stm32/uart: Add support for UART4/5 on L0 MCUs.

ports/stm32/mpconfigboard_common.h

@@ -196,7 +196,7 @@
 #define PYB_EXTI_NUM_VECTORS (30) // TODO (22 configurable, 7 direct)
 #define MICROPY_HW_MAX_I2C (3)
 #define MICROPY_HW_MAX_TIMER (22)
-#define MICROPY_HW_MAX_UART (4)
+#define MICROPY_HW_MAX_UART (5)
 
 // Configuration for STM32L4 series
 #elif defined(STM32L4)

ports/stm32/stm32_it.c

@@ -731,6 +731,15 @@ void USART3_8_IRQHandler(void) {
     IRQ_EXIT(USART3_8_IRQn);
 }
 
+#elif defined(STM32L0)
+
+void USART4_5_IRQHandler(void) {
+    IRQ_ENTER(USART4_5_IRQn);
+    uart_irq_handler(4);
+    uart_irq_handler(5);
+    IRQ_EXIT(USART4_5_IRQn);
+}
+
 #else
 
 void USART3_IRQHandler(void) {

ports/stm32/uart.c

@@ -247,6 +247,10 @@ bool uart_init(pyb_uart_obj_t *uart_obj,
             UARTx = USART4;
             irqn = USART3_8_IRQn;
             __HAL_RCC_USART4_CLK_ENABLE();
+            #elif defined(STM32L0)
+            UARTx = USART4;
+            irqn = USART4_5_IRQn;
+            __HAL_RCC_USART4_CLK_ENABLE();
             #else
             UARTx = UART4;
             irqn = UART4_IRQn;
@@ -274,6 +278,10 @@ bool uart_init(pyb_uart_obj_t *uart_obj,
             UARTx = USART5;
             irqn = USART3_8_IRQn;
             __HAL_RCC_USART5_CLK_ENABLE();
+            #elif defined(STM32L0)
+            UARTx = USART5;
+            irqn = USART4_5_IRQn;
+            __HAL_RCC_USART5_CLK_ENABLE();
             #else
             UARTx = UART5;
             irqn = UART5_IRQn;