Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
24-93
Figure 24-54. General Structure of EHCI Periodic Schedule Utilizing Interrupt Spreading
The periodic frame list is effectively the leaf level a binary tree, which is always traversed leaf to root.
Each level in the tree corresponds to a 2
N
poll rate. The software can efficiently manage periodic
bandwidth on the USB by spreading interrupt queue heads that have the same poll rate requirement across
all the available paths from the frame list. For example, system the software can schedule eight poll rate 8
queue heads and account for them once in the high-speed bus bandwidth allocation.
When an endpoint is allocated an execution footprint that spans a frame boundary, the queue head for the
endpoint must be reachable from consecutive locations in the frame list. An example would be if 8
0b
were
such an endpoint. Without additional support on the interface, to get 8
0b
reachable at the correct time, the
software would have to link 8
1
to 8
0b
. It would then have to move 4
1
and everything linked after into the
same path as 4
0
. This upsets the integrity of the binary tree and disallows the use of the spreading
technique.
FSTN data structures are used to preserve the integrity of the binary-tree structure and enable the use of
the spreading technique.
Section 24.8.7, “Periodic Frame Span Traversal Node (FSTN),”
defines the
hardware and software operational model requirements for using FSTNs.
The following queue head fields are initialized by the system software to instruct the host controller when
to execute portions of the split-transaction protocol.
•
SplitXState. This is a single bit residing in the Status field of a queue head (
is used to track the current state of the split transaction.
•
Frame S-mask. This is a bit-field where the system software sets a bit corresponding to the
micro-frame (within an H-Frame) that the host controller should execute a start-split transaction.
This is always qualified by the value of the SplitXState bit in the Status field of the queue head.
For example, referring to
, case one, the S-mask would have a value of 0b0000_0001
indicating that if the queue head is traversed by the host controller, and the SplitXState indicates
Do_Start, and the current micro-frame as indicated by FRINDEX[2:0] is 0, then execute a
start-split transaction.
2
1
4
3
•
•
•
4
0
2
0
1
0
Periodic
Frame List
• • •
8
7
8
6
8
5
8
4
8
3
8
2
8
1
8
0
8
0b
4
2
4
1
Level 8
Level 4
Level 2
Level 1
Linkage repeats every 8 for
remainder of frame list
(Root)
Summary of Contents for MCF5253
Page 1: ...Document Number MCF5253RM Rev 1 08 2008 MCF5253 Reference Manual...
Page 26: ...MCF5253 Reference Manual Rev 1 xxvi Freescale Semiconductor...
Page 32: ...MCF5253 Reference Manual Rev 1 xxxii Freescale Semiconductor...
Page 46: ...MCF5253 Introduction MCF5253 Reference Manual Rev 1 1 14 Freescale Semiconductor...
Page 62: ...Signal Description MCF5253 Reference Manual Rev 1 2 16 Freescale Semiconductor...
Page 98: ...Instruction Cache MCF5253 Reference Manual Rev 1 5 10 Freescale Semiconductor...
Page 104: ...Static RAM SRAM MCF5253 Reference Manual Rev 1 6 6 Freescale Semiconductor...
Page 128: ...Synchronous DRAM Controller Module MCF5253 Reference Manual Rev 1 7 24 Freescale Semiconductor...
Page 144: ...Bus Operation MCF5253 Reference Manual Rev 1 8 16 Freescale Semiconductor...
Page 176: ...System Integration Module SIM MCF5253 Reference Manual Rev 1 9 32 Freescale Semiconductor...
Page 198: ...Analog to Digital Converter ADC MCF5253 Reference Manual Rev 1 12 6 Freescale Semiconductor...
Page 246: ...DMA Controller MCF5253 Reference Manual Rev 1 14 18 Freescale Semiconductor...
Page 282: ...UART Modules MCF5253 Reference Manual Rev 1 15 36 Freescale Semiconductor...
Page 344: ...Audio Interface Module AIM MCF5253 Reference Manual Rev 1 17 46 Freescale Semiconductor...
Page 362: ...I2 C Modules MCF5253 Reference Manual Rev 1 18 18 Freescale Semiconductor...
Page 370: ...Boot ROM MCF5253 Reference Manual Rev 1 19 8 Freescale Semiconductor...
