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Universal Serial Bus Interface – On-The-Go Module
Freescale Semiconductor
10-19
14
ATDTW
Add dTD TripWire. This is a non-EHCI bit. This bit is used as a semaphore when a dTD is added to an active
(primed) endpoint. This bit is set and cleared by software. This bit is also cleared by hardware when the state
machine is in a hazard region where adding a dTD to a primed endpoint may go unrecognized. More
information appears in
Section 10.5.3.6.3, “Executing a Transfer Descriptor.”
13
SUTW
Setup TripWire. A non-EHCI bit. Used as a semaphore to ensure that the setup data payload of 8 bytes is
extracted from a QH by driver software without being corrupted. If the setup lockout mode is off
(USBMODE[SLOM] = 1) then a hazard exists when new setup data arrives, and the software copies setup from
the QH for a previous setup packet. This bit is set and cleared by software and is cleared by hardware when a
hazard exists. More information appears in
Section 10.5.3.4.4, “Control Endpoint Operation.”
12
Reserved, must be cleared.
11
ASPE
Asynchronous schedule park mode enable. Software uses this bit to enable or disable park mode.
1 Park mode enabled
0 Park mode disabled
10
Reserved, must be cleared.
9–8
ASP
Asynchronous schedule park mode count. Contains a count of the successive transactions the host controller
can execute from a high-speed queue head on the asynchronous schedule before continuing traversal of the
asynchronous schedule. Valid values are 0x1 to 0x3. Software must not write a zero to this field when ASPE is
set as this results in undefined behavior.
7
Reserved, must be cleared.
6
IAA
Interrupt on async advance doorbell. Used as a doorbell by software to tell controller to issue an interrupt the
next time it advances the asynchronous schedule. Software must write a 1 to this bit to ring the doorbell.
When controller has evicted all appropriate cached schedule states, it sets USBSTS[AAI] register. If the
USBINTR[AAE] bit is set, the host controller asserts an interrupt at the next interrupt threshold.
The controller clears this bit after it has set the USBSTS[AAI] bit. Software must not write a 1 to this bit when
the asynchronous schedule is inactive. Doing so yields undefined results. This bit used only in host mode.
Writing a 1 to this bit when the USB OTG module is in device mode has undefined results.
5
ASE
Asynchronous schedule enable. Controls whether the controller skips processing the asynchronous schedule.
Only used in host mode.
1 Use the ASYNCLISTADDR register to access asynchronous schedule.
0 Do not process asynchronous schedule.
4
PSE
Periodic schedule enable. Controls whether the controller skips processing periodic schedule. Used only in host
mode.
1 Use the PERIODICLISTBASE register to access the periodic schedule.
0 Do not process periodic schedule.
3–2
FS
Frame list size. With bit 15, these bits make the FS[2:0] fields, which specifies the frame list size controlling
which bits in the frame index register must be used for the frame list current index. Used only in host mode.
Note:
Values below 256 elements are not defined in the EHCI specification.
000 1024 elements (4096 bytes)
001 512 elements (2048 bytes)
010 256 elements (1024 bytes)
011 128 elements (512 bytes)
100 64 elements (256 bytes)
101 32 elements (128 bytes)
110 16 elements (64 bytes)
111 8 elements (32 bytes)
Table 10-19. USBCMD Field Descriptions (continued)
Field
Description
Содержание MCF54455
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