Freescale Semiconductor MPC8313E Family Reference Manual page 1040

Universal Serial Bus Interface
IN or an OUT). Refer to the EHCI Specification for a complete list of additional conditions that
must be met in general for the host controller to issue a bus transaction. Note that the host controller
must not execute a Start-split transaction while executing in Recovery Path mode. Refer to the
EHCI Specification for special handling when in Recovery Path mode.
• Stop traversing the recovery path when it encounters an FSTN that is a Restore indicator. The host
controller unconditionally uses the saved value of the Save-Place FSTN's Normal Path Link
Pointer when returning to the normal path traversal. The host controller must clear the context of
executing a Recovery Path when it restores schedule traversal to the Save-Place FSTN's Normal
Path Link Pointer.
If the host controller determines that there is not enough time left in the microframe to complete
processing of the periodic schedule, it abandons traversal of the recovery path, and clears the
context of executing a recovery path. The result is that at the start of the next consecutive
microframe, the host controller starts traversal at the frame list.
An example traversal of a periodic schedule that includes FSTNs is illustrated in
Frame Numbers
N+5
N+4
N+3
Normal Traversal
for Frame N+1
Micro-Frames 0, 1
N+1
Normal Traversal
for Frame N
N
N–1
N–2
Figure 16-55. Example Host Controller Traversal of Recovery Path via FSTNs
In frame N (microframes 0-7), for this example, the host controller traverses all of the schedule data
structures utilizing the Normal Path Link Pointers in any FSTNs it encounters. This is because the host
controller has not yet encountered a Save-Place FSTN so it is not executing in Recovery Path mode. When
it encounters the Restore FSTN, (Restore-N), during microframes 0 and 1, it uses Restore-N. Normal Path
Link Pointer to traverse to the next data structure (that is, normal schedule traversal). This is because the
host controller must use a Restore FSTN's Normal Path Link Pointer when not executing in a
Recovery-Path mode. The nodes traversed during frame N include: {8
1 ...}.
0
In frame N+1 (microframes 0 and 1), when the host controller encounters Save-Path FSTN (Save-N), it
observes that Save-N.Back Path Link Pointer.T-bit is zero (definition of a Save-Path indicator). The host
controller saves the value of Save-N. Normal Path Link Pointer and follows Save-N.Back Path Link
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
16-98
8
7
8
6
8
5
8
4
Save = N
N-Ptr
8 8 8
B-Ptr
3.0 3.1 3.2
T-Int = 0
8 8 8 8
2.0 2.1 2.2 2.3
8
1
8
0
Figure 16-55.
4
3
Causes 'Restore'
to Normal Path
Traversal
Restore = N
4 2
2 1
N-Ptr
B-Ptr
4
2
1
0
4
Recovery Path
0
Traversal
, 8 , 8 , 8 , 4
2.0 2.1 2.2 2.3 2
Freescale Semiconductor
1
0
• • •
T-Int = 1
, 2 , Restore-N,
0