From dd8115c9b4f99a89feef455d16b2b141b36ee253 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Sun, 10 Feb 2019 21:05:23 +1100
Subject: [PATCH] HAL_ChibiOS: check for already allocated TX dma in UART
 driver

---
 libraries/AP_HAL_ChibiOS/UARTDriver.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libraries/AP_HAL_ChibiOS/UARTDriver.cpp b/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
index 6fbdcc618b..fb50d22eca 100644
--- a/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
+++ b/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
@@ -314,7 +314,9 @@ void UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
 void UARTDriver::dma_tx_allocate(Shared_DMA *ctx)
 {
 #if HAL_USE_SERIAL == TRUE
-    osalDbgAssert(txdma == nullptr, "double DMA allocation");
+    if (txdma != nullptr) {
+        return;
+    }
     chSysLock();
     txdma = dmaStreamAllocI(sdef.dma_tx_stream_id,
                             12,  //IRQ Priority