Endpoint Descriptors

31

26

16

15 14 13 12 11 10

7

6

0

--------

MPS

F

K

S

D

EN

DW 0

31

Transfer Descriptor QueueailT Pointer (TailP)

DW 1

31

DW 2

Transfer Descriptor Queue HeadointerP (HeadP)

0

C

H

31

DW 3

Next Endpoint Descriptor (NextED)

Table D-1: Definition of Endpoint Descriptor Fields (DW0)

Bit

Field Name

Description

6:0

Device Address — USB device containing the target endpoint.

10:7

Bit

Field Name

Description

12:11

Direction — Direction of transfer, encoded as follows:

00b = get direction from TD

01b = OUT

10b = IN

11b = get direction from TC

13

Speed — Specifies cable speed of the endpoint.

0 = full speed (12 Mb/s)

1 = low speed (1.5 Mb/s)

14

Skip — When set the host controller continues to the next ED

without processing any TDs associated with this ED.

15

Format — Defines the format of the TDs linked to this ED.

0 = interrupt, bulk, or control TD format

1 = isochronous TD format

26:16

Maximum Packet Size — Specifies the maximum packet size

supported by this endpoint.

Bit

Field Name

3:0

31:4

Bit

Field Name

Description

0

Halted — When set, this bit indicates that processing of the TD

queue has halted, usually due to an error incurred when pro-

cessing the TD queue.

1

Toggle Carry — This bit contains the value of the toggle bit

when it must be transferred from one TD to the next.

2

A field with zero must be written as a zero by the host control-

ler driver.

31:4

Transfer Descriptor Queue Head Pointer — Points to the next

TD in the list to be processed for this endpoint.

Table D-4: Definition of Endpoint Descriptor Fields (DW3)

Bit

Field Name

Description

3:0

Not Defined — These fields can be used by the host controller

driver for any purpose, and are ignored by the host controller.

31:4

Next Endpoint Descriptor Pointer — Points to next ED descrip-

tor in the linked list. If zero, this indicates the end of the linked

list.

31 30 29 28 27 26 25 24 23

21 20 19 18 17

CC

EC

T

DI

DP

R

--------

31

Current BufferointerP (CBP)

31

Next TD Pointer (NextTD)

31

Memory Buffer End (BE)

Bit

Field Name

Description

17:0

Not Defined — These fields can be used by the host controller

driver for any purpose, and are ignored by the host controller.

Appendix D: Open Host Controller

Table D-5: Definition of Transfer Descriptor Fields (DW0)

Bit

Field Name

Description

18

Buffer Rounding — If zero, this bit specifies that the last data

packet from an endpoint must exactly fill the defined data

buffer. If one, then the last data packet may be smaller than the

defined buffer without causing an error condition.

20:19

Direction/PID — The Packet ID is for this transfer is specified

within this field, which also defines the direction of transfer.

The field is encoded as follows:

00b = Setup (to endpoint)

01b = OUT (to endpoint)

10b = IN (from endpoint)

11b = Reserved

23:21

Delay Interrupt — Contains a delay count that specifies the

number of frames that the host controller must wait before gen-

erating an interrupt, indicating that the TD has completed suc-

cessfully. If this field contains “111b,” then there is no interrupt

associated with completing the TD.

25:24

Data Toggle — The least significant bit of this field contains the

data toggle state. This value is only valid when the most signif-

icant bit of this field is “1.” If the msb of this field is “0,” then

the toggle bit must be obtained from the Toggle Carry within

the ED.

27:26

Error Count — This field contains the error count associated

with transaction errors that have occurred when processing

this transfer descriptor. This field is incremented each time a

transmission error occurs. When the value increments to three,

the error type is recorded in the error condition code field (bits

31:28) and the endpoint is halted. When the TD completes

before three errors occur, this field is reset to zeros.

31:28

Error Condition Code — Specifies the type of error that has

occurred when executing this TD.