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
30
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 NET2270 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 NET2270, the Packet Received interrupt is set. The NET2270 can
handle any number of back-to-back retries, but the host determines how many times a packet is retried. Microsoft
Windows currently performs three retries before giving up on the device.
5.3.2 In Transactions
If an error occurs during an IN transaction, the NET2270 reloads its USB side buffer read pointer back to the
beginning of the failed packet. The host then sends another IN token and the NET2270 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 NET2270 supports the PING protocol for bulk OUT and control
endpoints. This protocol allows the NET2270 to indicate to the host that it can't accept an OUT data packet. The
host then sends PING tokens to query the NET2270. Once the NET2270 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 NET2270
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 NET2270 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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