From 0545087008b4791d63badcd59ac7e09b0de6f2b4 Mon Sep 17 00:00:00 2001
From: Mark Haslinghuis <mark@numloq.nl>
Date: Sat, 21 Oct 2023 14:35:13 +0200
Subject: [PATCH] Check tx on MSP and GPS only (#13113)

---
 src/main/drivers/serial.h                | 3 +++
 src/main/drivers/serial_uart_stm32f4xx.c | 2 +-
 src/main/drivers/serial_uart_stm32f7xx.c | 2 +-
 src/main/drivers/serial_uart_stm32g4xx.c | 2 +-
 src/main/drivers/serial_uart_stm32h7xx.c | 2 +-
 src/main/io/gps.c                        | 8 +++++++-
 src/main/msp/msp_serial.c                | 2 ++
 7 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/main/drivers/serial.h b/src/main/drivers/serial.h
index 2f63e596ae..f178975e37 100644
--- a/src/main/drivers/serial.h
+++ b/src/main/drivers/serial.h
@@ -53,6 +53,9 @@ typedef enum {
     SERIAL_BIDIR_PP        = 1 << 4,
     SERIAL_BIDIR_NOPULL    = 1 << 5, // disable pulls in BIDIR RX mode
     SERIAL_BIDIR_PP_PD     = 1 << 6, // PP mode, normall inverted, but with PullDowns, to fix SA after bidir issue fixed (#10220)
+
+    // If this option is set then switch the TX line to input when not in use to detect it being pulled low
+    SERIAL_CHECK_TX        = 1 << 7,
 } portOptions_e;
 
 // Define known line control states which may be passed up by underlying serial driver callback
diff --git a/src/main/drivers/serial_uart_stm32f4xx.c b/src/main/drivers/serial_uart_stm32f4xx.c
index 384948689f..57f6b607d7 100644
--- a/src/main/drivers/serial_uart_stm32f4xx.c
+++ b/src/main/drivers/serial_uart_stm32f4xx.c
@@ -340,7 +340,7 @@ uartPort_t *serialUART(UARTDevice_e device, uint32_t baudRate, portMode_e mode,
         if ((mode & MODE_TX) && txIO) {
             IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
 
-            if ((options & SERIAL_INVERTED) == SERIAL_NOT_INVERTED) {
+            if (options & SERIAL_CHECK_TX) {
                 uart->txPinState = TX_PIN_ACTIVE;
                 // Switch TX to an input with pullup so it's state can be monitored
                 uartTxMonitor(s);
diff --git a/src/main/drivers/serial_uart_stm32f7xx.c b/src/main/drivers/serial_uart_stm32f7xx.c
index 3782dd43ba..a63ff201d2 100644
--- a/src/main/drivers/serial_uart_stm32f7xx.c
+++ b/src/main/drivers/serial_uart_stm32f7xx.c
@@ -376,7 +376,7 @@ uartPort_t *serialUART(UARTDevice_e device, uint32_t baudRate, portMode_e mode,
         if ((mode & MODE_TX) && txIO) {
             IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
 
-            if ((options & SERIAL_INVERTED) == SERIAL_NOT_INVERTED) {
+            if (options & SERIAL_CHECK_TX) {
                 uartdev->txPinState = TX_PIN_MONITOR;
                 // Switch TX to UART output whilst UART sends idle preamble
                 checkUsartTxOutput(s);
diff --git a/src/main/drivers/serial_uart_stm32g4xx.c b/src/main/drivers/serial_uart_stm32g4xx.c
index d8a87c792c..1a75f16493 100644
--- a/src/main/drivers/serial_uart_stm32g4xx.c
+++ b/src/main/drivers/serial_uart_stm32g4xx.c
@@ -309,7 +309,7 @@ uartPort_t *serialUART(UARTDevice_e device, uint32_t baudRate, portMode_e mode,
         if ((mode & MODE_TX) && txIO) {
             IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
 
-            if ((options & SERIAL_INVERTED) == SERIAL_NOT_INVERTED) {
+            if (options & SERIAL_CHECK_TX) {
                 uartdev->txPinState = TX_PIN_ACTIVE;
                 // Switch TX to an input with pullup so it's state can be monitored
                 uartTxMonitor(s);
diff --git a/src/main/drivers/serial_uart_stm32h7xx.c b/src/main/drivers/serial_uart_stm32h7xx.c
index e3b3962b99..c21a908d4d 100644
--- a/src/main/drivers/serial_uart_stm32h7xx.c
+++ b/src/main/drivers/serial_uart_stm32h7xx.c
@@ -486,7 +486,7 @@ uartPort_t *serialUART(UARTDevice_e device, uint32_t baudRate, portMode_e mode,
         if ((mode & MODE_TX) && txIO) {
             IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
 
-            if ((options & SERIAL_INVERTED) == SERIAL_NOT_INVERTED) {
+            if (options & SERIAL_CHECK_TX) {
                 uartdev->txPinState = TX_PIN_ACTIVE;
                 // Switch TX to an input with pullup so it's state can be monitored
                 uartTxMonitor(s);
diff --git a/src/main/io/gps.c b/src/main/io/gps.c
index a89b6fb30a..a399898e26 100644
--- a/src/main/io/gps.c
+++ b/src/main/io/gps.c
@@ -338,14 +338,20 @@ void gpsInit(void)
     }
 
     portMode_e mode = MODE_RXTX;
+    portOptions_e options = SERIAL_NOT_INVERTED;
+
 #if defined(GPS_NMEA_TX_ONLY)
     if (gpsConfig()->provider == GPS_NMEA) {
         mode &= ~MODE_TX;
     }
 #endif
 
+    if ((gpsPortConfig->identifier >= SERIAL_PORT_USART1) && (gpsPortConfig->identifier <= SERIAL_PORT_USART10)){
+        options |= SERIAL_CHECK_TX;
+    }
+
     // no callback - buffer will be consumed in gpsUpdate()
-    gpsPort = openSerialPort(gpsPortConfig->identifier, FUNCTION_GPS, NULL, NULL, baudRates[gpsInitData[gpsData.baudrateIndex].baudrateIndex], mode, SERIAL_NOT_INVERTED);
+    gpsPort = openSerialPort(gpsPortConfig->identifier, FUNCTION_GPS, NULL, NULL, baudRates[gpsInitData[gpsData.baudrateIndex].baudrateIndex], mode, options);
     if (!gpsPort) {
         return;
     }
diff --git a/src/main/msp/msp_serial.c b/src/main/msp/msp_serial.c
index 08b1c0ba6d..dbae687672 100644
--- a/src/main/msp/msp_serial.c
+++ b/src/main/msp/msp_serial.c
@@ -69,6 +69,8 @@ void mspSerialAllocatePorts(void)
 
         if (mspConfig()->halfDuplex) {
             options |= SERIAL_BIDIR;
+        } else if ((portConfig->identifier >= SERIAL_PORT_USART1) && (portConfig->identifier <= SERIAL_PORT_USART10)){
+            options |= SERIAL_CHECK_TX;
         }
 
         serialPort_t *serialPort = openSerialPort(portConfig->identifier, FUNCTION_MSP, NULL, NULL, baudRates[portConfig->msp_baudrateIndex], MODE_RXTX, options);