AP_HAL_ChibiOS: allow setup for low noise clock mismatch tolerant UART line

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -455,6 +455,13 @@ void UARTDriver::_begin(uint32_t b, uint16_t rxS, uint16_t txS)
                 sercfg.cr3 |= USART_CR3_DMAT;
             }
             sercfg.irq_cb = rx_irq_cb;
+#if HAL_HAVE_LOW_NOISE_UART
+            if (sdef.low_noise_line) {
+                // we can mark UART to sample on one bit instead of default 3 bits
+                // this allows us to be slightly less sensitive to clock differences
+                sercfg.cr3 |= USART_CR3_ONEBIT;
+            }
+#endif
 #endif // HAL_UART_NODMA
             if (!(sercfg.cr2 & USART_CR2_STOP2_BITS)) {
                 sercfg.cr2 |= USART_CR2_STOP1_BITS;

libraries/AP_HAL_ChibiOS/UARTDriver.h

@@ -28,6 +28,10 @@
 // enough for serial0 to serial9, plus IOMCU
 #define UART_MAX_DRIVERS 11
 
+#ifndef HAL_HAVE_LOW_NOISE_UART
+#define HAL_HAVE_LOW_NOISE_UART 0
+#endif
+
 class ChibiOS::UARTDriver : public AP_HAL::UARTDriver {
 public:
     UARTDriver(uint8_t serial_num);
@@ -79,7 +83,10 @@ public:
         uint8_t get_index(void) const {
             return uint8_t(this - &_serial_tab[0]);
         }
+
+#if HAL_HAVE_LOW_NOISE_UART
         bool low_noise_line;
+#endif
     };
 
     bool wait_timeout(uint16_t n, uint32_t timeout_ms) override;

libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py

@@ -1865,6 +1865,7 @@ INCLUDE common.ld
         OTG2_index = None
         devlist = []
         have_rts_cts = False
+        have_low_noise = False
         crash_uart = None
 
         # write config for CrashCatcher UART
@@ -1878,6 +1879,14 @@ INCLUDE common.ld
             f.write('#define IRQ_DISABLE_HAL_CRASH_SERIAL_PORT() nvicDisableVector(STM32_%s_NUMBER)\n' % crash_uart)
             f.write('#define RCC_RESET_HAL_CRASH_SERIAL_PORT() rccReset%s(); rccEnable%s(true)\n' % (crash_uart, crash_uart))
             f.write('#define HAL_CRASH_SERIAL_PORT_CLOCK STM32_%sCLK\n' % crash_uart)
+        # check if we have a UART with a low noise RX pin
+        for num, dev in enumerate(serial_list):
+            if not dev.startswith('UART') and not dev.startswith('USART'):
+                continue
+            rx_port = dev + '_RX'
+            if rx_port in self.bylabel and self.bylabel[rx_port].has_extra('LOW_NOISE'):
+                have_low_noise = True
+                break
         for num, dev in enumerate(serial_list):
             if dev.startswith('UART'):
                 n = int(dev[4:])
@@ -1904,12 +1913,20 @@ INCLUDE common.ld
 
             if dev.startswith('OTG2'):
                 f.write(
-                    '#define HAL_%s_CONFIG {(BaseSequentialStream*) &SDU2, 2, true, false, 0, 0, false, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, UINT8_MAX}\n' % dev)  # noqa
+                    '#define HAL_%s_CONFIG {(BaseSequentialStream*) &SDU2, 2, true, false, 0, 0, false, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, UINT8_MAX,' % dev)  # noqa
+                if have_low_noise:
+                    f.write('false}\n')
+                else:
+                    f.write('}\n')
                 OTG2_index = serial_list.index(dev)
                 self.dual_USB_enabled = True
             elif dev.startswith('OTG'):
                 f.write(
-                    '#define HAL_%s_CONFIG {(BaseSequentialStream*) &SDU1, 1, true, false, 0, 0, false, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, UINT8_MAX}\n' % dev)  # noqa
+                    '#define HAL_%s_CONFIG {(BaseSequentialStream*) &SDU1, 1, true, false, 0, 0, false, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, UINT8_MAX,' % dev)  # noqa
+                if have_low_noise:
+                    f.write('false}\n')
+                else:
+                    f.write('}\n')
             else:
                 need_uart_driver = True
                 f.write(
@@ -1948,9 +1965,17 @@ INCLUDE common.ld
                             if s not in lib.AltFunction_map:
                                 return "UINT8_MAX"
                             return lib.AltFunction_map[s]
+                if have_low_noise:
+                    low_noise = 'false'
+                    rx_port = dev + '_RX'
+                    if rx_port in self.bylabel and self.bylabel[rx_port].has_extra('LOW_NOISE'):
+                        low_noise = 'true'
+                    f.write("%s, %s}\n" % (get_RTS_alt_function(), low_noise))
+                else:
+                    f.write("%s}\n" % get_RTS_alt_function())
 
-                f.write("%s}\n" % get_RTS_alt_function())
+        if have_low_noise:
-
+            f.write('#define HAL_HAVE_LOW_NOISE_UART 1\n')
         if have_rts_cts:
             f.write('#define AP_FEATURE_RTSCTS 1\n')
         if OTG2_index is not None: