Refactor unsigned sample reading into read_samples_cu8()

Instead of having rtl_fm and rtl_sdr convert CS8 to CU8, add the
read_samples_cu8() convenience function. This reads from SoapySDR using
CS8 format, and adds 127 to convert to CU8, the actual native format - a
redundant but necessary conversion, could be improved after
pothosware/SoapyRTLSDR#15 if SoapyRTLSDR adds
native CU8 support (remove the loop in read_samples_cu8()).

src/convenience/convenience.c

@@ -389,4 +389,32 @@ int verbose_device_search(char *s)
 	return -1;
 }
 
+int read_samples_cu8(SoapySDRDevice *dev, SoapySDRStream *stream, uint8_t *buf, int len)
+{
+	void *buffs[] = {buf};
+	int flags = 0;
+	long long timeNs;
+	long timeoutNs = 100000;
+	int bytes_read, r;
+
+	r = SoapySDRDevice_readStream(dev, stream, buffs, len, &flags, &timeNs, timeoutNs);
+
+	//fprintf(stderr, "readStream ret=%d, flags=%d, timeNs=%lld\n", r, flags, timeNs);
+	if (r >= 0) {
+		// r is number of elements read, elements=complex pairs of 8-bits, so buffer length in bytes is twice
+		bytes_read = r * 2;
+
+		// Convert CS8 to CU8, back to RTL-SDR native format!
+		// TODO: see https://github.com/pothosware/SoapyRTLSDR/issues/15
+		// TODO: or use "direct buffer access API"?
+		// TODO: or2, remove +127 here and -127 in rtlsdr_callback! back and forth too many times (-127 in SoapyRTLSDR)
+		for(int i = 0; i < bytes_read; ++i) {
+			buf[i] += 127;
+		}
+	}
+
+	return bytes_read;
+}
+
+
 // vim: tabstop=8:softtabstop=8:shiftwidth=8:noexpandtab

src/convenience/convenience.h

@@ -154,4 +154,15 @@ int verbose_reset_buffer(SoapySDRDevice *dev);
 
 int verbose_device_search(char *s);
 
+/*!
+ * Read samples as Complex Unsigned 8-bit (CU8) pairs
+ *
+ * \param dev the device handle
+ * \param stream the stream handle
+ * \param buf buffer to read into
+ * \param len maximum length of buffer
+ * \return number of bytes read, or negative if an error
+ */
+int read_samples_cu8(SoapySDRDevice *dev, SoapySDRStream *stream, uint8_t *buf, int len);
+
 #endif /*__CONVENIENCE_H*/

src/rtl_fm.c

@@ -912,26 +912,12 @@ static void *dongle_thread_fn(void *arg)
 	int r = 0;
 	do
 	{
-		void *buffs[] = {buf};
-		int flags = 0;
-		long long timeNs;
-		long timeoutNs = 100000;
-		r = SoapySDRDevice_readStream(s->dev, s->stream, buffs, MAXIMUM_BUF_LENGTH, &flags, &timeNs, timeoutNs);
-		//fprintf(stderr, "ret=%d, flags=%d, timeNs=%lld\n", r, flags, timeNs);
+		r = read_samples_cu8(s->dev, s->stream, buf, MAXIMUM_BUF_LENGTH);
+
 		if (r >= 0) {
-			// r is number of elements read, elements=complex pairs of 8-bits, so buffer length in bytes is twice
-			s->buf_len = r * 2;
-			for(int i = 0; i < s->buf_len; ++i) {
-				//fprintf(stderr, "%.4x ", s->buf16[i]);
-				// Convert CS8 to CU8, back to RTL-SDR native format!
-				// TODO: see https://github.com/pothosware/SoapyRTLSDR/issues/15
-				// TODO: or use "direct buffer access API"?
-                                // TODO: or2, remove +127 here and -127 in rtlsdr_callback! back and forth too many times (-127 in SoapyRTLSDR)
-				buf[i] += 127;
-			}
-			//fprintf(stderr, "\n");
+			s->buf_len = r;
+			rtlsdr_callback(buf, s->buf_len, s);
 		}
-		rtlsdr_callback(buf, s->buf_len, s);
 	} while(r > 0);
 
 	//rtlsdr_read_async(s->dev, rtlsdr_callback, s, 0, s->buf_len);

src/rtl_sdr.c

@@ -227,22 +227,12 @@ int main(int argc, char **argv)
                         exit(1);
                 }
 		while (!do_exit) {
-			void *buffs[] = {buffer};
-			int flags = 0;
-			long long timeNs = 0;
-			r = SoapySDRDevice_readStream(dev, stream, buffs, out_block_size, &flags, &timeNs, 100000);
+			r = read_samples_cu8(dev, stream, buffer, out_block_size);
 			if (r < 0) {
 				fprintf(stderr, "WARNING: sync read failed.\n");
 				break;
-			} else {
-                                // TODO: get native CU8, see https://github.com/pothosware/SoapyRTLSDR/issues/15 also in fm
-				for(int i = 0; i < r; ++i) {
-					buffer[i] += 127;
-				}
 			}
 			n_read = r;
-                        // TODO: convert CS8 to CU8 (+127)
-                        fprintf(stderr, "n_read=%d\n", n_read);
 
 			if ((bytes_to_read > 0) && (bytes_to_read < (uint32_t)n_read)) {
 				n_read = bytes_to_read;
@@ -254,7 +244,7 @@ int main(int argc, char **argv)
 				break;
 			}
 
-                        // TODO: hmm.. n_read 8192, but out_block_size (16 * 16384) is much larger
+                        // TODO: hmm.. n_read 8192, but out_block_size (16 * 16384) is much larger TODO: loop? or accept 8192? rtl_fm ok with it
                         /*
 			if ((uint32_t)n_read < out_block_size) {
 				fprintf(stderr, "Short read, samples lost, exiting! (%d < %d)\n", n_read, out_block_size);