From fe5cdc06dd2bfbd81d1f2e92a822fe0a1446fe9d Mon Sep 17 00:00:00 2001
From: 0xSeren <0xseren@tutamail.com>
Date: Thu, 16 Apr 2026 17:39:58 -0400
Subject: [PATCH] fix: enable LoRa CRC on SX127x for RNode interop

After reset, SX127x hardware leaves REG_MODEM_CONFIG_2 bit 2
(RxPayloadCrcOn) cleared, and RadioLib's SX127x::begin() does not
touch it. Upstream RNode firmware explicitly enables CRC on every
LoRa transmit and receive path (sx127x::enableCrc in
RNode_Firmware.ino:531, sx127x.cpp:160), so a real RNode will
silently drop frames that arrive without a valid CRC.

This means T-Beam and LoRa32 V2.1 users running the example
LoRaInterface cannot interop with real RNodes over LoRa today:
outbound packets are dropped at the RNode, inbound packets may be
accepted but silently corrupted.

Fix by calling chip->setCRC(true) after SX1276::begin() in the
SX127x branch of LoRaInterface::start(). The new call is gated on
the prior begin() having succeeded, and its own error is folded
into state so the existing RADIOLIB_ERR_NONE check catches it.

No change required on the SX126x branches: RadioLib's
SX126x::begin() already calls setCRC(2), so RAK4631, Heltec V3,
and Heltec V4 inherit CRC-on.
---
 examples/common/lora_interface/LoRaInterface.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/examples/common/lora_interface/LoRaInterface.cpp b/examples/common/lora_interface/LoRaInterface.cpp
index 9cf0279..9d01265 100644
--- a/examples/common/lora_interface/LoRaInterface.cpp
+++ b/examples/common/lora_interface/LoRaInterface.cpp
@@ -109,6 +109,13 @@ bool LoRaInterface::start() {
 	// begin(freq MHz, bw kHz, sf, cr, syncWord, power dBm, preamble symbols, LNA gain 0=AGC)
 	int state = chip->begin(frequency, bandwidth, spreading, coding,
 	                        RADIOLIB_SX127X_SYNC_WORD, power, 20, 0);
+	// SX127x hardware default leaves RxPayloadCrcOn=0 and RadioLib's
+	// SX127x::begin() does not touch it. Upstream RNode firmware enables
+	// CRC unconditionally (sx127x::enableCrc, RNode_Firmware.ino:531), so
+	// real RNodes silently drop frames without a CRC. Enable it here to
+	// interoperate. SX126x branches below inherit CRC-on from
+	// SX126x::begin() (setCRC(2)), so no explicit call is needed there.
+	if (state == RADIOLIB_ERR_NONE) state = chip->setCRC(true);
 
 #elif defined(BOARD_RAK4631)
 	// nRF52: SPI pins must be configured before SPI.begin()