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Chapter 2. Endpoint Zero Page 2-5

2.3 USB Requests

The

Universal Serial Bus Specification Version 2.0, Chapter 9, "USB Device Framework"

defines a

set of

Standard Device Requests

. When the firmware is in control of endpoint zero (RENUM=1),

the FX2 handles only one of these requests (

Set Address)

automatically; it relies on the firmware

to support all of the others. The firmware acts on device requests by decoding the eight bytes con-

tained in the SETUP packet and available at SETUPDAT. Table2-1 defines these eight bytes.

The Byte column in the previous table shows the byte offset from SETUPDAT. The Field column

shows the different bytes in the request, where the “bm” prefix means bit-map, “b” means byte [8

bits, 0-255], and “w” means word [16 bits, 0-65535].

Table 2-2 shows the different values defined for bRequest, and how the firmware should respond

to each request. The remainder of this chapter describes each of the requests in Tabl e2-2 in

detail.

Table 2-2 applies when RENUM=1, signifying that the firmware, rather than the FX2 hardware,

handles device requests

Table 2-1. The Eight Bytes in a USB SETUP Packet

Byte Field Meaning

0 bmRequestType Request Type, Direction, and Recipient.

1 bRequest The actual request (see Tabl e2-2).

2 wValueL 16-bit value, varies according to bRequest.

3wValueH

4 wIndexL 16-bit field, varies according to bRequest.

5wIndexH

6 wLengthL Number of bytes to transfer if there is a data phase.

7 wLengthH

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 459 460

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