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
38
5.6.3.1 Isochronous Out Transactions
Isochronous Out endpoints are used to transfer data from a USB host to the NET2272 local bus. An Isochronous
OUT transaction consists of the following:
Stage
Packet Contents
Number of bytes
Source
OUT Token
OUT PID, address, endpoint, and CRC5
3
Host
Data
DATA0 PID, N data bytes, and CRC16
N+3
Host
The USB host initiates an Isochronous OUT transaction by sending an OUT token to an Isochronous OUT endpoint.
The Data OUT Token Interrupt bit is set when the OUT token is recognized. The bytes corresponding to the Data
stage are stored into the endpoint’s buffer. Isochronous transactions are not retried, so if the buffer is full when a
packet is transferred from the host (or the NAK OUT Packets bit is set), the packet is discarded and the FIFO
Overflow status bit is set. No handshake packets are returned to the host, but the USB OUT ACK Sent, and Timeout
status bits are still set to indicate the status of the transaction. If a CRC error is detected, the packet is accepted and
the Timeout status bit is set. After every data packet is received, the local CPU should sample these status bits to
determine if the NET2272 successfully received the packet.
By definition, isochronous endpoints do not utilize handshaking with the host. Since there is no way to return a stall
handshake from an isochronous endpoint to the host, data that is sent to a stalled isochronous endpoint will be
received normally. The Maximum Packet Size must be less than or equal to the buffer size.
The local CPU must wait for the Data Packet Received Interrupt bit to be set before reading the data from the
buffer. If the endpoint is programmed for a single-buffering, then the host should be programmed to allow the local
CPU enough time to unload the buffer before the next packet is sent. If the endpoint is programmed for double-
buffering, then the local side can unload one packet while the next one is being received.
5.6.3.2 High Bandwidth Isochronous OUT Transactions
The host sends high-bandwidth OUT PID sequences for each microframe depending on the Additional Transaction
Opportunities field in the Endpoint Descriptor as follows:
Additional
Opportunities
PID Sequence
0
DATA0 (normal ISO)
1
MDATA, DATA1 (one extra transaction)
2
MDATA, MDATA, DATA2 (two extra transactions)
The NET2272 accepts data (unless the endpoint buffer is full), and records the PID in the High-Bandwidth OUT
Transaction PID
field of the Endpoint High Bandwidth register. This allows firmware to track PIDs as they arrive
and determine if the data sequence is complete.
High-Bandwidth
OUT Transaction
PID
field
PID Received
00
DATA0
01
DATA1
10
DATA2
11
MDATA
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