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Philips Semiconductors
ISP1521
Hi-Speed USB hub controller
Product data Rev. 03 — 24 November 2004 24 of 53
9397 750 13702
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
10. Hub controller description
Each USB device is composed of several independent logic endpoints. An endpoint
acts as a terminus of communication flow between the host and the device. At design
time, each endpoint is assigned a unique number (endpoint identifier; see Table 13).
The combination of the device address (given by the host during enumeration), the
endpoint number and the transfer direction allows each endpoint to be uniquely
referenced.
The ISP1521 has two endpoints: endpoint 0 (control) and endpoint 1 (interrupt).
[1] IN: input for the USB host; OUT: output from the USB host.
10.1 Endpoint 0
According to the USB specification, all devices must implement a default control
endpoint. This endpoint is used by the host to configure the USB device. It provides
access to the device configuration and allows generic USB status and control access.
The ISP1521 supports the following descriptor information through its control
endpoint 0:
• Device descriptor
• Device_qualifier descriptor
• Configuration descriptor
• Interface descriptor
• Endpoint descriptor
• Hub descriptor
• Other_speed_configuration descriptor.
The maximum packet size of this endpoint is 64 bytes.
10.2 Endpoint 1
Endpoint 1 can be accessed only after the hub has been configured by the host (by
sending the Set Configuration command). It is used by the ISP1521 to send the
status change information to the host.
Endpoint 1 is an interrupt endpoint. The host polls this endpoint once every 255 ms.
After the hub is configured, an IN token is sent by the host to request the port change
status. If the hub detects no change in the port status, it returns a NAK to this
request, otherwise the Status Change byte is sent. Tabl e 14 shows the content of the
change byte.
Table 13: Hub endpoints
Function Endpoint
identifier
Transfer type Direction
[1]
Maximum packet
size (bytes)
Hub ports 0 to 7 0 control OUT 64
IN 64
1 interrupt IN 1