Specification
NET2272 USB Peripheral Controller
______________________________________________________________________________
NetChip Technology, Inc., 2003
Patent Pending
335 Pioneer Way, Mountain View, California 94041
TEL (650) 526-1490
FAX (650) 526-1494
http://www.netchip.com
Rev 1.2, October 15, 2003
34
5.6
USB Endpoints
The NET2272 supports Control, Isochronous, Bulk, and Interrupt endpoints. All endpoints are unidirectional except
for Control endpoints. Bi-directional bulk, isochronous, or interrupt traffic requires two endpoints.
5.6.1 Control Endpoint - Endpoint 0
The control endpoint, Endpoint 0, is a reserved endpoint. The host uses this endpoint to configure and gain
information about the device, its configurations, interfaces and other endpoints. Control endpoints are bi-directional,
and data delivery is guaranteed.
The host sends 8-byte setup packets to Endpoint 0 to which the device interprets and responds. The NET2272 has a
set of registers dedicated to storing the setup packet, and uses the endpoint 0 packet buffer for Control data. For
Control writes, data flows through the packet buffer from the USB bus to the local bus. For Control reads, data
flows through the packet buffer from the local bus to the USB bus.
When Endpoint 0 detects a setup packet, the NET2272 sets status bits and interrupts the local CPU. The CPU reads
the setup packet from NET2272 registers, and responds based on the contents. The local CPU provides any data
returned to the host, including status and descriptors. Refer to Chapter 9, Standard Device Requests, for a
description of the data that must be returned for each USB request. The host will reject descriptors that have
unexpected values in any of the fields.
5.6.1.1 Control Write Transfer
A successful control write transfer to Control Endpoint 0 consists of the following:
Transaction
Stage
Packet Contents
# of
bytes
Source
Setup
Setup Token
SETUP PID, address, endpoint, and CRC5
3
Host
Data
DATA0 PID, 8 data bytes, and CRC16
11
Host
Status
ACK
1
NET2272
Data (zero, one
or more packets)
OUT Token
OUT PID, address, endpoint, and CRC5
3
Host
Data (1/0)
DATA PID, N data bytes, and CRC16
N+3
Host
Status
ACK
1
NET2272
Status
IN Token
IN PID, address, endpoint, and CRC5
3
Host
Data
DATA1 PID, zero length packet, and CRC16
3
NET2272
Status
ACK
1
Host
During the Setup transaction, the NET2272 stores the data stage packet in its setup registers. The NET2272 returns
an ACK handshake to the host after all 8 bytes have been received. A Setup Packet Interrupt bit is set to notify the
local CPU that a setup packet has been received. The 8-byte data packet is then read and interpreted by the local
CPU. A Setup transaction cannot be stalled or NAKed, but if the data is corrupted, then the NET2272 will not return
an ACK to the host.
During the Data transaction, zero, one or more data packets are written into the Endpoint 0 buffer. For each packet:
•
Interrupt bits are set and can interrupt the local CPU
•
The local CPU reads the buffer
•
The NET2272 returns an ACK if no error has occurred.
For a successful Status transaction, the NET2272 returns a zero length data packet. A NAK or STALL handshake
can be returned if an error occurred.
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