USB Clock Status
| RESERVED | Reserved. Read value is undefined, only zero should be written. |
| DEV_CLK_ON | Device clock on. The usbclk input to the device controller is active . |
| RESERVED | Reserved. Read value is undefined, only zero should be written. |
| PORTSEL_CLK_ON | Port select register clock on. |
| AHB_CLK_ON | AHB clock on. |
| RESERVED | Reserved. The value read from a reserved bit is not defined. |