MPC8536-RDK Freescale Semiconductor, MPC8536-RDK Datasheet - Page 1472

Manufacturer Part Number

BOARD REF COMEXPRESS MPC8536

Manufacturer

Freescale Semiconductor

PowerQUICC ™r

CSB1880, CSB1801, Cables, Documentation, Enclosure, Power Supply with cord

For Use With/related Products

Lead Free Status / RoHS Status

Lead free / RoHS Compliant

Universal Serial Bus Interfaces

It is necessary for the DCD software to maintain head and tail pointers to the 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 to be executed. The operations described in next section for managing dTD

will assume the DCD can use reference the head and tail of the dTD linked list.

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 8-DWord dTD block of memory aligned to 8-DWord boundaries. Example: bit address 4–0 would

be equal to ‘00000’

Write the following fields:

4. Decode setup packet and prepare data phase [optional] and status phase transfer as required by the

1. Initialize first 7 DWords to 0.

2. Set the terminate bit to ‘1.’

3. Fill in total bytes with transfer size.

4. Set the interrupt on complete if desired.

5. Initialize the status field with the active bit set to ‘1’ and all remaining status bits set to ‘0.’

USB Chapter 9 or application specific protocol.

Managing Transfers with Transfer Descriptors

Software Link Pointers

Building a Transfer Descriptor

It is possible for the device controller to receive setup packets before

previous control transfers complete. Existing control packets in progress

must be flushed and the new control packet completed.

To conserve memory, the reserved fields at the end of the dQH can be used

to store the Head and Tail pointers but it still remains the responsibility of

the DCD to maintain the pointers.

Head Pointer

MPC8536E PowerQUICC III Integrated Processor Reference Manual, Rev. 1

Completed dTDs

Figure 21-64. Software Link Pointers

Tail Pointer

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