bsp: mcxn947: fix dead console RX on LPUART

LPUART_Init re-ran LP_FLEXCOMM_Init on every configure, resetting the
peripheral and wiping CTRL.RIE set by RT_DEVICE_CTRL_SET_INT, so the
console never received a byte and host-side VCOM writes wedged.

Verified on FRDM-MCXN947 hardware via GDB: NVIC ISER never armed and a
hardware breakpoint on uart_isr never fired until these changes.

- define LPFLEXCOMM_INIT_NOT_USED_IN_DRIVER=1 so fsl drivers stop
  re-initialising the FlexComm on every configure
- select FlexComm function once in rt_hw_flexcomm_mode_init()
- preserve/restore RX interrupt enable across LPUART_Init (PR #11186)
- clear OR/FE/NF/PF in uart_isr: an uncleared overrun inhibits all
  further LPUART reception

Reintroduces the drv_uart.c fix from #11186 (reverted in #11191),
combined with the one-time FlexComm mode selection that makes it safe.

Signed-off-by: Alexander Salas Bastidas <ajsb85@firechip.dev>

Author: ajsb85

bsp/nxp/mcx/mcxn/Libraries/drivers/drv_uart.c

@@ -160,7 +160,18 @@ static rt_err_t mcx_configure(struct rt_serial_device *serial, struct serial_con
     config.enableTx     = true;
     config.enableRx     = true;
 
-    LPUART_Init(uart->uart_base, &config, CLOCK_GetFreq(uart->clock_src));
+    /* LPUART_Init resets the peripheral, wiping any RX interrupt enable set
+     * by a prior RT_DEVICE_CTRL_SET_INT (upstream fix, PR #11186). Preserve
+     * and restore it, or console RX goes permanently dead. */
+    {
+        rt_uint32_t irq_regval = LPUART_GetEnabledInterrupts(uart->uart_base);
+        LPUART_Init(uart->uart_base, &config, CLOCK_GetFreq(uart->clock_src));
+        if (irq_regval & kLPUART_RxDataRegFullInterruptEnable)
+        {
+            LPUART_EnableInterrupts(uart->uart_base, kLPUART_RxDataRegFullInterruptEnable);
+            EnableIRQ(uart->irqn);
+        }
+    }
 
     return RT_EOK;
 }
@@ -248,6 +259,12 @@ static void uart_isr(struct rt_serial_device *serial)
     /* UART in mode Receiver -------------------------------------------------*/
     rt_hw_serial_isr(serial, RT_SERIAL_EVENT_RX_IND);
 
+    /* Clear error flags: an uncleared overrun (OR) inhibits all further
+     * reception on LPUART, permanently wedging RX. */
+    LPUART_ClearStatusFlags(uart->uart_base,
+                            kLPUART_RxOverrunFlag | kLPUART_FramingErrorFlag |
+                            kLPUART_NoiseErrorFlag | kLPUART_ParityErrorFlag);
+
     /* leave interrupt */
     rt_interrupt_leave();
 }

bsp/nxp/mcx/mcxn/frdm-mcxn947/board/SConscript

@@ -24,7 +24,7 @@ if GetDepend(['PKG_USING_CJSON']) and GetDepend(['PKG_USING_WEBCLIENT']):
 
 
 CPPPATH = [cwd, cwd + '/MCUX_Config/board']
-CPPDEFINES = ['DEBUG', 'CPU_MCXN947VDF_cm33_core0']
+CPPDEFINES = ['DEBUG', 'CPU_MCXN947VDF_cm33_core0', 'LPFLEXCOMM_INIT_NOT_USED_IN_DRIVER=1']
 
 group = DefineGroup('Drivers', src, depend = [''], CPPPATH = CPPPATH, CPPDEFINES=CPPDEFINES)
 

bsp/nxp/mcx/mcxn/frdm-mcxn947/board/board.c

@@ -18,6 +18,7 @@
 #include "drv_uart.h"
 #include "fsl_port.h"
 #include "fsl_cache_lpcac.h"
+#include "fsl_lpflexcomm.h"
 
 /**
  * This is the timer interrupt service routine.
@@ -34,13 +35,55 @@ void SysTick_Handler(void)
     rt_interrupt_leave();
 }
 
+/* One-time LP_FLEXCOMM function selection (upstream PR #11186). With
+ * LPFLEXCOMM_INIT_NOT_USED_IN_DRIVER=1 the fsl drivers no longer re-run
+ * LP_FLEXCOMM_Init on every configure (which reset the peripheral and
+ * killed console RX), so the mode must be selected once here. */
+static void rt_hw_flexcomm_mode_init(void)
+{
+    /* One entry per FLEXCOMM instance, covering every peripheral the
+     * drv_uart/drv_i2c/drv_spi drivers can enable on it. Instances that
+     * support several functions are mutually exclusive per Kconfig,
+     * except FC2 whose LPI2CAndLPUART mode serves both users at once
+     * (this board routes FC2 I2C on P0/P1 and UART on P2/P3). */
+#ifdef BSP_USING_I2C0
+    LP_FLEXCOMM_Init(0, LP_FLEXCOMM_PERIPH_LPI2C);
+#endif
+#if defined(BSP_USING_SPI1)
+    LP_FLEXCOMM_Init(1, LP_FLEXCOMM_PERIPH_LPSPI);
+#elif defined(BSP_USING_I2C1)
+    LP_FLEXCOMM_Init(1, LP_FLEXCOMM_PERIPH_LPI2C);
+#endif
+#if defined(BSP_USING_UART2) || defined(BSP_USING_I2C2)
+    LP_FLEXCOMM_Init(2, LP_FLEXCOMM_PERIPH_LPI2CAndLPUART);
+#endif
+#ifdef BSP_USING_SPI3
+    LP_FLEXCOMM_Init(3, LP_FLEXCOMM_PERIPH_LPSPI);
+#endif
+#ifdef BSP_USING_UART4
+    LP_FLEXCOMM_Init(4, LP_FLEXCOMM_PERIPH_LPUART);
+#endif
+#ifdef BSP_USING_UART5
+    LP_FLEXCOMM_Init(5, LP_FLEXCOMM_PERIPH_LPUART);
+#endif
+#if defined(BSP_USING_UART6)
+    LP_FLEXCOMM_Init(6, LP_FLEXCOMM_PERIPH_LPUART);
+#elif defined(BSP_USING_SPI6)
+    LP_FLEXCOMM_Init(6, LP_FLEXCOMM_PERIPH_LPSPI);
+#endif
+#ifdef BSP_USING_SPI7
+    LP_FLEXCOMM_Init(7, LP_FLEXCOMM_PERIPH_LPSPI);
+#endif
+}
+
 /**
  * This function will initial board.
  */
 void rt_hw_board_init()
 {
     /* Hardware Initialization */
     BOARD_InitBootPins();
+    rt_hw_flexcomm_mode_init();
     L1CACHE_EnableCodeCache();
 
     CLOCK_EnableClock(kCLOCK_Freqme);