Periodic Frame List - Freescale Semiconductor MPC8313E Family Reference Manual

16.5.1

Periodic Frame List

Figure 16-35 shows the organization of the periodic schedule. This schedule is for all periodic transfers
(isochronous and interrupt). The periodic schedule is referenced from the operational registers space using
the PERIODICLISTBASE address register and the FRINDEX register. The periodic schedule is based on
an array of pointers called the periodic frame list. The PERIODICLISTBASE address register is combined
with the FRINDEX register to produce a memory pointer into the frame list. The periodic frame list
implements a sliding window of work over time.
1024, 512, or 256
Operational
Registers
FRINDEX
PeriodicListBase
Periodic Frame
List Element
Address
The periodic frame list is a 4K-page aligned array of Frame List Link pointers. The length of the frame list
is programmable. The programmability of the periodic frame list is exported to system software through
the HCCPARAMS register. The length can be selected by system software as one of 8, 16, 32, 64, 128,
256, 512 or 1024 elements. Programming the size (that is, the number of elements) is accomplished by
system software writing the appropriate value into Frame List Size field in the USBCMD register.
Frame list link pointers direct the host controller to the first work item in the frame's periodic schedule for
the current microframe. The link pointers are aligned on DWord boundaries within the frame list.
Figure 16-36 shows the format for the frame list link pointer.
31
Frame list link pointers always reference memory objects that are 32-byte aligned. The referenced object
may be an isochronous transfer descriptor for high-speed devices, a split-transaction isochronous transfer
descriptor (for full-speed isochronous endpoints), or a queue head (used to support high-, full- and
low-speed interrupt). System software should not place non-periodic schedule items into the periodic
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
Freescale Semiconductor
Periodic Frame List
•
•
•
Elements
Figure 16-35. Periodic Schedule Organization
Frame List Link Pointer
Figure 16-36. Frame List Link Pointer Format
•
Isochronous Transfer
•
Descriptor(s)
•
A
A
A
A
• • •
A
4
A
8
A
Poll Rate: N –– > 1
Interrupt Queue
Heads
Universal Serial Bus Interface
Last
Periodic has
End of
List Mark
1
5 4 3 2 1 0
00 Typ T
16-49