Specification
NET2270 USB Interface Controller
______________________________________________________________________________
NetChip Technology, Inc., 2003
335 Pioneer Way, Mountain View, California 94041
TEL (650) 526-1490
FAX (650) 526-1494
http://www.netchip.com
Rev 3.6, April 17, 2003
36
5.6.3.2 Isochronous In Transactions
Isochronous IN endpoints are used to transfer data from the NET2270 local bus to a USB host. An isochronous IN
transaction consists of the following:
Stage
Packet Contents
Number of bytes
Source
IN Token
IN PID, address, endpoint, and CRC5
3
Host
Data
DATA0 PID, N data bytes, and CRC16
N+3
NET2270
The USB host initiates an Isochronous IN transaction by sending an IN token to an Isochronous IN endpoint. The
Data IN Token Interrupt bit is set when the IN token is recognized. If there is data in the endpoint’s buffer, it is
returned to the host. If the endpoint has no data to return, a zero length packet is returned to the host. The
NET2270 responds to the IN token according to the following table.
Packet Validated
Amount of Data in Buffer
Action
0
< Max Packet Size
Zero length packet to host; USB
IN NAK Sent status bit set
X
>= Max Packet Size
Return data to host.
1
empty
Zero length packet to host
1
>0
Return data to host
After the packet has been sent to the host, the Data Packet Transmitted Interrupt bit is set. If an IN token arrives
and there is no valid packet in the endpoint buffer, the NET2270 returns a zero-length packet, and the FIFO
Underflow status bit is set. No handshake packets are returned to the host, but the USB IN ACK Sent, and Timeout
status bits are still set to indicate the status of the transaction. After every data packet is transmitted, the local CPU
should sample these status bits to determine if the packet was successfully transmitted to the host.
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 requested from a stalled isochronous endpoint will
be transmitted normally.
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