added passthrough driver option 'inc=' for impulse noise cancellation

* passthrough from environment variable 'LIBRTLSDR_OPT'
* should/could be beneficial for ads-b

Signed-off-by: hayati ayguen <h_ayguen@web.de>

README_improvements.md

@@ -68,24 +68,18 @@ against librtlsdr's development branch (initially same date, but updated 2020-10
     * **tp=** set pin for bias tee
     * **ds=** set direct sampling (HF mode) for RTL-SDR V3 or compatible, see https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/
     * **dm=** set direct sampling mode
+    * **inc=** set impulse noise cancellation (default is on), might be useful to deactivate for ADS-B
 
   * many of the options are R820T/2-tuner specific:
 
     * **bc=** set the the reception bands' center in Hz
-
     * **sb=** set tuner sideband
-
     * **ifm=** set IF mode (AGC, fixed gain, ..) for VGA (variable gain amplifier)
-
     * **harm=** set n-th harmonic reception
-
     * **vcocmin=** set minimum VCO current
-
     * **vcocmax=** set maximum VCO current
-
     * **vcoalgo=** set VCO algorithm
 
-      
 
 * probably some more: it's highly probable, that this list is incomplete
 
@@ -114,6 +108,8 @@ new alternative: environment variable **LIBRTLSDR_OPT**
 * added rtlsdr_set_center_freq64(), to set frequencies above ~4.29 GHz, the 32-bit limit
 * added rtlsdr_get_center_freq64()
 * added rtlsdr_set_harmonic_rx() to activate/change harmonic reception
+* added rtlsdr_set_impulse_nc(), rtlsdr_get_impulse_nc()
+* added rtlsdr_set_aagc(), rtlsdr_set_aagc_gain_distrib() and getters
 
 
 ## Added Tools

src/librtlsdr.c

@@ -4670,6 +4670,7 @@ const char * rtlsdr_get_opt_help(int longInfo)
 		"\t\t                        default port number: 32323\n"
 #endif
 		"\t\tstandby=<on>          1 activates standby after close, 0 deactivates to keep heated-up\n"
+		"\t\tinc=<on>              1 activates the impulse noise cancellation (=default), 0 deactivates it\n"
 		;
 	else
 		return
@@ -4685,7 +4686,7 @@ const char * rtlsdr_get_opt_help(int longInfo)
 #else
 		"\t\tds=<direct_sampling>:dm=<ds_mode_thresh>:T=<bias_tee>"
 #endif
-		":standby=<en>\n"
+		":standby=<en>:inc=<en>\n"
 #ifdef WITH_UDP_SERVER
 		"\t\tport=<udp_port default with 1>\n"
 #endif
@@ -4913,6 +4914,12 @@ int rtlsdr_set_opt_string(rtlsdr_dev_t *dev, const char *opts, int verbose)
 				fprintf(stderr, "\nrtlsdr_set_opt_string(): parsed standby %d\n", on);
 			ret = rtlsdr_standby_after_close(dev, on);
 		}
+		else if (!strncmp(optPart, "inc=", 4)) {
+			int on = atoi(optPart +4);
+			if (verbose)
+				fprintf(stderr, "\nrtlsdr_set_opt_string(): parsed impulse noise cancellation %d\n", on);
+			ret = rtlsdr_set_impulse_nc(dev, on, 1);
+		}
 		else if (*optPart) {
 			if (verbose)
 				fprintf(stderr, "\nrtlsdr_set_opt_string(): parsed unknown option '%s'\n", optPart);