From fc0b2ef920d4df1e2e608dabadb915c6fc953522 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Fri, 20 Mar 2020 10:03:16 +1100
Subject: [PATCH] HAL_ChibiOS: added half-duplex protection for non-inverted

to prevent output bytes being seen as input bytes we disable half
duplex during transmit. This was previously only done for non-inverted
UARTs. This patch enables it whether we are inverted or not. This
greatly reduces the number of bad input bytes.
---
 libraries/AP_HAL_ChibiOS/UARTDriver.cpp | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/libraries/AP_HAL_ChibiOS/UARTDriver.cpp b/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
index bb331c51613..29557864bee 100644
--- a/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
+++ b/libraries/AP_HAL_ChibiOS/UARTDriver.cpp
@@ -929,12 +929,10 @@ void UARTDriver::half_duplex_setup_tx(void)
     if (!hd_tx_active) {
         chEvtGetAndClearFlags(&hd_listener);
         hd_tx_active = true;
-        if (_last_options & (OPTION_RXINV | OPTION_TXINV)) {
-            SerialDriver *sd = (SerialDriver*)(sdef.serial);
-            sdStop(sd);
-            sercfg.cr3 &= ~USART_CR3_HDSEL;
-            sdStart(sd, &sercfg);
-        }
+        SerialDriver *sd = (SerialDriver*)(sdef.serial);
+        sdStop(sd);
+        sercfg.cr3 &= ~USART_CR3_HDSEL;
+        sdStart(sd, &sercfg);
     }
 #endif
 }
@@ -955,12 +953,10 @@ void UARTDriver::_timer_tick(void)
           half-duplex transmit has finished. We now re-enable the
           HDSEL bit for receive
          */
-        if (_last_options & (OPTION_RXINV | OPTION_TXINV)) {
-            SerialDriver *sd = (SerialDriver*)(sdef.serial);
-            sdStop(sd);
-            sercfg.cr3 |= USART_CR3_HDSEL;
-            sdStart(sd, &sercfg);
-        }
+        SerialDriver *sd = (SerialDriver*)(sdef.serial);
+        sdStop(sd);
+        sercfg.cr3 |= USART_CR3_HDSEL;
+        sdStart(sd, &sercfg);
         hd_tx_active = false;
     }
 #endif