AP_HAL: Add support for parity to Serial passthrough

Add code to reflect USB ACM parity setting to the passthrough port alongside existing support for ACM baud rate changes.  Some use cases for serial passthrough require specific parity settings.

For example, even parity is used and required by the USART protocol used in the STM32 system bootloader. This enhancement allows the use of standard flash programming tools such as STM32CubeProgrammer to flash connected STM based peripherals such as Receivers and Telemetry radios via serial passthrough.  Some examples of such peripherals include the FrSky R9 receivers as well as various other STM based LoRa modules used by the mLRS project.

libraries/AP_HAL/UARTDriver.cpp

@@ -179,6 +179,11 @@ bool AP_HAL::UARTDriver::flow_control_enabled(enum flow_control flow_control_set
     return false;
 }
 
+uint8_t AP_HAL::UARTDriver::get_parity(void)
+{
+    return AP_HAL::UARTDriver::parity;
+}
+
 #if HAL_UART_STATS_ENABLED
 // Take cumulative bytes and return the change since last call
 uint32_t AP_HAL::UARTDriver::StatsTracker::ByteTracker::update(uint32_t bytes)

libraries/AP_HAL/UARTDriver.h

@@ -78,6 +78,9 @@ public:
 
     // read buffer from a locked port. If port is locked and key is not correct then -1 is returned
     ssize_t read_locked(uint8_t *buf, size_t count, uint32_t key) WARN_IF_UNUSED;
+
+    // get current parity for passthrough use
+    uint8_t get_parity(void);
     
     // control optional features
     virtual bool set_options(uint16_t options) { _last_options = options; return options==0; }
@@ -189,6 +192,9 @@ public:
     // return true requested baud on USB port
     virtual uint32_t get_usb_baud(void) const { return 0; }
 
+    // return requested parity on USB port
+    virtual uint8_t get_usb_parity(void) const { return parity; }
+
     // disable TX/RX pins for unusued uart
     virtual void disable_rxtx(void) const {}
 
@@ -213,6 +219,8 @@ protected:
     uint32_t lock_write_key;
     uint32_t lock_read_key;
 
+    uint8_t parity;
+
     /*
       backend begin method
      */

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -672,6 +672,19 @@ uint32_t UARTDriver::get_usb_baud() const
     return 0;
 }
 
+/*
+    get the requested usb parity.  Valid if get_usb_baud() returned non-zero.
+*/
+uint8_t UARTDriver::get_usb_parity() const
+{
+#if HAL_USE_SERIAL_USB
+    if (sdef.is_usb) {
+        return ::get_usb_parity(sdef.endpoint_id);
+    }
+#endif
+    return 0;
+}
+
 uint32_t UARTDriver::_available()
 {
     if (!_rx_initialised || _uart_owner_thd != chThdGetSelfX()) {
@@ -1429,6 +1442,7 @@ void UARTDriver::configure_parity(uint8_t v)
         // not possible
         return;
     }
+    UARTDriver::parity = v;
 #if HAL_USE_SERIAL == TRUE
     // stop and start to take effect
     sdStop((SerialDriver*)sdef.serial);

libraries/AP_HAL_ChibiOS/UARTDriver.h

@@ -38,6 +38,7 @@ public:
     bool is_initialized() override;
     bool tx_pending() override;
     uint32_t get_usb_baud() const override;
+    uint8_t get_usb_parity() const override;
 
     // disable TX/RX pins for unusued uart
     void disable_rxtx(void) const override;

libraries/AP_HAL_ChibiOS/hwdef/common/usbcfg.c

@@ -251,6 +251,18 @@ uint32_t get_usb_baud(uint16_t endpoint_id)
     }
     return 0;
 }
+
+/*
+    get the requested usb parity.  Valid if get_usb_baud() returned non-zero
+*/
+uint8_t get_usb_parity(uint16_t endpoint_id)
+{
+      if (endpoint_id == 0) {
+          return linecoding.bParityType;
+      }
+
+      return 0;
+}
 #endif
 /**
  * @brief   IN EP1 state.

libraries/AP_HAL_ChibiOS/hwdef/common/usbcfg.h

@@ -46,6 +46,7 @@ extern SerialUSBDriver SDU2;
 extern const SerialUSBConfig serusbcfg2;
 #endif //HAL_HAVE_DUAL_USB_CDC
 uint32_t get_usb_baud(uint16_t endpoint_id);
+uint8_t get_usb_parity(uint16_t endpoint_id);
 #endif
 #define USB_DESC_MAX_STRLEN 100
 void setup_usb_strings(void);

libraries/AP_HAL_ChibiOS/hwdef/common/usbcfg_dualcdc.c

@@ -315,6 +315,19 @@ uint32_t get_usb_baud(uint16_t endpoint_id)
   }
   return 0;
 }
+
+/*
+    get the requested usb parity.  Valid if get_usb_baud() returned non-zero
+*/
+uint8_t get_usb_parity(uint16_t endpoint_id)
+{
+  for (uint8_t i = 0; i < ARRAY_SIZE(linecoding); i++) {
+      if (endpoint_id == ep_index[i]) {
+          return linecoding[i].bParityType;
+      }
+  }
+  return 0;
+}
 #endif
 /**
  * @brief   IN EP1 state.

libraries/AP_HAL_Linux/UARTDriver.cpp

@@ -417,6 +417,7 @@ void UARTDriver::_timer_tick(void)
 }
 
 void UARTDriver::configure_parity(uint8_t v) {
+    UARTDriver::parity = v;
     _device->set_parity(v);
 }
 

libraries/AP_HAL_SITL/UARTDriver.h

@@ -161,6 +161,7 @@ private:
     // statistics
     uint32_t _tx_stats_bytes;
     uint32_t _rx_stats_bytes;
+
 };
 
 #endif

libraries/AP_HAL_SITL/UART_utils.cpp

@@ -73,6 +73,7 @@ void HALSITL::UARTDriver::configure_parity(uint8_t v)
     if (_fd < 0) {
         return;
     }
+    UARTDriver::parity = v;
 #ifdef USE_TERMIOS
     struct termios t;