NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 728 -
Revision V1.30
NUC97
0
T
E
CHNIC
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L
RE
F
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RE
N
CE
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NUA
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[6]
IAAD
Interrupt on Async Advance Doorbell (R/W)
This bit is used as a doorbell by software to tell the host controller to issue an interrupt the
next time it advances asynchronous schedule. Software must write a 1 to this bit to ring
the doorbell.
When the host controller has evicted all appropriate cached schedule state, it sets the
Interrupt on Async Advance status bit in the USBSTS register. If the Interrupt on Async
Advance Enable bit in the USBINTR register is a one then the host controller will assert
an interrupt at the next interrupt threshold.
The host controller sets this bit to a zero after it has set the Interrupt on Async Advance
status bit in the USBSTS register to a one.
Software should not write a one to this bit when the asynchronous schedule is disabled.
Doing so will yield undefined results.
[5]
ASEN
Asynchronous Schedule Enable (R/W)
This bit controls whether the host controller skips processing the Asynchronous Schedule.
Values mean:
0 = Do not process the Asynchronous Schedule.
1 = Use the ASYNCLISTADDR register to access the Asynchro-nous Schedule.
[4]
PSEN
Periodic Schedule Enable (R/W)
This bit controls whether the host controller skips processing the Periodic Schedule.
Values mean:
0 = Do not process the Periodic Schedule.
1 = Use the PERIODICLISTBASE register to access the Periodic Schedule.
[3:2]
FLSZ
Frame List Size (R/W or RO)
This field is R/W only if Programmable Frame List Flag in the HCCPARAMS registers is
set to a one. This field specifies the size of the frame list. The size the frame list controls
which bits in the Frame Index Register should be used for the Frame List Current index.
Values mean:
00 = 1024 elements (4096 bytes) Default value.
01 = 512 elements (2048 bytes).
10 = 256 elements (1024 bytes)
– for resource-constrained environment.
11 = Reserved.
[1]
HCRST
Host Controller Reset (HCRESET) (R/W)
This control bit is used by software to reset the host controller. The effects of this on Root
Hub registers are similar to a Chip Hardware Reset.
When software writes a one to this bit, the Host Controller resets its internal pipelines,
timers, counters, state machines, etc. to their initial value. Any transaction currently in
progress on USB is immediately terminated. A USB reset is not driven on downstream
ports.
All operational registers, including port registers and port state machines are set to their
initial values. Port ownership reverts to the companion host controller(s), with the side
effects. Software must reinitialize the host controller in order to return the host controller to
an operational state.
This bit is set to zero by the Host Controller when the reset process is complete. Software
cannot terminate the reset process early by writing a zero to this register.
Software should not set this bit to a one when the HCHalted bit in the USBSTS register is
a zero. Attempting to reset an actively running host controller will result in undefined
behavior.