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Universal Serial Bus Interface – On-The-Go Module
Freescale Semiconductor
10-69
10.5.3.5
Managing Queue Heads
The device queue head (dQH) points to the linked list of transfer tasks, each depicted by the device transfer
descriptor (dTD). An area of memory pointed to by EPLISTADDR contains a group of all dQH's in a
sequential list (
). The even elements in the list of dQH's receive endpoints (OUT/SETUP) and
the odd elements transmit endpoints (IN/INTERRUPT). Device transfer descriptors are linked head to tail
starting at the queue head and ending at a terminate bit. After the dTD retires, it is no longer part of the
linked list from the queue head. Therefore, software is required to track all transfer descriptors because
pointers no longer exist within the queue head after the dTD is retired (see
).
Figure 10-44. Endpoint Queue Head Diagram
In addition to current and next pointers and the dTD overlay examined in
the dQH also contains the following parameters for the associated endpoint: multipler,
maximum packet length, and interrupt on setup. The next section includes demonstration of complete
initialization of the dQH including these fields.
Out
Ignore
Ignore
Receive
N/A
Drop
Packet
Ping
Ignore
Ignore
Ignore
Ignore
Ignore
Invalid
Ignore
Ignore
Ignore
Ignore
Ignore
1
Zero length packet
2
Force bit stuff error
Table 10-57. Isochronous Endpoint Bus Response Matrix (continued)
Token
Type
Stall
Not
Primed
Primed
Underflow
Overflow
Endpoint QH1 - Out
Endpoint QH0 - In
Endpoint QH0 - Out
ENDPOINTLISTADDR
Endpoint Queue Heads
(up to 32 elements)
Transfer
Buffer
Transfer Buffer
Pointer
Transfer
Buffer
Transfer
Buffer
Transfer
Buffer
Transfer Buffer
Pointer
Endpoint
Transfer
Descriptors
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...