M66596FP datasheet(96/131 Pages) RENESAS

96 / 131 page

M66596FP/WG

rev .1.00

2006.3.14

page 96 of 127

3.9.5

Isochronous transfer transmission buffer flush

In the Peripheral mode if a (u) SOF packet is received without an IN token having been received in the interval

frame during isochronous data transmission, the controller operates as a IN token had been corrupted, and clears

the buffer for which transmission is enabled, putting that buffer in the writing enabled state.

If a double buffer is being used at that time and writing has been finished to both buffers, the buffer memory that

was cleared is seen as the data having been sent at the same interval frame, and transmission is enabled for the

other buffer memory.

The timing at which the operation of the buffer flush function begins varies depending on the value set for the

IITV bit.

(1)

If IITV=0

The buffer flush operation starts from the next frame after the pipe becomes valid.

(2)

In any case other than IITV=0

The buffer flush operation is carried out subsequent to the first normal transaction.

Figure 3.27 shows an example of the buffer flush function of the controller. When an unanticipated token prior to

the interval frame is received, the controller sends the written data or a Zero-Length packet are sent in accordance

with buffer state.

Transmission enabled state

Writing in

progress

Buffer A

Buffer B

Writing completed

Empty state

Writing in

progress

Writing completed

Writing in

progress

Writing completed

Transmission enabled state

Figure 3.27 Example of buffer flush function operation

Figure 3.28 shows an example of the controller generating an interval error. There are five types of interval errors,

as noted below. The interval error is generated at the timing indicated by

in the illustration, and the buffer flush

function is activated.

If the interval error occurs during an IN transfer, the buffer flush function is activated, and if it occurs during an

OUT transfer an NRDY interrupt is generated.

The OVRN bit should be used to distinguish between NRDY interrupts such as received packet errors and overrun

errors.

In response to tokens that are shaded in the illustration, responses occur based on the buffer memory status.

(1)

IN direction

(a) If the buffer is in the transmission enabled state, the data is transferred as a normal response .

(b) If the buffer is in the transmission disabled state, a Zero-Length packet is sent and an underrun error

occurs.

(2)

OUT direction

(a) If the buffer is in the reception enabled state, the data is received as a normal response.

(b) If the buffer is in the reception disabled state, the data is decarded and an overrun error occurs.

Token

Normal transfer

Token

Token damaged

Token

Token delayed

Token

Frame misaligned

Token

Packet inserted

Token

SOF

Frame misaligned

Figure 3.28 Example of interval error being generated when “IITV=1”

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