Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
24-56
Freescale Semiconductor
24.8.4.5
siTD Back Link Pointer
DWord 6 of a siTD is simply another schedule link pointer. This pointer is always zero, or references a
siTD. This pointer cannot reference any other schedule data structure.
24.8.5
Queue Element Transfer Descriptor (qTD)
This data structure is only used with a queue head. This data structure is used for one or more USB
transactions. This data structure is used to transfer up to 20480 (5
×
4096) bytes. The structure contains
two structure pointers used for queue advancement, a DWord of transfer state, and a five-element array of
data buffer pointers. This structure is 32 bytes (or one 32-byte cache line). This data structure must be
physically contiguous.
The buffer associated with this transfer must be virtually contiguous. The buffer may start on any byte
boundary. A separate buffer pointer list element must be used for each physical page in the buffer,
regardless of whether the buffer is physically contiguous.
Host controller updates (host controller writes) to stand-alone qTDs only occur during transfer retirement.
References in the following bit field definitions of updates to the qTD are to the qTD portion of a queue
head.
Table 24-49. siTD Buffer Pointer Page 1 (Plus)
Bit
Name
Description
31–12 Buffer
Pointer
(Page 1)
Bits [31–12] is a 4K page-aligned, physical memory addresses. These bits correspond to physical
address bits [31–12] respectively. The field P specifies the current active pointer
11–5 –
Reserved.
4–3
TP
Transaction position. This field is used with T-count to determine whether to send all, first, middle, or
last with each outbound transaction payload. The system software must initialize this field with the
appropriate starting value. The host controller must correctly manage this state during the lifetime of
the transfer. The bit encodings are:
00 All. The entire full-speed transaction data payload is in this transaction (that is, less than or equal
to 188 bytes).
01 Begin. This is the first data payload for a full-speed transaction that is greater than 188 bytes.
10 Mid. This is the middle payload for a full-speed OUT transaction that is larger than 188 bytes.
11 End. This is the last payload for a full-speed OUT transaction that was larger than 188 bytes.
2–0
T-Count
Transaction count. The software initializes this field with the number of OUT start-splits this transfer
requires. Any value larger than 6 is undefined.
Table 24-50. siTD Back Link Pointer
Bit
Name
Description
31–5
Back Pointer
This field is a physical memory pointer to a siTD.
4–1
–
Reserved. This field is reserved for future use. It should be cleared.
0 T
Terminate
0 siTD Back Pointer field is valid
1 siTD Back Pointer field is not valid
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...
