Freescale Semiconductor MCF52277 Reference Manual page 434

Universal Serial Bus Interface – On-The-Go Module
Split State Machines
The start and complete-split operational model differs from EHCI slightly because there is no bus medium
between the EHCI controller and the embedded transaction translator. Where a start or complete-split
operation would occur by requesting the split to the HS hub, the start/complete-split operation is simple
an internal operation to the embedded transaction translator.
handshakes are emulated from internal state instead of actual handshakes to HS split bus traffic.
Start-Split: All asynchronous buffers full
Start-Split: All periodic buffers full
Start-Split: Success for start of async. transaction
Start-Split: Start periodic transaction
Complete-Split: Failed to find transaction in queue
Complete-Split: Transaction in queue is busy
Complete-Split: Transaction in queue is complete
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-/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 TTCTRL register.
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 4 data pipes.
20-76
Table 20-63. Emulated Handshakes
Condition
MCF52277 Reference Manual, Rev. 1
Table 20-63 summarizes the conditions where
Emulate TT Response
NAK
ERR
ACK
No handshake (Ok)
Bus time-out
NYET
Actual handshake from FS/LS device
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