Fix ESC spinup during settings save using circular DMA

src/main/config/config_eeprom.c

@@ -33,6 +33,7 @@
 
 #include "drivers/system.h"
 #include "drivers/flash.h"
+#include "drivers/pwm_output.h"
 
 #include "fc/config.h"
 
@@ -321,6 +322,16 @@ static bool writeSettingsToEEPROM(void)
 
 void writeConfigToEEPROM(void)
 {
+    // Prevent ESC spinup during settings save using circular DMA
+    pwmSetMotorDMACircular(true);
+
+    // Force motor updates to latch current (zero) throttle into circular DMA buffer
+    pwmCompleteMotorUpdate();
+    delayMicroseconds(200);
+    pwmCompleteMotorUpdate();
+    delayMicroseconds(200);
+    pwmCompleteMotorUpdate();
+
     bool success = false;
     // write it
     for (int attempt = 0; attempt < 3 && !success; attempt++) {
@@ -333,6 +344,9 @@ void writeConfigToEEPROM(void)
         }
     }
 
+    // Restore normal DMA mode
+    pwmSetMotorDMACircular(false);
+
     if (success && isEEPROMContentValid()) {
         return;
     }

src/main/drivers/pwm_output.c

@@ -226,6 +226,20 @@ void pwmEnableMotors(void)
     pwmMotorsEnabled = true;
 }
 
+void pwmSetMotorDMACircular(bool circular)
+{
+#ifdef USE_DSHOT
+    // Set DMA circular mode for all motor outputs
+    for (int i = 0; i < getMotorCount(); i++) {
+        if (motors[i].pwmPort && motors[i].pwmPort->tch) {
+            impl_timerPWMSetDMACircular(motors[i].pwmPort->tch, circular);
+        }
+    }
+#else
+    UNUSED(circular);
+#endif
+}
+
 bool isMotorBrushed(uint16_t motorPwmRateHz)
 {
     return (motorPwmRateHz > 500);

src/main/drivers/pwm_output.h

@@ -50,6 +50,7 @@ void pwmWriteServo(uint8_t index, uint16_t value);
 
 void pwmDisableMotors(void);
 void pwmEnableMotors(void);
+void pwmSetMotorDMACircular(bool circular);
 struct timerHardware_s;
 
 void pwmMotorPreconfigure(void);

src/main/drivers/timer_impl.h

@@ -84,6 +84,7 @@ bool impl_timerPWMConfigChannelDMA(TCH_t * tch, void * dmaBuffer, uint8_t dmaBuf
 void impl_timerPWMPrepareDMA(TCH_t * tch, uint32_t dmaBufferElementCount);
 void impl_timerPWMStartDMA(TCH_t * tch);
 void impl_timerPWMStopDMA(TCH_t * tch);
+void impl_timerPWMSetDMACircular(TCH_t * tch, bool circular);
 
 #ifdef USE_DSHOT_DMAR
 bool impl_timerPWMConfigDMABurst(burstDmaTimer_t *burstDmaTimer, TCH_t * tch, void * dmaBuffer, uint8_t dmaBufferElementSize, uint32_t dmaBufferElementCount);

src/main/drivers/timer_impl_hal.c

@@ -580,3 +580,54 @@ void impl_timerPWMStopDMA(TCH_t * tch)
 
     HAL_TIM_Base_Start(tch->timCtx->timHandle);
 }
+
+void impl_timerPWMSetDMACircular(TCH_t * tch, bool circular)
+{
+    if (!tch->dma || !tch->dma->dma) {
+        return;
+    }
+
+    const uint32_t streamLL = lookupDMALLStreamTable[DMATAG_GET_STREAM(tch->timHw->dmaTag)];
+    DMA_TypeDef *dmaBase = tch->dma->dma;
+
+    // Save the current transfer count before disabling
+    uint32_t dataLength = LL_DMA_GetDataLength(dmaBase, streamLL);
+
+    // Protect DMA reconfiguration from interrupt interference
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        // Disable timer DMA request first to stop new transfer triggers
+        LL_TIM_DisableDMAReq_CCx(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex]);
+
+        // Disable the DMA stream
+        LL_DMA_DisableStream(dmaBase, streamLL);
+
+        // CRITICAL: Wait for stream to actually become disabled
+        // The EN bit doesn't clear immediately, especially if transfer is in progress
+        uint32_t timeout = 10000;
+        while (LL_DMA_IsEnabledStream(dmaBase, streamLL) && timeout--) {
+            __NOP();
+        }
+
+        // Clear any pending transfer complete flags
+        DMA_CLEAR_FLAG(tch->dma, DMA_IT_TCIF);
+
+        // Modify the DMA mode
+        if (circular) {
+            LL_DMA_SetMode(dmaBase, streamLL, LL_DMA_MODE_CIRCULAR);
+        } else {
+            LL_DMA_SetMode(dmaBase, streamLL, LL_DMA_MODE_NORMAL);
+        }
+
+        // Reload the transfer count (required after mode change)
+        // If dataLength was 0 (transfer completed), keep it at 0 - the next motor update will reload it
+        if (dataLength > 0) {
+            LL_DMA_SetDataLength(dmaBase, streamLL, dataLength);
+        }
+
+        // Re-enable DMA stream
+        LL_DMA_EnableStream(dmaBase, streamLL);
+
+        // Re-enable timer DMA requests
+        LL_TIM_EnableDMAReq_CCx(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex]);
+    }
+}

src/main/drivers/timer_impl_stdperiph.c

@@ -519,3 +519,26 @@ void impl_timerPWMStopDMA(TCH_t * tch)
     tch->dmaState = TCH_DMA_IDLE;
     TIM_Cmd(tch->timHw->tim, ENABLE);
 }
+
+void impl_timerPWMSetDMACircular(TCH_t * tch, bool circular)
+{
+    if (!tch->dma || !tch->dma->ref) {
+        return;
+    }
+
+    // Protect DMA reconfiguration from interrupt interference
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        // Temporarily disable DMA while modifying configuration
+        DMA_Cmd(tch->dma->ref, DISABLE);
+
+        // Modify the DMA mode
+        if (circular) {
+            tch->dma->ref->CR |= DMA_SxCR_CIRC;  // Set circular bit
+        } else {
+            tch->dma->ref->CR &= ~DMA_SxCR_CIRC; // Clear circular bit
+        }
+
+        // Re-enable DMA
+        DMA_Cmd(tch->dma->ref, ENABLE);
+    }
+}

src/main/drivers/timer_impl_stdperiph_at32.c

@@ -407,3 +407,26 @@ void impl_timerPWMStopDMA(TCH_t * tch)
     tch->dmaState = TCH_DMA_IDLE;
     tmr_counter_enable(tch->timHw->tim, TRUE);
 }
+
+void impl_timerPWMSetDMACircular(TCH_t * tch, bool circular)
+{
+    if (!tch->dma || !tch->dma->ref) {
+        return;
+    }
+
+    // Protect DMA reconfiguration from interrupt interference
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        // Temporarily disable DMA while modifying configuration
+        dma_channel_enable(tch->dma->ref, FALSE);
+
+        // Modify the DMA loop mode (AT32's equivalent of circular mode)
+        if (circular) {
+            tch->dma->ref->ctrl_bit.lm = TRUE;  // Enable loop mode
+        } else {
+            tch->dma->ref->ctrl_bit.lm = FALSE; // Disable loop mode
+        }
+
+        // Re-enable DMA
+        dma_channel_enable(tch->dma->ref, TRUE);
+    }
+}

src/main/fc/config.c

@@ -420,7 +420,7 @@ void processDelayedSave(void)
         saveState = SAVESTATE_NONE;
     } else if (saveState == SAVESTATE_SAVEONLY) {
         suspendRxSignal();
-        writeEEPROM();
+        writeEEPROM();  // Circular DMA protection is inside writeConfigToEEPROM()
         resumeRxSignal();
         saveState = SAVESTATE_NONE;
     }