ISP1160
Embedded USB Host Controller
Philips Semiconductors
Table 27: HcLSThreshold register: bit description
Bit
Symbol
−
Description
31 to 11
10 to 0
reserved
LST[10:0]
LSThreshold: Contains a value that is compared to the
FrameRemaining field before a low-speed transaction is initiated.
The transaction is started only if FrameRemaining ≥ this field. The
value is calculated by the HCD, which considers transmission and
set-up overhead.
10.3 HC Root Hub registers
All registers included in this partition are dedicated to the USB Root Hub, which is an
integral part of the HC although it is functionally a separate entity. The Host Controller
Driver (HCD) emulates USBD accesses to the Root Hub via a register interface. The
HCD maintains many USB-defined hub features that are not required to be supported
in hardware. For example, the Hub’s Device, Configuration, Interface, and Endpoint
Descriptors, as well as some static fields of the Class Descriptor, are maintained only
in the HCD. The HCD also maintains and decodes the Root Hub’s device address as
well as other minor operations more suited for software than hardware.
The Root Hub registers were developed to match the bit organization and operation
of typical hubs found in the system.
Four 32-bit registers have been defined:
• HcRhDescriptorA
• HcRhDescriptorB
• HcRhStatus
• HcRhPortStatus[1:NDP]
Each register is read and written as a DWORD. These registers are only written
during initialization to correspond with the system implementation. The
HcRhDescriptorA and HcRhDescriptorB registers are writeable regardless of the
HC’s USB states. HcRhStatus and HcRhPortStatus are writeable during the
USBOperational state only.
10.3.1 HcRhDescriptorA register (R/W: 12H/92H)
The HcRhDescriptorA register is the first register of two describing the characteristics
of the Root Hub. Reset values are implementation-specific (IS). The descriptor length
(11), descriptor type and hub controller current (0) fields of the hub Class Descriptor
are emulated by the HCD. All other fields are located in registers HcRhDescriptorA
and HcRhDescriptorB.
Remark: IS denotes an implementation-specific reset value for that field.
Code (Hex): 12 — read
Code (Hex): 92 — write
9397 750 11371
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
Product data
Rev. 04 — 04 July 2003
48 of 88
NXP [ NXP ]
