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Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
24-151
24.12.1.5.3
Asynchronous Transaction Scheduling and Buffer Management
The following USB 2.0 specification items are implemented in the embedded Transaction Translator:
•
USB 2.0 – 11.17.3
— Sequencing is provided and a packet length estimator ensures no full-speed/low-speed packet
babbles into SOF time.
•
USB 2.0 – 11.17.4
— • Transaction tracking for 2 data pipes.
•
USB 2.0 – 11.17.5
— • Clear_TT_Buffer capability provided though the use of the Error! Reference source not
found. register.
24.12.1.5.4
Periodic Transaction Scheduling and Buffer Management
The following USB 2.0 specification items are implemented in the embedded Transaction Translator:
•
USB 2.0 – 11.18.6.[1-2]
— Abort of pending start-splits
– EOF (and not started in microframes 6)
– Idle for more than 4 microframes
— Abort of pending complete-splits
– EOF
– Idle for more than 4 microframes
•
USB 2.0
—
11.18.[7-8]
— Transaction tracking for up to 16 data pipes.
– Some applications may not require transaction tracking up to a maximum of 16 periodic data
pipes. The option to limit the tracking to only 4 periodic data pipes exists in the by changing
the configuration constant VUSB_HS_TT_PERIODIC_CONTEXTS to 4. The result is a
significant gate count savings to the core given the limitations implied.
Table 24-94. Emulated Handshakes
Condition
Emulate TT Response
Start-Split: All asynchronous buffers full.
NAK
Start-Split: All periodic buffers full.
ERR
Start-Split: Success for start of Async. Transaction.
ACK
Start-Split: Start Periodic Transaction.
No Handshake (Ok)
Complete-Split: Failed to find transaction in queue.
Bus Time Out
Complete-Split: Transaction in Queue is Busy.
NYET
Complete-Split: Transaction in Queue is Complete.
[Actual Handshake from FS/LS device]
Содержание MCF5253
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