[lightwaverf] Fix ISR safety issues (#14563)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

esphome/components/lightwaverf/LwRx.cpp

@@ -8,6 +8,7 @@
 
 #include "LwRx.h"
 #include <cstring>
+#include "esphome/core/helpers.h"
 
 namespace esphome {
 namespace lightwaverf {
@@ -185,13 +186,20 @@ bool LwRx::lwrx_getmessage(uint8_t *buf, uint8_t len) {
   bool ret = true;
   int16_t j = 0;  // int
   if (this->rx_msgcomplete && len <= RX_MSGLEN) {
+    // Copy message under interrupt lock to prevent ISR overwriting rx_msg mid-read
+    uint8_t msg_copy[RX_MSGLEN];
+    {
+      InterruptLock lock;
+      memcpy(msg_copy, this->rx_msg, RX_MSGLEN);
+      this->rx_msgcomplete = false;
+    }
     for (uint8_t i = 0; ret && i < RX_MSGLEN; i++) {
       if (this->rx_translate || (len != RX_MSGLEN)) {
-        j = this->rx_find_nibble_(this->rx_msg[i]);
+        j = this->rx_find_nibble_(msg_copy[i]);
         if (j < 0)
           ret = false;
       } else {
-        j = this->rx_msg[i];
+        j = msg_copy[i];
       }
       switch (len) {
         case 4:
@@ -199,6 +207,7 @@ bool LwRx::lwrx_getmessage(uint8_t *buf, uint8_t len) {
             buf[2] = j;
           if (i == 2)
             buf[3] = j;
+          [[fallthrough]];
         case 2:
           if (i == 3)
             buf[0] = j;
@@ -212,7 +221,6 @@ bool LwRx::lwrx_getmessage(uint8_t *buf, uint8_t len) {
           break;
       }
     }
-    this->rx_msgcomplete = false;
   } else {
     ret = false;
   }

esphome/components/lightwaverf/LwRx.h

@@ -105,8 +105,8 @@ class LwRx {
 
   uint32_t rx_prev;  // time of previous interrupt in microseconds
 
-  bool rx_msgcomplete = false;  // set high when message available
-  bool rx_translate = true;     // Set false to get raw data
+  volatile bool rx_msgcomplete = false;  // set high when message available
+  bool rx_translate = true;              // Set false to get raw data
 
   uint8_t rx_state = 0;
 

esphome/components/lightwaverf/LwTx.cpp

@@ -192,7 +192,8 @@ void LwTx::lwtx_set_gap_multiplier(uint8_t gap_multiplier) { this->tx_gap_multip
 void LwTx::lw_timer_start() {
   {
     InterruptLock lock;
-    static LwTx *arg = this;  // NOLINT
+    static LwTx *arg;
+    arg = this;
     timer1_attachInterrupt([] { isr_t_xtimer(arg); });
     timer1_enable(TIM_DIV16, TIM_EDGE, TIM_LOOP);
     timer1_write(this->espPeriod);

esphome/components/lightwaverf/LwTx.h

@@ -62,8 +62,8 @@ class LwTx {
   uint8_t tx_repeats = 12;  // Number of repeats of message sent
   uint8_t txon = 1;
   uint8_t txoff = 0;
-  bool tx_msg_active = false;  // set true to activate message sending
-  bool tx_translate = true;    // Set false to send raw data
+  volatile bool tx_msg_active = false;  // set true to activate message sending
+  bool tx_translate = true;             // Set false to send raw data
 
   uint8_t tx_buf[TX_MSGLEN];  // the message buffer during reception
   uint8_t tx_repeat = 0;      // counter for repeats