SH7721 datasheet(908/1524 Pages) RENESAS

908 / 1524 page

Section 25

USB Function Controller (USBF)

Rev. 3.00 Jan. 18, 2008 Page 846 of 1458

REJ09B0033-0300

25.4.5

EP2 Bulk-In Transfer (Dual FIFOs)

USB function

Application

IN token reception

Data transmission to host

Clear EP2 transfer

request flag

(IFR0/EP2 TR = 0)

Enable EP2 FIFO

empty interrupt

(IER0/EP2 EMPTY = 1)

IFR0/EP2 EMPTY

interrupt

Write one packet of data

to EP2 data register

(EPDR2)

Write 1 to EP2 packet

enable bit

(TRG/EP2 PKTE = 1)

Set EP2

empty status

(IFR0/EP2

EMPTY = 1)

Valid data

in EP2 FIFO?

NAK

ACK

Interrupt request

Yes

Clear EP2 empty status

(IFR0/EP2 EMPTY = 0)

Space

in EP2 FIFO?

Yes

Interrupt

request

Figure 25.12

EP2 Bulk-In Transfer Operation

EP2 has two 64-byte FIFOs, but the user can perform data transmission and transmit data writes

without being aware of this dual-FIFO configuration. However, one data write is performed for

one FIFO. For example, even if both FIFOs are empty, it is not possible to perform EP2/PKTE at

one time after consecutively writing 128 bytes of data. EP2/PKTE must be performed for each 64-

byte write.

When performing bulk-in transfer, as there is no valid data in the FIFOs on reception of the first

IN token, an IFR0/EP2 TR interrupt is requested. With this interrupt, 1 is written to the IER0/EP2

EMPTY bit, and the EP2 FIFO empty interrupt is enabled. At first, both EP2 FIFOs are empty,

and so an EP2 FIFO empty interrupt is generated immediately.

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