From 0979750e9eab7a2fc09d789e3d3897721c73a42f Mon Sep 17 00:00:00 2001
From: rtlsdrblog <admin@rtl-sdr.com>
Date: Wed, 23 Aug 2023 23:34:39 +1200
Subject: [PATCH] add auto enable direct sampling when tuned below 28.8 MHz

---
 src/librtlsdr.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/librtlsdr.c b/src/librtlsdr.c
index 227fabb..e84d69c 100644
--- a/src/librtlsdr.c
+++ b/src/librtlsdr.c
@@ -125,6 +125,7 @@ struct rtlsdr_dev {
 
 void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val);
 static int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq);
+static int rtlsdr_update_ds(rtlsdr_dev_t *dev, uint32_t freq);
 
 /* generic tuner interface functions, shall be moved to the tuner implementations */
 int e4000_init(void *dev) {
@@ -888,6 +889,8 @@ int rtlsdr_set_center_freq(rtlsdr_dev_t *dev, uint32_t freq)
 	if (!dev || !dev->tuner)
 		return -1;
 
+	rtlsdr_update_ds(dev, freq);
+
 	if (dev->direct_sampling) {
 		r = rtlsdr_set_if_freq(dev, freq);
 	} else if (dev->tuner && dev->tuner->set_freq) {
@@ -1225,6 +1228,28 @@ int rtlsdr_set_direct_sampling(rtlsdr_dev_t *dev, int on)
 	return r;
 }
 
+static int rtlsdr_update_ds(rtlsdr_dev_t *dev, uint32_t freq)
+{
+	int new_ds;
+	int curr_ds;
+
+        if (!dev)
+                return -1;
+
+	curr_ds = rtlsdr_get_direct_sampling(dev);
+	if (curr_ds < 0)
+		return 1;
+
+	new_ds = freq < 28800000 ? 2 : 0;
+	dev->direct_sampling = new_ds;
+
+	if (curr_ds != new_ds) {
+		return rtlsdr_set_direct_sampling(dev, new_ds);
+	}
+
+	return 0;
+}
+
 int rtlsdr_get_direct_sampling(rtlsdr_dev_t *dev)
 {
 	if (!dev)