USB Device Controller

12-Mbps device and provides the correct polarity for data transmission. The serial bus uses differential signalling to transmit multiple states simultaneously. These states are combined to produce transmit data and various bus conditions, including: Idle, Resume, Start of Packet, End of Packet, Disconnect, Connect, and Reset.

12.2Device Configuration

Table 12-1shows the device’s configuration.

Table 12-1. Endpoint Configuration

Endpoint Number

Type

Function

FIFO Size (bytes) X

number of FIFOs

 

 

 

 

 

 

 

0

Control

IN/OUT

16

 

 

 

 

1

Bulk

IN

64x2

 

 

 

 

2

Bulk

OUT

64x2

 

 

 

 

3

Isochronous

IN

256x2

 

 

 

 

4

Isochronous

OUT

256x2

 

 

 

 

5

Interrupt

IN

8

 

 

 

 

6

Bulk

IN

64x2

 

 

 

 

7

Bulk

OUT

64x2

 

 

 

 

8

Isochronous

IN

256x2

 

 

 

 

9

Isochronous

OUT

256x2

 

 

 

 

10

Interrupt

IN

8

 

 

 

 

11

Bulk

IN

64x2

 

 

 

 

12

Bulk

OUT

64x2

 

 

 

 

13

Isochronous

IN

256x2

 

 

 

 

14

Isochronous

OUT

256x2

 

 

 

 

15

Interrupt

IN

8

 

 

 

 

Data flow is relative to the USB host. IN packets represent data flow from the UDC to the host. OUT packets represent data flow from the host to the UDC.

The FIFOs for the Bulk and Isochronous endpoints are double-buffered so one packet can be processed as the next is assembled. While the UDC transmits an IN packet from a particular endpoint, the Megacell can load the same endpoint for the next frame transmission. While the Megacell unloads an OUT endpoint, the UDC can continue to process the next incoming packet to that endpoint.

12.3USB Protocol

After a core reset or when the USB host issues a USB reset, the UDC configures all endpoints and is forced to use the USB default address, zero. After the UDC configures the endpoints, the host assigns the UDC a unique address. At this point, the UDC is under the host’s control and responds to commands that use control transactions to transmit to endpoint 0.

12-2

Intel® PXA255 Processor Developer’s Manual

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Intel PXA255 manual Device Configuration, USB Protocol, Endpoint Configuration, In/Out