From bb423bc0075b8209cdcd26e6e2c3306a7857aa4f Mon Sep 17 00:00:00 2001
From: Jacob Dahl <37091262+dakejahl@users.noreply.github.com>
Date: Tue, 10 Jun 2025 00:36:45 -0800
Subject: [PATCH] dshot: fix bidirectional dshot stream sharing (#24996)

Freeing the DMA stream in the hrt callback causes other peripherals on that DMA controller to lock up (namely GPS). Moving the free back into thread context, right before allocation, solves the problem
---
 .../src/px4/stm/stm32_common/dshot/dshot.c    | 36 +++++++++++--------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/platforms/nuttx/src/px4/stm/stm32_common/dshot/dshot.c b/platforms/nuttx/src/px4/stm/stm32_common/dshot/dshot.c
index 48e12dd8f7..1ec91f28a2 100644
--- a/platforms/nuttx/src/px4/stm/stm32_common/dshot/dshot.c
+++ b/platforms/nuttx/src/px4/stm/stm32_common/dshot/dshot.c
@@ -206,7 +206,7 @@ static void init_timers_dma_up(void)
 		timer_configs[timer_index].dma_handle = stm32_dmachannel(io_timers[timer_index].dshot.dma_map_up);
 
 		if (timer_configs[timer_index].dma_handle == NULL) {
-			PX4_DEBUG("Failed to allocate Timer %u DMA UP", timer_index);
+			PX4_WARN("Failed to allocate Timer %u DMA UP", timer_index);
 			continue;
 		}
 
@@ -214,12 +214,16 @@ static void init_timers_dma_up(void)
 		timer_configs[timer_index].initialized = true;
 	}
 
-	// Free the allocated DMA channels
-	for (uint8_t timer_index = 0; timer_index < MAX_IO_TIMERS; timer_index++) {
-		if (timer_configs[timer_index].dma_handle != NULL) {
-			stm32_dmafree(timer_configs[timer_index].dma_handle);
-			timer_configs[timer_index].dma_handle = NULL;
-			PX4_INFO("Freed DMA UP Timer Index %u", timer_index);
+	// Bidirectional DShot will free/allocate DMA stream on every update event. This is required
+	// in order to reconfigure the DMA stream between Timer Burst and CaptureCompare.
+	if (_bidirectional) {
+		// Free the allocated DMA channels
+		for (uint8_t timer_index = 0; timer_index < MAX_IO_TIMERS; timer_index++) {
+			if (timer_configs[timer_index].dma_handle != NULL) {
+				stm32_dmafree(timer_configs[timer_index].dma_handle);
+				timer_configs[timer_index].dma_handle = NULL;
+				PX4_INFO("Freed DMA UP Timer Index %u", timer_index);
+			}
 		}
 	}
 }
@@ -341,8 +345,15 @@ void up_dshot_trigger()
 
 			io_timer_set_dshot_burst_mode(timer_index, _dshot_frequency, channel_count);
 
-			// Allocate DMA
-			if (timer_configs[timer_index].dma_handle == NULL) {
+			if (_bidirectional) {
+				// Deallocate DMA from previous transaction
+				if (timer_configs[timer_index].dma_handle != NULL) {
+					stm32_dmastop(timer_configs[timer_index].dma_handle);
+					stm32_dmafree(timer_configs[timer_index].dma_handle);
+					timer_configs[timer_index].dma_handle = NULL;
+				}
+
+				// Allocate DMA
 				timer_configs[timer_index].dma_handle = stm32_dmachannel(io_timers[timer_index].dshot.dma_map_up);
 
 				if (timer_configs[timer_index].dma_handle == NULL) {
@@ -502,11 +513,8 @@ static void capture_complete_callback(void *arg)
 	// Disable capture DMA
 	io_timer_capture_dma_req(timer_index, capture_channel, false);
 
-	if (timer_configs[timer_index].dma_handle != NULL) {
-		stm32_dmastop(timer_configs[timer_index].dma_handle);
-		stm32_dmafree(timer_configs[timer_index].dma_handle);
-		timer_configs[timer_index].dma_handle = NULL;
-	}
+	// Stop DMA (should already be finished)
+	stm32_dmastop(timer_configs[timer_index].dma_handle);
 
 	// Re-initialize all output channels on this timer
 	for (uint8_t output_channel = 0; output_channel < MAX_TIMER_IO_CHANNELS; output_channel++) {