Cypress Semiconductor FX2LP Informacje Techniczne Strona 66

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EZ-USB FX2 Technical Reference Manual
Page 2-12 EZ-USB FX2 Technical Reference Manual v2.1
If the USB device supports remote wakeup (reported in its descriptor table when the device enu-
merates), the Clear Feature/Remote Wakeup request disables the wakeup capability.
The Clear Feature/Stall removes the stall condition from an endpoint. The firmware should
respond by clearing the STALL bit in the indicated endpoint’s EPxCS register.
2.3.4 Get Descriptor
During enumeration, the host queries a USB device to learn its capabilities and requirements
using Get Descriptor requests. Using tables of descriptors, the device sends back (over EP0-IN)
such information as what device driver to load, how many endpoints it has, its different configura-
tions, alternate settings it may use, and informative text strings about the device.
The FX2 provides a special Setup Data Pointer to simplify firmware service for Get_Descriptor
requests. The firmware loads this 16-bit pointer with the starting address of the requested descrip-
tor, clears the HSNAK bit (by writing 1 to it), and the FX2 transfers the entire descriptor.
Table 2-9. Clear Feature-Endpoint (Clear Stall)
Byte Field Value Meaning Firmware Response
0 bmRequestType 0x02 OUT, Endpoint
Clear the STALL bit for the
1 bRequest
0x01
“Clear Feature”
indicated endpoint.
2 wValueL 0x00 Feature Selector:
3 wValueH 0x00 STALL
4 wIndexL EP 0x00-0x08: OUT0-OUT8
5 wIndexH 0x00 0x80-0x88: IN0-IN8
6 wLengthL 0x00
7 wLengthH 0x00
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