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
33
5.2.3 Transaction
A transaction consists of a token packet, optional data packet(s), and a handshake packet.
5.2.4 Transfer
A transfer consists of one or more transactions. Control transfers consist of a setup transaction, optional data
transactions, and a handshake (status) transaction.
5.3
Automatic Retries
5.3.1 Out Transactions
If an error occurs during an OUT transaction, the NET2272 reloads its local side buffer read pointer back to the
beginning of the failed packet. The host then sends another OUT token and re-transmits the packet. Once the
packet has been successfully received by the NET2272, the Packet Received interrupt is set. The NET2272 can
handle any number of back-to-back retries, but the host determines how many times a packet is retried.
5.3.2 In Transactions
If an error occurs during an IN transaction, the NET2272 reloads its USB side buffer read pointer back to the
beginning of the failed packet. The host then sends another IN token and the NET2272 re-transmits the packet.
Once the host has successfully received the packet, the Packet Transmitted interrupt is set.
5.4
Ping Flow Control
When operating in high speed mode, the NET2272 supports the PING protocol for bulk OUT and control endpoints.
This protocol allows the NET2272 to indicate to the host that it can't accept an OUT data packet. The host then
sends PING tokens to query the NET2272. Once the NET2272 can accept a maximum size packet, it returns an
ACK in response to the PING. Now the host sends an OUT token and data packet. The NET2272 returns an ACK
handshake if the packet is accepted, and there is space to receive an additional packet. If it can accept the current
packet, but no others, it returns a NYET handshake to the host. The host then starts sending PING tokens again.
5.5
Packet Sizes
The maximum packet size of an endpoint is determined by the corresponding EP_MAXPKT register. For IN
transactions, the NET2272 will return a maximum size packet to the host if there are at least ‘max packet’ bytes in
the buffer. A packet of size less than the maximum is returned to the host in response to an IN token if the data in
the buffer has been explicitly validated.
The following table shows the allowable maximum packet sizes:
Type of Endpoint
Low Speed Mode
(Not Supported)
Full Speed Mode
High Speed Mode
Control
8
8, 16, 32, 64
64
Bulk
N/A
8, 16, 32, 64
512
Interrupt
8
64 max
1024 max
Isochronous
N/A
1023 max
1024 max
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