Use 200 KHz frequency steps for North American FM band plan

Improved the FM band plan description scheme so it can include the
frequency step, and set the North American band plan to use 200 KHz
as the step size to match expected radio behavior.  The Japan band
plan is set to still use 100 KHz, as that seems to be accurate for
the FM band in that locale.

Beyond matching expectations of actual North American car radio
behavior, the user benefit of this change is less button pressing
and exposure to static or dead air in the higher level application.

Change-Id: Ic3474ae8a8e96702efbcf1ea63703c7ea59d2dca
Signed-off-by: Scott Murray <scott.murray@konsulko.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/rtlfmradiotunercontrol.cpp b/rtlfmradiotunercontrol.cpp
index 99054ac..a50b3ef 100644
--- a/rtlfmradiotunercontrol.cpp
+++ b/rtlfmradiotunercontrol.cpp
@@ -15,6 +15,13 @@
 #include <QtCore/QTimer>
 #include <QtCore/QSettings>
 
+// Structure to describe FM band plans, all values in Hz.
+struct fmBandPlan {
+    unsigned int minFreq;
+    unsigned int maxFreq;
+    unsigned int freqStep;
+};
+
 class RtlFmRadioTunerControl::Private
 {
 public:
@@ -39,12 +46,12 @@ public:
     bool searchOne;
     int step;
     bool present;
-    QPair<int, int> fmBandPlan;
+    struct fmBandPlan fmBandPlan;
 
 private:
-    QMap<QString, QPair<int, int> > knownFmBandPlans = {
-      { QString::fromUtf8("US"), qMakePair(87900000, 107900000) },
-      { QString::fromUtf8("JP"), qMakePair(76100000, 89900000) }
+    QMap<QString, struct fmBandPlan> knownFmBandPlans = {
+        { QString::fromUtf8("US"), { .minFreq = 87900000, .maxFreq = 107900000, .freqStep = 200000 } },
+        { QString::fromUtf8("JP"), { .minFreq = 76100000, .maxFreq = 89900000, .freqStep = 100000 } }
     };
 
     static void output_thread_fn(int16_t *result, int result_len, void *ctx);
@@ -102,7 +109,7 @@ RtlFmRadioTunerControl::Private::Private(RtlFmRadioTunerControl *parent)
     fmBandPlan = knownFmBandPlans.value(settings.value("fmbandplan").toString());
 
     // Initialize frequency to lower bound of band plan
-    frequency = fmBandPlan.first;
+    frequency = fmBandPlan.minFreq;
 
     connect(q, &RtlFmRadioTunerControl::stationFound, [this](int frequency, const QString &name) {
         qDebug() << frequency << name;
@@ -193,7 +200,7 @@ int RtlFmRadioTunerControl::frequencyStep(QRadioTuner::Band band) const
         ret = 1000; // 1 kHz
         break;
     case QRadioTuner::FM:
-        ret = 100000; // 0.1 MHz
+        ret = d->fmBandPlan.freqStep;
         break;
     default:
         break;
@@ -210,7 +217,7 @@ QPair<int,int> RtlFmRadioTunerControl::frequencyRange(QRadioTuner::Band band) co
         ret = qMakePair<int,int>(531000, 1602000);
         break;
     case QRadioTuner::FM:
-        ret = QPair<int,int>(d->fmBandPlan);
+        ret = qMakePair<int,int>(d->fmBandPlan.minFreq, d->fmBandPlan.maxFreq);
         break;
     default:
         break;