DOC7707 datasheet(202/307 Pages) ETC1

202 / 307 page

202

7707F–AVR–11/10

AT90USB82/162

20.12.2

Control Read

The next figure shows a control read transaction. The USB controller has to manage the simulta-

neous write requests from the CPU and the USB host:

A NAK handshake is always generated at the first status stage command.

When the controller detect the status stage, all the data writen by the CPU are erased, and

clearing TXINI has no effects.

The firmware checks if the transmission is complete or if the reception is complete.

The OUT retry is always ack’ed. This reception:

- set the RXOUTI flag (received OUT data)

- set the TXINI flag (data sent, ready to accept new data)

software algorithm:

set transmit ready

wait (transmit complete OR Receive complete)

if receive complete, clear flag and return

if transmit complete, continue

Once the OUT status stage has been received, the USB controller waits for a SETUP request.

The SETUP request have priority over any other request and has to be ACK’ed. This means that

any other flag should be cleared and the fifo reset when a SETUP is received.

WARNING: the byte counter is reset when a OUT Zero Length Packet is received. The firmware

has to take care of this.

20.13 OUT endpoint management

OUT packets are sent by the host. All the data can be read by the CPU, which acknowledges or

not the bank when it is empty.

20.13.1

Overview

The Endpoint must be configured first.

SETUP

RXSTPI

RXOUTI

TXINI

USB line

OUT

NAK

Wr Enable

HOST

Wr Enable

CPU

DATA

SETUP

STATUS

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