Cypress Semiconductor FX2LP Información técnica Pagina 55

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Chapter 2. Endpoint Zero Page 2-1
Chapter 2 Endpoint Zero
2.1 Introduction
Endpoint zero has special significance in a USB system. It is a CONTROL endpoint, and it is
required by every USB device. The USB host uses special SETUP tokens to signal transfers that
deal with device control; only CONTROL endpoints accept these special tokens.
The USB host sends a suite of standard device requests over endpoint zero. These standard
requests are fully defined in Chapter 9 of the USB Specification. This chapter describes how the
FX2 chip handles endpoint zero requests.
The FX2 provides extensive hardware support for handling endpoint-zero operations; this chapter
describes those operations and the FX2 resources that simplify the firmware which handles them.
Endpoint zero is the only CONTROL endpoint supported by the FX2. CONTROL endpoints are
bi-directional, so the FX2 provides a single 64-byte buffer, EP0BUF, which firmware handles
exactly like a bulk endpoint buffer for the data stages of a CONTROL transfer. A second 8-byte
buffer called SETUPDAT, which is unique to endpoint zero, holds data that arrives in the SETUP
stage of a CONTROL transfer. This relieves the FX2 firmware of the burden of tracking the three
CONTROL transfer phases (SETUP, DATA, and STATUS). The FX2 also generates separate inter-
rupt requests for the various transfer phases, further simplifying code.
Endpoint zero is always enabled and accessible by the USB host.
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