net2890 ETC-unknow, net2890 Datasheet - Page 24

• Manufacturer Part Number: net2890
• Description: Interface Controller
• Manufacturer: ETC-unknow

Specification
4.5.3.2 Isochronous In Transactions
Isochronous In endpoints are used to transfer data from the NET2890 local bus to a USB host. An
isochronous IN transaction consists of the following:
The USB host initiates an Isochronous IN transaction by sending an IN token to an Isochronous IN
endpoint. The Data IN Token Interrupt status bit is set when the IN token is recognized. If this interrupt
is enabled, the local interrupt IRQ# pin is asserted. If there is data in the endpoint’s FIFO, it is returned to
the host. If the endpoint has no data to return, a zero length packet is returned to the host. The NET2890
responds to the IN token according to the following table.
FIFO
Valid
Mode
0
0
0
0
0
1
1
1
1
After the packet has been sent to the host, the Data Packet Transmitted Interrupt status bit is set. If this
interrupt is enabled, the local interrupt IRQ# pin is asserted. No handshake packets are returned to the host,
but the USB IN ACK Sent, USB IN NAK 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 acknowledge from an isochronous endpoint to the host, data which is sent to a stalled
isochronous endpoint will be received normally.
____________________________________________________________________________________
Stage
IN Token
Data
FIFO
Valid
Bit
0
0
0
1
X
0
X
1
1
End of
Transfer
Response Bit
0
1
1
X
X
X
X
X
X
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Packet Contents
IN PID, address, endpoint, and CRC5
DATA0 PID, N data bytes, and CRC16
Size of
Previous
Packet
X
Maximum
< Maximum
X
X
X
X
X
X
NetChip Technology, Inc., 1999
Rev 2.0, Draft 9, July 16, 1999
http://www.netchip.com
Amount of Data in
FIFO
empty
empty
empty
empty
>0
< Max Packet Length
>= Max Packet Length
empty
>0
NET2890 USB Interface Controller
bytes
N+3
# of
Action
Zero length packet to host;
USB IN NAK Sent status
bit set
Zero length packet to host
Zero length packet to host;
USB IN NAK Sent status
bit set
Zero length packet to host
Return data to host
Zero length packet to host;
USB IN NAK Sent status
bit set
Return data to host
Zero length packet to host
Return data to host
3
NET2890
Source
Host
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