stmhal: L4: Modify uart.c to support L4 MCU.

L4 does not have UART6, and has similar registers to the F7.

Original patch was authored by Tobias Badertscher / @tobbad, but it was
reworked to split UART edits from USB edits.

stmhal/uart.c

@@ -150,7 +150,6 @@ STATIC bool uart_init2(pyb_uart_obj_t *uart_obj) {
         #endif
 
         #if defined(MICROPY_HW_UART2_PORT) && defined(MICROPY_HW_UART2_PINS)
-        // USART2 is on PA2/PA3 (CTS,RTS,CK on PA0,PA1,PA4), PD5/PD6 (CK on PD7)
         case PYB_UART_2:
             UARTx = USART2;
             irqn = USART2_IRQn;
@@ -327,7 +326,7 @@ int uart_rx_char(pyb_uart_obj_t *self) {
         return data;
     } else {
         // no buffering
-        #if defined(MCU_SERIES_F7)
+        #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
         return self->uart.Instance->RDR & self->char_mask;
         #else
         return self->uart.Instance->DR & self->char_mask;
@@ -398,7 +397,7 @@ void uart_irq_handler(mp_uint_t uart_id) {
             uint16_t next_head = (self->read_buf_head + 1) % self->read_buf_len;
             if (next_head != self->read_buf_tail) {
                 // only read data if room in buf
-                #if defined(MCU_SERIES_F7)
+                #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
                 int data = self->uart.Instance->RDR; // clears UART_FLAG_RXNE
                 #else
                 int data = self->uart.Instance->DR; // clears UART_FLAG_RXNE
@@ -571,12 +570,20 @@ STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, mp_uint_t n_args, con
     // compute actual baudrate that was configured
     // (this formula assumes UART_OVERSAMPLING_16)
     uint32_t actual_baudrate;
-    if (self->uart.Instance == USART1 || self->uart.Instance == USART6) {
+    if (self->uart.Instance == USART1
+        #if defined(USART6)
+        || self->uart.Instance == USART6
+        #endif
+        ) {
         actual_baudrate = HAL_RCC_GetPCLK2Freq();
     } else {
         actual_baudrate = HAL_RCC_GetPCLK1Freq();
     }
+    #if defined(MCU_SERIES_L4)
+    actual_baudrate = (actual_baudrate << 5) / (self->uart.Instance->BRR >> 3);
+    #else
     actual_baudrate /= self->uart.Instance->BRR;
+    #endif
 
     // check we could set the baudrate within 5%
     uint32_t baudrate_diff;
@@ -716,11 +723,13 @@ STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in) {
         __UART5_RELEASE_RESET();
         __UART5_CLK_DISABLE();
     #endif
+    #if defined(UART6)
     } else if (uart->Instance == USART6) {
         HAL_NVIC_DisableIRQ(USART6_IRQn);
         __USART6_FORCE_RESET();
         __USART6_RELEASE_RESET();
         __USART6_CLK_DISABLE();
+    #endif
     }
     return mp_const_none;
 }
@@ -776,7 +785,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_readchar_obj, pyb_uart_readchar);
 // uart.sendbreak()
 STATIC mp_obj_t pyb_uart_sendbreak(mp_obj_t self_in) {
     pyb_uart_obj_t *self = self_in;
-    #if defined(MCU_SERIES_F7)
+    #if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
     self->uart.Instance->RQR = USART_RQR_SBKRQ; // write-only register
     #else
     self->uart.Instance->CR1 |= USART_CR1_SBK;