fix cdcacm: need to force a valid OTG session if BOARD_USB_VBUS_SENSE…

…_DISABLED

Required for example on STM32F745 boards.

stm32/cdcacm.c

@@ -47,6 +47,13 @@
 #if INTERFACE_USB != 0
 #define USB_CDC_REQ_GET_LINE_CODING			0x21 // Not defined in libopencm3
 
+#ifndef OTG_GOTGCTL_BVALOVAL
+#define OTG_GOTGCTL_BVALOVAL   (1 << 7)
+#endif
+#ifndef OTG_GOTGCTL_BVALOEN
+#define OTG_GOTGCTL_BVALOEN    (1 << 6)
+#endif
+
 /*
  * ST changed the meaning and sense of a few critical bits
  * in the USB IP block identified as 0x00002000
@@ -316,6 +323,9 @@ usb_cinit(void)
 
 #if defined(BOARD_USB_VBUS_SENSE_DISABLED)
 	OTG_FS_GCCFG |= OTG_GCCFG_NOVBUSSENS;
+
+	/* Force valid B-peripheral session */
+	OTG_FS_GOTGCTL |= OTG_GOTGCTL_BVALOEN | OTG_GOTGCTL_BVALOVAL;
 #endif
 
 	usbd_dev = usbd_init(&otgfs_usb_driver, &dev, &config, usb_strings, NUM_USB_STRINGS,