SH7721 datasheet(920/1524 Pages) RENESAS

920 / 1524 page

Section 25

USB Function Controller (USBF)

Rev. 3.00 Jan. 18, 2008 Page 858 of 1458

REJ09B0033-0300

25.8.3

Automatic Stall by USB Function Controller

When a stall setting is made with the Set Feature command, or in the event of a USB specification

violation, the USB function controller automatically sets the internal status bit for the relevant

endpoint without regard to the corresponding bit in EPSTL, and returns a stall handshake (1-1 in

figure 25.19).

Once an internal status bit is set, it remains set until cleared by a Clear Feature command from the

host, without regard to the corresponding bit in EPSTL. After a bit is cleared by the Clear Feature

command, the corresponding bit in EPSTL is referenced (3-1 in figure 25.19). The USB function

controller continues to return a stall handshake while the internal status bit is set, since the internal

status bit is set even if a transaction is executed for the corresponding endpoint (2-1 and 2-2 in

figure 25.19). To clear a stall, therefore, the internal status bit must be cleared with a Clear Feature

command (3-1 in figure 25.19). In this time, if set by the application, the corresponding bit in

EPSTL should also be cleared (2-1 in figure 25.19).

(1) Transition from normal operation to stall

(1-1)

(2) When transaction is performed when internal status bit is set, and Clear Feature is sent

(2-1)

STALL handshake

Transaction request

STALL handshake

(2-2)

Clear Feature command

(3) When Clear Feature is sent before transaction is performed

(3-1)

1. In case of USB

specification

violation, etc., USB

function module

stalls endpoint

automatically

1. Transmission of

STALL handshake

1. Internal status bit

cleared to 0

2. EPnSTL not changed

1. EPnSTL cleared to

0 by application

2. IN/OUT token

received from host

3. Internal status bit

already set to 1

4. EPnSTL not

referenced

5. Internal status bit

not changed

Normal status restored

Internal status bit

→ 1

EPnSTL

Internal status bit

EPnSTL

Internal status bit

EPnSTL

Internal status bit

→ 0

EPnSTL

Stall status maintained

To (2-1) or (3-1)

Figure 25.19

Automatic Stall by USB Function Controller

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