USBN9602 datasheet(21/45 Pages) NSC

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10.0 Endpoint Operation (Continued)

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10.4.1 RFxS

Receive FIFO x Size. This is the total number of bytes

available within the FIFO.

10.4.2 RXRP

Receive Read Pointer. This pointer is incremented every

time the firmware reads from the Receive FIFO. This

pointer wraps around to zero if RFxS is reached. RXRP is

never incremented beyond the value of RXWP.

If the attempt is made to read more bytes than are actual-

ly available (FIFO underrun), the last byte is read repeti-

tively. You should therefore check RCOUNT to obtain an

indication of the number of received bytes remaining.

10.4.3 RXWP

Receive Write Pointer. This pointer is incremented every

time the Endpoint controller writes to the Receive FIFO.

This pointer wraps around to zero if RFxS is reached.

A overrun condition occurs if RXRP equals RXWP and an

attempt is made to receive more bytes.

10.4.4 RxFL

Receive FIFO Level. This value indicates how many more

bytes can be received until an overrun condition occurs

with the next write to the FIFO.

A FIFO warning can be issued if RxFL decreases to a

specific value. The respective FWEV.RXWARNx bit is set

if RxFL is equal to or less than the number specified with

RXCx.RFWL.

10.4.5 RCOUNT

Receive FIFO Count. This value indicates how many

bytes are available to be read out of the Receive FIFO.

This value is accessible by the firmware via the RFSx

10.5 Programming Model

Figure 19 illustrates the register hierarchy. It shows the re-

lationship between the endpoint registers and event regis-

ters.

Figure 18. Rx FIFO Operation

0x0

RXRP

RXWP

RFL = RXRP - RXWP (= RFxS - RCOUNT)

Rx FIFO X

RFxS - 1

FLUSH (resets RXRP and RXWP)

RCOUNT = RXWP - RXRP

USBN9602 Datasheet(PDF) 21 Page - National Semiconductor (TI)

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