ExpressLRS - Fix data-race in ISR handling that was observed that caused

RX loss. Likely caused by RX task running *very* late and a new EXTI flag being set, and then being immediately cleared without processing it. More likely to happen on the bench than in the air due to task latency caused by USB activity.
betaflight · Jan 28, 2022 · a91166b · a91166b
1 parent 3c5a572
commit a91166b
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Showing 2 changed files with 36 additions and 15 deletions.
diff --git a/src/main/drivers/rx/rx_sx127x.c b/src/main/drivers/rx/rx_sx127x.c
@@ -31,9 +31,12 @@
 
 #ifdef USE_RX_SX127X
 
+#include "build/atomic.h"
+
 #include "drivers/bus_spi.h"
 #include "drivers/io.h"
 #include "drivers/io_impl.h"
+#include "drivers/nvic.h"
 #include "drivers/rx/rx_sx127x.h"
 #include "drivers/rx/rx_spi.h"
 #include "drivers/time.h"
@@ -73,15 +76,23 @@ static bool sx127xDetectChip(void)
 
 uint8_t sx127xISR(timeUs_t *timeStamp)
 {
-    if (rxSpiPollExti()) {
-        if (rxSpiGetLastExtiTimeUs()) {
-            *timeStamp = rxSpiGetLastExtiTimeUs();
-        }
+    bool extiTriggered = false;
+    timeUs_t extiTimestamp;
 
-        uint8_t irqReason;
-        irqReason = sx127xGetIrqReason();
+    ATOMIC_BLOCK(NVIC_PRIO_RX_SPI_INT_EXTI) {
+        // prevent a data-race that can occur if a new EXTI ISR occurs during this block.
+        extiTriggered = rxSpiPollExti();
+        extiTimestamp = rxSpiGetLastExtiTimeUs();
+        if (extiTriggered) {
+            rxSpiResetExti();
+        }
+    }
 
-        rxSpiResetExti();
+    if (extiTriggered) {
+        uint8_t irqReason = sx127xGetIrqReason();
+        if (extiTimestamp) {
+            *timeStamp = extiTimestamp;
+        }
 
         return irqReason;
     }

diff --git a/src/main/drivers/rx/rx_sx1280.c b/src/main/drivers/rx/rx_sx1280.c
@@ -32,9 +32,12 @@
 
 #ifdef USE_RX_SX1280
 
+#include "build/atomic.h"
+
 #include "drivers/bus_spi.h"
 #include "drivers/io.h"
 #include "drivers/io_impl.h"
+#include "drivers/nvic.h"
 #include "drivers/rx/rx_sx1280.h"
 #include "drivers/rx/rx_spi.h"
 #include "drivers/time.h"
@@ -103,16 +106,23 @@ bool sx1280Init(IO_t resetPin, IO_t busyPin)
 
 uint8_t sx1280ISR(timeUs_t *timeStamp)
 {
-    if (rxSpiPollExti()) {
-        if (rxSpiGetLastExtiTimeUs()) {
-            *timeStamp = rxSpiGetLastExtiTimeUs();
-        }
-
-        uint8_t irqReason;
-        irqReason = sx1280GetIrqReason();
+    bool extiTriggered = false;
+    timeUs_t extiTimestamp;
 
-        rxSpiResetExti();
+    ATOMIC_BLOCK(NVIC_PRIO_RX_SPI_INT_EXTI) {
+        // prevent a data-race that can occur if a new EXTI ISR occurs during this block.
+        extiTriggered = rxSpiPollExti();
+        extiTimestamp = rxSpiGetLastExtiTimeUs();
+        if (extiTriggered) {
+            rxSpiResetExti();
+        }
+    }
 
+    if (extiTriggered) {
+        uint8_t irqReason = sx1280GetIrqReason();
+        if (extiTimestamp) {
+            *timeStamp = extiTimestamp;
+        }
         return irqReason;
     }
     return 0;