Texas Instruments TMS320C6747 DSP manual HC Root Hub a Register Hcrhdescriptora, Potpg, Nocp

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3.19 HC Root Hub A Register (HCRHDESCRIPTORA)

The HC root hub A register (HCRHDESCRIPTORA) defines several aspects of the USB host controller root hub functionality. HCRHDESCRIPTORA is shown in Figure 20 and described in Table 20.

Figure 20. HC Root Hub A Register (HCRHDESCRIPTORA)

31						24		16
		POTPG						Reserved
		R/W-Ah						R-0
15	13	12	11	10	9	8	7	0
Reserved		NOCP	OCPM	DT	NPS	PSM		NDP
R-0		R/W-1	R/W-0	R-0	R/W-1	R/W-0		R-3h

LEGEND: R/W = Read/Write; R = Read only; -n= value after reset

Table 20. HC Root Hub A Register (HCRHDESCRIPTORA) Field Descriptions

Bit	Field	Value	Description
31-24	POTPG	0-FFh	Power-on to power-good time. Defines the minimum amount of time (2 ms × POTPG) between the USB
			host controller turning on power to a downstream port and when the USB host can access the
			downstream device. This field has no effect on USB host controller operation. After turning on power to
			a port, the USB host controller driver must delay the amount of time implied by POTPG before
			attempting to reset an attached downstream device. The required amount of time is
			implementation-specific and must be calculated based on the amount of time the VBUS supply takes to
			provide valid VBUS to a worst-case downstream USB function controller. The implementation-specific
			value must be computed and then written to this register before the USB host controller driver is
			initialized. Because the device does not provide a direct control from the USB host controller to switch
			VBUS on and off, this value must take into account any delays caused by other methods of controlling
			VBUS externally. This field has no relationship to the OTG controller register bits that relate to VBUS.
			System software can update this register to simplify host controller driver and/or OTG driver coding.
23-13	Reserved	0	Reserved
12	NOCP	1	No overcurrent protection. Because the device does not provide signals to allow connection of external
			overcurrent indication signals to the USB host controller, this bit defaults to 1 that indicates that the USB
			host controller does not implement overcurrent protection inputs. This bit has no relationship to the OTG
			controller register bits that relate to VBUS.
11	OCPM	0	Overcurrent protection mode. Because the device does not provide host controller overcurrent
			protection input signals, this bit has no effect. This bit has no relationship to the OTG controller register
			bits that relate to VBUS.
10	DT	0	Device type. This bit is always 0, which indicates that the USB host controller implemented is not a
			compound device.
9	NPS	1	No power switching. Because the device does not provide connections from the USB host controller to
			control external VBUS switching, this bit defaults to 1 that indicates that VBUS power switching is not
			supported and that power is available to all downstream ports when the USB host controller is powered.
			This bit has no relationship to the OTG controller register bits that relate to VBUS. System software can
			update this register to simplify host controller driver and/or OTG driver coding.
8	PSM	0	Power switching mode. Because the device does not provide signals from the USB host controller to
			control external VBUS switching, this bit defaults to 0 that indicates that all ports are powered at the
			same time.
7-0	NDP	0-FFh	Number of downstream ports. The USB signal multiplexing mode and top-level pin multiplexing features
			can place the device in a mode where 0, 1, 2, or 3 of the USB host controller downstream ports are
			usable. This register reports three ports, regardless of USB signal multiplexing mode and top-level pin
			multiplexing mode.

SPRUFM8–September 2008	Universal Serial Bus OHCI Host Controller	27
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