Split rtlsdr code into standalone helper

To avoid the GPL licensed code in rtl_fm.c making all of the binding
GPL, rework things to wrap it with a simple standalone helper
executable that is driven via stdin/stdout.  While this could
potentially be done by running the original unmodified rtl_fm utility
itself, it would be impossible to implement scanning with that
approach without some compromising of playback latency and quality.
The current helper implementation is simple enough that replacing it
with an alternate one should be relatively straightforward if that is
desired.

Change-Id: If83b834da3999f5807d1453524ae72b1c3559c90
Signed-off-by: Scott Murray <scottm@ghidorah.spiteful.org>

1 files changed, 242 insertions, 0 deletions

diff --git a/binding/rtl_fm_helper.c b/binding/rtl_fm_helper.c
new file mode 100644
index 0000000..9405ae2
--- /dev/null
+++ b/binding/rtl_fm_helper.c
@@ -0,0 +1,242 @@
+/*
+ * Copyright (C) 2018 Konsulko Group
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <glib.h>
+
+#include "rtl_fm.h"
+#include "radio_output.h"
+
+#ifdef DEBUG
+#define LOG_FILE	"/tmp/helper.log"
+FILE *_log;
+#define LOG(...) \
+	do { \
+		if(!_log) _log = fopen(LOG_FILE, "w");	\
+		fprintf(_log, __VA_ARGS__);		\
+		fflush(_log);				\
+	} while(0)
+#else
+#define LOG(...) do { } while(0)
+#endif
+
+// Structure to describe FM band plans, all values in Hz.
+typedef struct {
+	const char *name;
+	uint32_t min;
+	uint32_t max;
+	uint32_t step;
+} fm_band_plan_t;
+
+static fm_band_plan_t known_fm_band_plans[5] = {
+	{ .name = "US", .min = 87900000, .max = 107900000, .step = 200000 },
+	{ .name = "JP", .min = 76000000, .max = 95000000, .step = 100000 },
+	{ .name = "EU", .min = 87500000, .max = 108000000, .step = 50000 },
+	{ .name = "ITU-1", .min = 87500000, .max = 108000000, .step = 50000 },
+	{ .name = "ITU-2", .min = 87900000, .max = 107900000, .step = 50000 }
+};
+
+static unsigned int bandplan;
+static char line[64];
+
+static void rtl_output_callback(int16_t *result, int result_len, void *ctx)
+{
+	radio_output_write((char*) result, result_len * 2);
+}
+
+static void rtl_freq_callback(uint32_t freq, void *ctx)
+{
+	// Note, need to flush output to ensure parent sees it
+	printf("F=%u\n", freq);
+	fflush(stdout);
+	LOG("F=%u\n", freq);
+}
+
+static void rtl_scan_callback(uint32_t freq, void *ctx)
+{
+	// Note, need to flush output to ensure parent sees it
+	printf("S=%u\n", freq);
+	fflush(stdout);
+	LOG("S=%u\n", freq);
+}
+
+static void read_config(void)
+{
+	GKeyFile* conf_file;
+	int conf_file_present = 0;
+	char *value_str;
+
+	// Load settings from configuration file if it exists
+	conf_file = g_key_file_new();
+	if(conf_file &&
+	   g_key_file_load_from_dirs(conf_file,
+				     "AGL.conf",
+				     (const gchar**) g_get_system_config_dirs(),
+				     NULL,
+				     G_KEY_FILE_KEEP_COMMENTS,
+				     NULL) == TRUE) {
+		conf_file_present = 1;
+
+		// Set band plan if it is specified
+		value_str = g_key_file_get_string(conf_file,
+						  "radio",
+						  "fmbandplan",
+						  NULL);
+		if(value_str) {
+			unsigned int i;
+			for(i = 0;
+			    i < sizeof(known_fm_band_plans) / sizeof(fm_band_plan_t);
+			    i++) {
+				if(!strcasecmp(value_str, known_fm_band_plans[i].name)) {
+					bandplan = i;
+					break;
+				}
+			}
+		}
+	}
+	fprintf(stderr, "Using FM Bandplan: %s\n", known_fm_band_plans[bandplan].name);
+
+	if(conf_file_present) {
+		GError *error = NULL;
+		int n;
+
+		// Allow over-riding scanning parameters just in case a demo
+		// setup needs to do so to work reliably.
+		n = g_key_file_get_integer(conf_file,
+					   "radio",
+					   "scan_squelch_level",
+					   &error);
+		if(!error) {
+			fprintf(stderr, "Scanning squelch level set to %d\n", n);
+			rtl_fm_scan_set_squelch_level(n);
+		}
+
+		error = NULL;
+		n = g_key_file_get_integer(conf_file,
+					   "radio",
+					   "scan_squelch_limit",
+					   &error);
+		if(!error) {
+			fprintf(stderr, "Scanning squelch limit set to %d\n", n);
+			rtl_fm_scan_set_squelch_limit(n);
+		}
+
+		g_key_file_free(conf_file);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	int rc;
+	bool detect = false;
+	bool done = false;
+	bool started = false;
+	uint32_t frequency;
+
+	LOG("started\n");
+
+	read_config();
+	frequency = known_fm_band_plans[bandplan].min;
+
+	if(argc == 2 && strcmp(argv[1], "--detect") == 0) {
+		detect = true;
+	}
+
+	rc = rtl_fm_init(frequency, 200000, 48000, rtl_output_callback, NULL);
+	if(rc < 0) {
+		fprintf(stderr, "No RTL USB adapter?\n");
+		exit(1);
+	}
+	if(detect) {
+		rtl_fm_cleanup();
+		exit(0);
+	}
+
+	rtl_fm_set_freq_callback(rtl_freq_callback, NULL);
+
+	while(!done) {
+		LOG("Reading command\n");
+		fgets(line, sizeof(line), stdin);
+		if(line[0] == '\0' || line[0] == '\n')
+			continue;
+		if(strcmp(line, "START\n") == 0) {
+			LOG("START received\n");
+			if(!started) {
+				LOG("Starting\n");
+				radio_output_start();
+				rtl_fm_start();
+				started = true;
+			}
+		} else if(strcmp(line, "STOP\n") == 0) {
+			LOG("STOP received\n");
+			if(started) {
+				LOG("Stopping\n");
+				radio_output_stop();
+				rtl_fm_stop();
+				started = false;
+			}
+		} else if(strncmp(line, "F=", 2) == 0) {
+			uint32_t n;
+			if(sscanf(line, "F=%u\n", &n) == 1) {
+				LOG("F=%d received\n", n);
+				rtl_fm_scan_stop();
+				rtl_fm_set_freq(n);
+			}
+		} else if(strcmp(line, "S=UP\n") == 0) {
+			LOG("S=UP received\n");
+			if(!started)
+				continue;
+			LOG("Calling rtl_fm_scan_start\n");
+			rtl_fm_scan_start(0,
+					  rtl_scan_callback,
+					  NULL,
+					  known_fm_band_plans[bandplan].step,
+					  known_fm_band_plans[bandplan].min,
+					  known_fm_band_plans[bandplan].max);
+		} else if(strcmp(line, "S=DOWN\n") == 0) {
+			LOG("S=DOWN received\n");
+			if(!started)
+				continue;
+			LOG("Calling rtl_fm_scan_start\n");
+			rtl_fm_scan_start(1,
+					  rtl_scan_callback,
+					  NULL,
+					  known_fm_band_plans[bandplan].step,
+					  known_fm_band_plans[bandplan].min,
+					  known_fm_band_plans[bandplan].max);
+		} else if(strcmp(line, "S=STOP\n") == 0) {
+			LOG("S=STOP received\n");
+			if(started) {
+				LOG("Calling rtl_fm_scan_stop\n");
+				rtl_fm_scan_stop();
+			}
+		} else if(line[0] == 'q' || line[0] == 'Q')
+			break;
+	}
+	if(started) {
+		radio_output_stop();
+		rtl_fm_stop();
+	}
+	rtl_fm_cleanup();
+	LOG("done");
+	return 0;
+}