
adaptive_range_state = RANGE_SCAN_DOWN;
gain_down = gain_not_up = true;
gain_down_reason = "dynamic range fell below target value";
break;
}
// Infrequently consider increasing gain to handle the case where we've selected a too-low gain where the noise floor is dominated by noise unrelated to the gain setting.
// But don't do this while burst control is preventing gain increases.
if (!adaptive_range_rescan_timer && !gain_not_up) {
if (available_range >= Modes.adaptive_range_target && sdrGetGain() < adaptive_gain_max) {
fprintf(stderr, "adaptive: start periodic scan for acceptable dynamic range at increased gain\n");
gain_up = true;
gain_up_reason = "periodic re-probing of dynamic range gain upper bound";
adaptive_range_state = RANGE_RESCAN_UP;
break;
}
// Nothing to do for a while.
adaptive_range_rescan_timer = Modes.adaptive_range_rescan_delay;
}
break;
default:
fprintf(stderr, "adaptive: in a weird state (%u), trying to fix it\n", (unsigned) adaptive_range_state);
adaptive_range_state = RANGE_SCAN_IDLE;
adaptive_range_rescan_timer = Modes.adaptive_range_rescan_delay;
break;
}
}
// now actually perform any gain changes
if (gain_down)
adaptive_decrease_gain(gain_down_reason);
else if (gain_up && !gain_not_up)
adaptive_increase_gain(gain_up_reason);
}