stm32h7: restore 1200bps functionality by enabling Backup area access

Author: facchinm

cores/arduino/USB.cpp

@@ -56,6 +56,7 @@ void arduino::SerialUSB_::usbd_next_cb(struct usbd_context *const ctx, const str
     if (msg->type == USBD_MSG_CDC_ACM_LINE_CODING) {
         uint32_t baudrate;
         uart_line_ctrl_get(Serial.uart, UART_LINE_CTRL_BAUD_RATE, &baudrate);
+        printf("Baud rate changed to %d\n", baudrate);
         Serial._baudChangeHandler(nullptr, baudrate);
     }
 }

loader/fixups.c

@@ -39,6 +39,16 @@ SYS_INIT(disable_bootloader_mpu, PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEFAU
 SYS_INIT(disable_mpu_rasr_xn, PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
 #endif
 
+#if defined(CONFIG_SOC_STM32H747XX_M7)
+void enable_bkp_access(void)
+{
+	/* Enable access to the backup domain */
+	// HAL_PWR_EnableBkUpAccess();
+	SET_BIT(PWR->CR1, PWR_CR1_DBP);
+}
+SYS_INIT(enable_bkp_access, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
+#endif
+
 #if defined(CONFIG_BOARD_ARDUINO_GIGA_R1) && defined(CONFIG_VIDEO)
 #include <zephyr/kernel.h>
 #include <zephyr/device.h>

variants/arduino_giga_r1_stm32h747xx_m7/arduino_giga_r1_stm32h747xx_m7.conf

@@ -67,3 +67,5 @@ CONFIG_CYW4343W_MURATA_1DX=y
 CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
 CONFIG_BT_RX_STACK_SIZE=4096
 CONFIG_BT_HCI_TX_STACK_SIZE=4096
+
+CONFIG_RTC=y

variants/arduino_giga_r1_stm32h747xx_m7/arduino_giga_r1_stm32h747xx_m7.overlay

@@ -333,6 +333,11 @@
 	};
 };
 
+&rtc {
+	clocks = <&rcc STM32_CLOCK_BUS_APB4 0x00010000>,
+		 <&rcc STM32_SRC_LSE RTC_SEL(1)>;
+	status = "okay";
+};
 
 &flash0 {
 	partitions {