NET2890 datasheet(18/73 Pages) ETC

18 / 73 page

Specification

NET2890 USB Interface Controller

____________________________________________________________________________________

NetChip Technology, Inc., 1999

335 Pioneer Way, Mountain View, California 94041

TEL (650) 526-1490

FAX (650) 526-1494

http://www.netchip.com

Rev 2.0, Draft 9, July 16, 1999

4.3 Automatic Retries

4.3.1 Out Transactions

If an error occurs during an OUT transaction, the NET2890 reloads its local side FIFO 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 NET2890, the Packet Received interrupt is set. The

NET2890 can handle any number of back-to-back retries, but the host determines how many times a packet

is retried. Windows 98 currently performs three retries before giving up on the device.

4.3.2 In Transactions

If an error occurs during an IN transaction, the NET2890 reloads its USB side FIFO read pointer back to

the beginning of the failed packet. The host then sends another IN token and the NET2890 re-transmits the

packet. Once the packet has been successfully received by the host, the Packet Transmitted interrupt is set.

If additional data is written to the FIFO after the failed packet, and the failed packet was less than the

maximum packet size, then the re-transmitted packet may be larger than the failed packet.

4.4 Packet Lengths

The maximum packet length of an endpoint is determined by the corresponding ‘Max Packet Size’ register.

For IN transactions, the NET2890 will return a maximum size packet to the host if there are at least ‘max

packet’ bytes in the FIFO. A packet of size less than ‘Max Packet Size’ is returned to the host in response

to an IN token if either of the following are true

•

FIFO Valid Mode (FIFOCTL[6]) and FIFO Valid (FIFOSTAT[7]) are both true

•

FIFO Valid Mode (FIFOCTL[6]) is false

4.5 USB Endpoints

The NET2890 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.

4.5.1 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

NET2890 has a set of registers dedicated to storing the setup packet, as well as a dedicated 16-byte bi-

directional FIFO for Control data. For Control writes, data flows through the FIFO from the USB bus to

the local bus. For Control reads, data flows through the FIFO from the local bus to the USB bus.

When Endpoint 0 detects a setup packet, the NET2890 sets status bits and interrupts the local CPU. The

CPU reads the setup packet from NET2890 registers, and responds based on the contents. Any data

returned to the host, including status and descriptors, is provided by the local CPU. Refer to the Chapter 6,

Standard Device Requests, for a description of the data which must be returned for each USB request.

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