
Universal Serial Bus Interface – On-The-Go Module
Freescale Semiconductor
21-69
21.5.3.6
Managing Transfers with Transfer Descriptors
21.5.3.6.1
Software Link Pointers
It is necessary for the DCD software to maintain head and tail pointers for the linked list of dTDs for each
respective queue head. This is necessary because the dQH only maintains pointers to the current working
dTD and the next dTD executed. The operations described in the next section for managing dTDs assumes
DCD can reference the head and tail of the dTD linked list.
NOTE
To conserve memory, the reserved fields at the end of the dQH can be used
to store the head and tail pointers, but DCD must continue maintaining the
pointers.
Figure 21-43. Software Link Pointers
NOTE
Check the status of each dTD to determine completed status.
21.5.3.6.2
Building a Transfer Descriptor
Before a transfer can be executed from the linked list, a dTD must be built to describe the transfer. Use the
following procedure for building dTDs.
Allocate an 8-longword dTD block of memory aligned to 8-longword boundaries. The last 5 bits of the
address must equal 00000.
Write the following fields:
1. Initialize the first 7 longwords to 0.
2. Set the terminate bit.
3. Fill in total bytes with transfer size.
4. Set the interrupt on complete bit if desired.
5. Initialize the status field with the active bit set, and all remaining status bits cleared.
6. Fill in buffer pointer page 0 and the current offset to point to the start of the data buffer.
7. Initialize buffer pointer page 1 through page 4 to be one greater than each of the previous buffer
pointers.
Endpoint QH
current
next
Tail Pointer
Head Pointer
Queued dTDs
Completed dTDs
MCF5329 Reference Manual, Rev 3
Содержание MCF5329
Страница 106: ...ColdFire Core 3 32 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 126: ...Enhanced Multiply Accumulate Unit EMAC 4 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 148: ...Cache 5 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 154: ...Static RAM SRAM 6 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 184: ...Power Management 8 18 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 204: ...Reset Controller Module 10 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 220: ...System Control Module SCM 11 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 228: ...Crossbar Switch XBS 12 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 268: ...General Purpose I O Module 13 40 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 392: ...SDRAM Controller SDRAMC 18 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 436: ...Fast Ethernet Controller FEC 19 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 564: ...Liquid Crystal Display Controller LCDC 22 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 594: ...FlexCAN 23 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 678: ...Pulse Width Modulation PWM Module 26 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 684: ...Watchdog Timer Module 27 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 692: ...Programmable Interrupt Timers PIT0 PIT3 28 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 704: ...DMA Timers DTIM0 DTIM3 29 12 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 720: ...Queued Serial Peripheral Interface QSPI 30 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 754: ...UART Modules 31 34 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 770: ...I2 C Interface 32 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 790: ...Message Digest Hardware Accelerator MDHA 33 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 866: ...Debug Module 36 50 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 902: ...Register Memory Map Quick Reference A 26 Freescale Semiconductor MCF5329 Reference Manual Rev 3...