7643 datasheet(246/424 Pages) RENESAS

246 / 424 page

Rev.2.00

Aug 28, 2006

page 125 of 202

7643 Group

REJ09B0133-0200

APPLICATION

2.6 USB

(1)

Interrupt transfer

Endpoints 1 to 2 can be used in interrupt transfer mode. During a regular interrupt transfer, an

interrupt transaction is similar to the bulk transfer. Therefore, there is no special setting required.

When IN-endpoint is used for a rate feedback interrupt transfer, INTPT bit of the IN_CSR register

must be set to “1”. The following steps show how to configure the IN-endpoint for the rate feedback

interrupt transfer.

1. Set a value which is larger than 1/2 of the USB endpoint-x FIFO size to the USB endpoint x

IN max. package size register.

2. Set INTPT bit to “1”.

3. Flush the old data in the FIFO.

4. Store transmission data to the IN FIFO and set the IN_PKT_RDY bit to “1”.

5. Repeat steps 3 and 4.

In a real application, the function-side always has transfer data when the function sends an

endpoint in a rate feedback interrupt. Accordingly, the USB FCU never returns a NAK against the

host IN token for the rate feedback interrupt. The USB FCU always transmits data in the FIFO in

response to an IN token, regardless of IN_PKT_RDY. However, this premises that there is always

an ACK response from Host PC after the 7643 Group has transmitted data to IN token.

(2)

Usage notes concerning data transmit

Usage notes concerning IN FIFO

Determine the number of data packets in the IN FIFO by the value of the IN_PKT_RDY bit and

the TX_NOT_EPT flag. Erase the contents of the USB endpoint x IN FIFO by setting the FLUSH

bit to “1”. This will also modify the state of the IN_PKT_RDY bit and the TX_NOT_EPT flag.

If there are two packets in the FIFO, the older packet will be erased.

Table 2.6.2 shows the states of the IN FIFO.

Table 2.6.2 IN FIFO States

IN_PKT_RDY

TX_NOT_EMP

IN FIFO States

No data packet

1 data packet (max. packet size

≤ 1/2 IN FIFO size)

In valid if max. packet size > 1/2 size

Invalid

1 data packet (max. packet size > 1/2 size)

2 data packets (max. packet size

≤ 1/2 IN FIFO size)

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