Functional Description
Debug Software Startup with Non-Initialized EHCI
Debug software can attempt to use the debug port if after setting the OWNER_CNT bit,
the Current Connect Status bit in the appropriate (See Determining the Debug Port)
PORTSC register is set. If the Current Connect Status bit is not set, then debug
software may choose to terminate or it may choose to wait until a device is connected.
If a device is connected to the port, then debug software must reset/enable the port.
Debug software does this by setting and then clearing the Port Reset bit the PORTSC
register. To ensure a successful reset, debug software should wait at least 50 ms before
clearing the Port Reset bit. Due to possible delays, this bit may not change to 0
immediately; reset is complete when this bit reads as 0. Software must not continue
until this bit reads 0.
If a high-speed device is attached, the EHCI will automatically set the Port Enabled/
Disabled bit in the PORTSC register and the debug software can proceed. Debug
software should set the ENABLED_CNT bit in the Debug Port Control/Status register,
and then reset (clear) the Port Enabled/Disabled bit in the PORTSC register (so that the
system host controller driver does not see an enabled port when it is first loaded).
Debug Software Startup with Initialized EHCI
Debug software can attempt to use the debug port if the Current Connect Status bit in
the appropriate (See Determining the Debug Port) PORTSC register is set. If the
Current Connect Status bit is not set, then debug software may choose to terminate or
it may choose to wait until a device is connected.
If a device is connected, then debug software must set the OWNER_CNT bit and then
the ENABLED_CNT bit in the Debug Port Control/Status register.
Determining Debug Peripheral Presence
After enabling the debug port functionality, debug software can determine if a debug
peripheral is attached by attempting to send data to the debug peripheral. If all
attempts result in an error (Exception bits in the Debug Port Control/Status register
indicates a Transaction Error), then the attached device is not a debug peripheral. If the
debug port peripheral is not present, then debug software may choose to terminate or
it may choose to wait until a debug peripheral is connected.
5.19.11 USB Pre-Fetch Based Pause
The Pre-Fetch Based Pause is a power management feature in USB (EHCI) host
controllers to ensure maximum C3/C4 processor power state time with C2 popup. This
feature applies to the period schedule, and works by allowing the DMA engine to
identify periods of idleness and preventing the DMA engine from accessing memory
when the periodic schedule is idle. Typically in the presence of periodic devices with
multiple millisecond poll periods, the periodic schedule will be idle for several frames
between polls.
The USB Pre-Fetch Based Pause feature is disabled by setting bit 4 of EHCI
Configuration Register Section 17.1.30.
Datasheet
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INTEL [ INTEL ]
