From 83c25ee8a283cbb71720677fe21876c0bb43d32a Mon Sep 17 00:00:00 2001
From: Linar Yusupov <linar.r.yusupov@gmail.com>
Date: Mon, 5 Feb 2024 07:11:57 +0300
Subject: [PATCH] SX12xx and CC13x2 radios: align legacy protocol carrier
 frequency setting with Nordic nRF905 100 kHz (LF) or 200 kHz (HF) resolution
 (step)

---
 .../firmware/source/SoftRF/src/driver/RF.cpp  | 20 ++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/software/firmware/source/SoftRF/src/driver/RF.cpp b/software/firmware/source/SoftRF/src/driver/RF.cpp
index 7a55e0b09..e44598683 100644
--- a/software/firmware/source/SoftRF/src/driver/RF.cpp
+++ b/software/firmware/source/SoftRF/src/driver/RF.cpp
@@ -872,6 +872,15 @@ static void sx12xx_channel(int8_t channel)
     uint32_t frequency = RF_FreqPlan.getChanFrequency((uint8_t) channel);
     int8_t fc = settings->freq_corr;
 
+    if (LMIC.protocol->type == RF_PROTOCOL_LEGACY) {
+      nRF905_band_t nrf_band;
+      uint32_t nrf_freq_resolution;
+
+      nrf_band = (frequency >= 844800000UL ? NRF905_BAND_868 : NRF905_BAND_433);
+      nrf_freq_resolution = (nrf_band == NRF905_BAND_433 ? 100000UL : 200000UL);
+      frequency -= (frequency % nrf_freq_resolution);
+    }
+
     //Serial.print("frequency: "); Serial.println(frequency);
 
     if (sx12xx_receive_active) {
@@ -892,7 +901,7 @@ static void sx12xx_channel(int8_t channel)
     }
 
 #if defined(ENABLE_PROL)
-    if (settings->rf_protocol == RF_PROTOCOL_APRS) {
+    if (LMIC.protocol->type == RF_PROTOCOL_APRS) {
       frequency = 433775000UL;
     }
 #endif /* ENABLE_PROL */
@@ -1847,6 +1856,15 @@ static void cc13xx_channel(int8_t channel)
       channel != cc13xx_channel_prev) {
     uint32_t frequency = RF_FreqPlan.getChanFrequency((uint8_t) channel);
 
+    if (settings->rf_protocol == RF_PROTOCOL_LEGACY) {
+      nRF905_band_t nrf_band;
+      uint32_t nrf_freq_resolution;
+
+      nrf_band = (frequency >= 844800000UL ? NRF905_BAND_868 : NRF905_BAND_433);
+      nrf_freq_resolution = (nrf_band == NRF905_BAND_433 ? 100000UL : 200000UL);
+      frequency -= (frequency % nrf_freq_resolution);
+    }
+
     if (cc13xx_receive_active) {
       /* restart Rx upon a channel switch */
       EasyLink_abort();