Information

Universal Serial Bus Interface
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 13-93
and queue head data structure. The S and C
n
labels indicate microframes where software can schedule
start-splits and complete splits (respectively).
Figure 13-53. Split Transaction, Interrupt Scheduling Boundary Conditions
The scheduling cases are:
• Case 1: The normal scheduling case is where the entire split transaction is completely bounded by
a frame (H-Frame in this case).
• Case 2a through Case 2c: The USB 2.0 hub pipeline rules states clearly, when and how many
complete-splits must be scheduled to account for earliest to latest execution on the full/low-speed
link. The complete-splits may span the H-Frame boundary when the start-split is in microframe 4
or later. When this occurs, the H-Frame to B-Frame alignment requires that the queue head be
reachable from consecutive periodic frame list locations. System software cannot build an efficient
schedule that satisfies this requirement unless it uses FSTNs. Figure 13-54 illustrates the general
layout of the periodic schedule.
7
C2C1C0S
076543210
Periodic Schedule
Micro-Frame
1
Case 1:
Normal Case
C1C0S
Case 2a:
End of Frame
C2C1C0S
C2C1C0S
6765432107
HS/FS/LS Bus
Micro-Frame
0
Case 2b:
End of Frame
Case 2c:
End of Frame
B-Frame N B-Frame N+1B-Frame N–1
H-Frame N