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 +322,13 @@ static bool writeSettingsToEEPROM(void)
 
 void writeConfigToEEPROM(void)
 {
+#if !defined(SITL_BUILD) && defined(USE_DSHOT)
+    // Enable circular DMA so hardware keeps repeating zero-throttle DShot
+    // packets during flash writes (which block the CPU for 20-200ms).
+    // Without this, ESCs lose signal and may spin up or reboot.
+    pwmSetMotorDMACircular(true);
+#endif
+
     bool success = false;
     // write it
     for (int attempt = 0; attempt < 3 && !success; attempt++) {
@@ -333,6 +341,10 @@ void writeConfigToEEPROM(void)
         }
     }
 
+#if !defined(SITL_BUILD) && defined(USE_DSHOT)
+    pwmSetMotorDMACircular(false);
+#endif
+
     if (success && isEEPROMContentValid()) {
         return;
     }

src/main/drivers/pwm_output.c

@@ -124,6 +124,18 @@ static timeUs_t commandPostDelay = 0;
 static circularBuffer_t commandsCircularBuffer;
 static uint8_t commandsBuff[DHSOT_COMMAND_QUEUE_SIZE];
 static currentExecutingCommand_t currentExecutingCommand;
+
+static uint16_t prepareDshotPacket(const uint16_t value, bool requestTelemetry);
+#ifndef USE_DSHOT_DMAR
+static void loadDmaBufferDshot(timerDMASafeType_t *dmaBuffer, uint16_t packet);
+#else
+static void loadDmaBufferDshotStride(timerDMASafeType_t *dmaBuffer, int stride, uint16_t packet);
+#endif
+
+#ifdef USE_DSHOT_DMAR
+burstDmaTimer_t burstDmaTimers[MAX_DMA_TIMERS];
+uint8_t burstDmaTimersCount = 0;
+#endif
 #endif
 
 static void pwmOutConfigTimer(pwmOutputPort_t * p, TCH_t * tch, uint32_t hz, uint16_t period, uint16_t value)
@@ -226,6 +238,56 @@ void pwmEnableMotors(void)
     pwmMotorsEnabled = true;
 }
 
+void pwmSetMotorDMACircular(bool circular)
+{
+#ifdef USE_DSHOT
+    if (!isMotorProtocolDshot()) {
+        return;
+    }
+
+    int motorCount = getMotorCount();
+
+    if (circular) {
+        // Load zero-throttle packets directly into DMA buffers,
+        // bypassing the rate limiter in pwmCompleteMotorUpdate()
+        uint16_t packet = prepareDshotPacket(0, false);
+        for (int i = 0; i < motorCount; i++) {
+            if (motors[i].pwmPort && motors[i].pwmPort->configured) {
+#ifdef USE_DSHOT_DMAR
+                loadDmaBufferDshotStride(&motors[i].pwmPort->dmaBurstBuffer[motors[i].pwmPort->tch->timHw->channelIndex], 4, packet);
+#else
+                loadDmaBufferDshot(motors[i].pwmPort->dmaBuffer, packet);
+#endif
+            }
+        }
+    }
+
+#ifdef USE_DSHOT_DMAR
+    // Burst DMA: one DMA stream per timer, shared across channels
+    for (int i = 0; i < burstDmaTimersCount; i++) {
+        burstDmaTimer_t *burstDmaTimer = &burstDmaTimers[i];
+        // Find the first motor using this timer to get the TCH for DMA state
+        for (int m = 0; m < motorCount; m++) {
+            if (motors[m].pwmPort && motors[m].pwmPort->configured && motors[m].pwmPort->tch
+                && motors[m].pwmPort->tch->timHw->tim == burstDmaTimer->timer) {
+                impl_pwmBurstDMASetCircular(burstDmaTimer, motors[m].pwmPort->tch, circular, DSHOT_DMA_BUFFER_SIZE * 4);
+                break;
+            }
+        }
+    }
+#else
+    // Per-channel DMA: one DMA stream per motor
+    for (int i = 0; i < motorCount; i++) {
+        if (motors[i].pwmPort && motors[i].pwmPort->configured && motors[i].pwmPort->tch) {
+            impl_timerPWMSetDMACircular(motors[i].pwmPort->tch, circular, DSHOT_DMA_BUFFER_SIZE);
+        }
+    }
+#endif
+#else
+    UNUSED(circular);
+#endif
+}
+
 bool isMotorBrushed(uint16_t motorPwmRateHz)
 {
     return (motorPwmRateHz > 500);
@@ -264,9 +326,6 @@ uint32_t getDshotHz(motorPwmProtocolTypes_e pwmProtocolType)
 }
 
 #ifdef USE_DSHOT_DMAR
-burstDmaTimer_t burstDmaTimers[MAX_DMA_TIMERS];
-uint8_t burstDmaTimersCount = 0;
-
 static uint8_t getBurstDmaTimerIndex(TIM_TypeDef *timer)
 {
     for (int i = 0; i < burstDmaTimersCount; i++) {

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.h

@@ -138,6 +138,7 @@ typedef enum {
     TCH_DMA_IDLE = 0,
     TCH_DMA_READY,
     TCH_DMA_ACTIVE,
+    TCH_DMA_CIRCULAR,
 } tchDmaState_e;
 
 // Some forward declarations for types

src/main/drivers/timer_impl.h

@@ -84,8 +84,10 @@ 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, uint32_t dmaBufferSize);
 
 #ifdef USE_DSHOT_DMAR
 bool impl_timerPWMConfigDMABurst(burstDmaTimer_t *burstDmaTimer, TCH_t * tch, void * dmaBuffer, uint8_t dmaBufferElementSize, uint32_t dmaBufferElementCount);
 void impl_pwmBurstDMAStart(burstDmaTimer_t * burstDmaTimer, uint32_t BurstLength);
+void impl_pwmBurstDMASetCircular(burstDmaTimer_t * burstDmaTimer, TCH_t * tch, bool circular, uint32_t dmaBufferSize);
 #endif

src/main/drivers/timer_impl_hal.c

@@ -319,6 +319,12 @@ static void impl_timerDMA_IRQHandler(DMA_t descriptor)
     if (DMA_GET_FLAG_STATUS(descriptor, DMA_IT_TCIF)) {
         TCH_t * tch = (TCH_t *)descriptor->userParam;
 
+        // In circular mode, let DMA keep running - don't disable the stream
+        if (tch->dmaState == TCH_DMA_CIRCULAR) {
+            DMA_CLEAR_FLAG(descriptor, DMA_IT_TCIF);
+            return;
+        }
+
         // If it was ACTIVE - switch to IDLE
         if (tch->dmaState == TCH_DMA_ACTIVE) {
             tch->dmaState = TCH_DMA_IDLE;
@@ -512,6 +518,46 @@ void impl_pwmBurstDMAStart(burstDmaTimer_t * burstDmaTimer, uint32_t BurstLength
     //LL_TIM_EnableDMAReq_UPDATE(burstDmaTimer->timer);
     LL_TIM_EnableDMAReq_CCx(burstDmaTimer->timer, burstDmaTimer->burstRequestSource);
 }
+
+void impl_pwmBurstDMASetCircular(burstDmaTimer_t * burstDmaTimer, TCH_t * tch, bool circular, uint32_t dmaBufferSize)
+{
+    if (!tch->dma || !tch->dma->dma) {
+        return;
+    }
+
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        LL_TIM_DisableDMAReq_CCx(burstDmaTimer->timer, burstDmaTimer->burstRequestSource);
+        LL_DMA_DisableStream(burstDmaTimer->dma, burstDmaTimer->streamLL);
+
+        uint32_t timeout = 10000;
+        while (LL_DMA_IsEnabledStream(burstDmaTimer->dma, burstDmaTimer->streamLL) && timeout--) {
+            __NOP();
+        }
+
+        if (LL_DMA_IsEnabledStream(burstDmaTimer->dma, burstDmaTimer->streamLL)) {
+            LL_TIM_EnableDMAReq_CCx(burstDmaTimer->timer, burstDmaTimer->burstRequestSource);
+            return;
+        }
+
+        DMA_CLEAR_FLAG(tch->dma, DMA_IT_TCIF);
+
+        if (circular) {
+            LL_DMA_SetMode(burstDmaTimer->dma, burstDmaTimer->streamLL, LL_DMA_MODE_CIRCULAR);
+            LL_DMA_SetDataLength(burstDmaTimer->dma, burstDmaTimer->streamLL, dmaBufferSize);
+            LL_DMA_DisableIT_TC(burstDmaTimer->dma, burstDmaTimer->streamLL);
+            tch->dmaState = TCH_DMA_CIRCULAR;
+        } else {
+            LL_DMA_SetMode(burstDmaTimer->dma, burstDmaTimer->streamLL, LL_DMA_MODE_NORMAL);
+            LL_DMA_EnableIT_TC(burstDmaTimer->dma, burstDmaTimer->streamLL);
+            tch->dmaState = TCH_DMA_IDLE;
+        }
+
+        __DSB();
+
+        LL_DMA_EnableStream(burstDmaTimer->dma, burstDmaTimer->streamLL);
+        LL_TIM_EnableDMAReq_CCx(burstDmaTimer->timer, burstDmaTimer->burstRequestSource);
+    }
+}
 #endif
 
 void impl_timerPWMPrepareDMA(TCH_t * tch, uint32_t dmaBufferElementCount)
@@ -580,3 +626,52 @@ void impl_timerPWMStopDMA(TCH_t * tch)
 
     HAL_TIM_Base_Start(tch->timCtx->timHandle);
 }
+
+void impl_timerPWMSetDMACircular(TCH_t * tch, bool circular, uint32_t dmaBufferSize)
+{
+    if (!tch->dma || !tch->dma->dma) {
+        return;
+    }
+
+    const uint32_t streamLL = lookupDMALLStreamTable[DMATAG_GET_STREAM(tch->timHw->dmaTag)];
+    DMA_TypeDef *dmaBase = tch->dma->dma;
+
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        // Stop new transfer triggers before reconfiguring
+        LL_TIM_DisableDMAReq_CCx(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex]);
+        LL_DMA_DisableStream(dmaBase, streamLL);
+
+        // STM32H7 RM: poll EN bit until stream is actually disabled
+        uint32_t timeout = 10000; // ~20us at 480MHz, well above worst-case disable latency
+        while (LL_DMA_IsEnabledStream(dmaBase, streamLL) && timeout--) {
+            __NOP();
+        }
+
+        if (LL_DMA_IsEnabledStream(dmaBase, streamLL)) {
+            LL_TIM_EnableDMAReq_CCx(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex]);
+            return;
+        }
+
+        DMA_CLEAR_FLAG(tch->dma, DMA_IT_TCIF);
+
+        if (circular) {
+            LL_DMA_SetMode(dmaBase, streamLL, LL_DMA_MODE_CIRCULAR);
+            // Circular mode requires non-zero NDTR (STM32H7 RM constraint)
+            LL_DMA_SetDataLength(dmaBase, streamLL, dmaBufferSize);
+            // Disable TC interrupt — in circular mode, TC fires every cycle
+            // and the IRQ handler would otherwise disable the stream
+            LL_DMA_DisableIT_TC(dmaBase, streamLL);
+            tch->dmaState = TCH_DMA_CIRCULAR;
+        } else {
+            LL_DMA_SetMode(dmaBase, streamLL, LL_DMA_MODE_NORMAL);
+            LL_DMA_EnableIT_TC(dmaBase, streamLL);
+            tch->dmaState = TCH_DMA_IDLE;
+        }
+
+        // Ensure register writes are visible to DMA before re-enabling
+        __DSB();
+
+        LL_DMA_EnableStream(dmaBase, streamLL);
+        LL_TIM_EnableDMAReq_CCx(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex]);
+    }
+}

src/main/drivers/timer_impl_stdperiph.c

@@ -270,6 +270,13 @@ static void impl_timerDMA_IRQHandler(DMA_t descriptor)
 {
     if (DMA_GET_FLAG_STATUS(descriptor, DMA_IT_TCIF)) {
         TCH_t * tch = (TCH_t *)descriptor->userParam;
+
+        // In circular mode, let DMA keep running - don't disable the stream
+        if (tch->dmaState == TCH_DMA_CIRCULAR) {
+            DMA_CLEAR_FLAG(descriptor, DMA_IT_TCIF);
+            return;
+        }
+
         tch->dmaState = TCH_DMA_IDLE;
 
         DMA_Cmd(tch->dma->ref, DISABLE);
@@ -463,6 +470,46 @@ void impl_pwmBurstDMAStart(burstDmaTimer_t * burstDmaTimer, uint32_t BurstLength
     TIM_DMAConfig(burstDmaTimer->timer, TIM_DMABase_CCR1, TIM_DMABurstLength_4Transfers);
     TIM_DMACmd(burstDmaTimer->timer, burstDmaTimer->burstRequestSource, ENABLE);
 }
+
+void impl_pwmBurstDMASetCircular(burstDmaTimer_t * burstDmaTimer, TCH_t * tch, bool circular, uint32_t dmaBufferSize)
+{
+    if (!tch->dma || !tch->dma->ref) {
+        return;
+    }
+
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        TIM_DMACmd(burstDmaTimer->timer, burstDmaTimer->burstRequestSource, DISABLE);
+        DMA_Cmd(burstDmaTimer->dmaBurstStream, DISABLE);
+
+        uint32_t timeout = 10000;
+        while ((burstDmaTimer->dmaBurstStream->CR & DMA_SxCR_EN) && timeout--) {
+            __NOP();
+        }
+
+        if (burstDmaTimer->dmaBurstStream->CR & DMA_SxCR_EN) {
+            TIM_DMACmd(burstDmaTimer->timer, burstDmaTimer->burstRequestSource, ENABLE);
+            return;
+        }
+
+        DMA_CLEAR_FLAG(tch->dma, DMA_IT_TCIF);
+
+        if (circular) {
+            burstDmaTimer->dmaBurstStream->CR |= DMA_SxCR_CIRC;
+            DMA_SetCurrDataCounter(burstDmaTimer->dmaBurstStream, dmaBufferSize);
+            DMA_ITConfig(burstDmaTimer->dmaBurstStream, DMA_IT_TC, DISABLE);
+            tch->dmaState = TCH_DMA_CIRCULAR;
+        } else {
+            burstDmaTimer->dmaBurstStream->CR &= ~DMA_SxCR_CIRC;
+            DMA_ITConfig(burstDmaTimer->dmaBurstStream, DMA_IT_TC, ENABLE);
+            tch->dmaState = TCH_DMA_IDLE;
+        }
+
+        __DSB();
+
+        DMA_Cmd(burstDmaTimer->dmaBurstStream, ENABLE);
+        TIM_DMACmd(burstDmaTimer->timer, burstDmaTimer->burstRequestSource, ENABLE);
+    }
+}
 #endif
 
 void impl_timerPWMPrepareDMA(TCH_t * tch, uint32_t dmaBufferElementCount)
@@ -519,3 +566,48 @@ 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, uint32_t dmaBufferSize)
+{
+    if (!tch->dma || !tch->dma->ref) {
+        return;
+    }
+
+    ATOMIC_BLOCK(NVIC_PRIO_MAX) {
+        // Stop new transfer triggers before reconfiguring
+        TIM_DMACmd(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex], DISABLE);
+        DMA_Cmd(tch->dma->ref, DISABLE);
+
+        // STM32F4/F7 RM: poll EN bit until stream is actually disabled
+        uint32_t timeout = 10000; // ~60us at 168MHz, well above worst-case disable latency
+        while ((tch->dma->ref->CR & DMA_SxCR_EN) && timeout--) {
+            __NOP();
+        }
+
+        if (tch->dma->ref->CR & DMA_SxCR_EN) {
+            TIM_DMACmd(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex], ENABLE);
+            return;
+        }
+
+        DMA_CLEAR_FLAG(tch->dma, DMA_IT_TCIF);
+
+        if (circular) {
+            tch->dma->ref->CR |= DMA_SxCR_CIRC;
+            DMA_SetCurrDataCounter(tch->dma->ref, dmaBufferSize);
+            // Disable TC interrupt — in circular mode, TC fires every cycle
+            // and the IRQ handler would otherwise disable the stream
+            DMA_ITConfig(tch->dma->ref, DMA_IT_TC, DISABLE);
+            tch->dmaState = TCH_DMA_CIRCULAR;
+        } else {
+            tch->dma->ref->CR &= ~DMA_SxCR_CIRC;
+            DMA_ITConfig(tch->dma->ref, DMA_IT_TC, ENABLE);
+            tch->dmaState = TCH_DMA_IDLE;
+        }
+
+        // Ensure register writes are visible to DMA before re-enabling
+        __DSB();
+
+        DMA_Cmd(tch->dma->ref, ENABLE);
+        TIM_DMACmd(tch->timHw->tim, lookupDMASourceTable[tch->timHw->channelIndex], ENABLE);
+    }
+}