Use USB clock recovery when running USB from IRC48M oscillator

teensy3/kinetis.h

@@ -3882,6 +3882,17 @@ typedef struct {
 #define USB_USBTRC_SYNC_DET		((uint8_t)0x02)			//
 #define USB_USBTRC_USB_RESUME_INT	((uint8_t)0x01)			//
 #define USB0_USBFRMADJUST	(*(volatile uint8_t  *)0x40072114) // Frame Adjust Register
+#define USB0_CLK_RECOVER_CTRL	(*(volatile uint8_t  *)0x40072140) // USB Clock recovery control
+#define USB_CLK_RECOVER_CTRL_CLOCK_RECOVER_EN		((uint8_t)0x80)
+#define USB_CLK_RECOVER_CTRL_RESET_RESUME_ROUGH_EN	((uint8_t)0x40)
+#define USB_CLK_RECOVER_CTRL_RESTART_IFRTRIM_EN		((uint8_t)0x20)
+#define USB0_CLK_RECOVER_IRC_EN	(*(volatile uint8_t  *)0x40072144) // IRC48M oscillator enable 
+#define USB_CLK_RECOVER_IRC_EN_IRC_EN			((uint8_t)0x02)
+#define USB_CLK_RECOVER_IRC_EN_REG_EN			((uint8_t)0x01)
+#define USB0_CLK_RECOVER_INT_EN	(*(volatile uint8_t  *)0x40072154) // Clock recovery combined interrupt enable
+#define USB_CLK_RECOVER_INT_EN_OVF_ERROR_EN		((uint8_t)0x10)
+#define USB0_CLK_RECOVER_INT_STATUS (*(volatile uint8_t  *)0x4007215C) // Clock recovery separated interrupt status
+#define USB_CLK_RECOVER_INT_STATUS_OVF_ERROR		((uint8_t)0x10)
 
 
 // USB Device Charger Detection Module (USBDCD)

teensy3/usb_dev.c

@@ -1111,7 +1111,12 @@ void usb_init(void)
 #ifdef HAS_KINETIS_MPU
 	MPU_RGDAAC0 |= 0x03000000;
 #endif
-
+#if F_CPU == 180000000 || F_CPU == 216000000
+	// if using IRC48M, turn on the USB clock recovery hardware
+	USB0_CLK_RECOVER_IRC_EN = USB_CLK_RECOVER_IRC_EN_IRC_EN | USB_CLK_RECOVER_IRC_EN_REG_EN;
+	USB0_CLK_RECOVER_CTRL = USB_CLK_RECOVER_CTRL_CLOCK_RECOVER_EN |
+		USB_CLK_RECOVER_CTRL_RESTART_IFRTRIM_EN;
+#endif
 	// reset USB module
 	//USB0_USBTRC0 = USB_USBTRC_USBRESET;
 	//while ((USB0_USBTRC0 & USB_USBTRC_USBRESET) != 0) ; // wait for reset to end