H8SXSLASH1663 datasheet(860/1158 Pages) RENESAS

860 / 1158 page

Section 16 USB Function Module (USB)

Rev.1.00 Jun. 07, 2006 Page 808 of 1102

REJ09B0294-0100

16.7.3

Automatic Stall by USB Function Module

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

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

endpoint without regard to the EPSTL register, and returns a stall handshake (1-1 in figure 16.19).

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

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

EPSTL is referenced (3-1 in figure 16.19). The USB function module 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 16.19). To clear a stall, therefore,

the internal status bit must be cleared with a Clear Feature command (3-1 in figure 16.19). If set

by the application, EPSTL should also be cleared (2-1 in figure 16.19).

(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. EPSTL not changed

1. EPSTL cleared to 0

by application

2. IN/OUT token

received from host

3. Internal status bit

already set to 1

4. EPSTL not

referenced

5. Internal status bit

not changed

Normal status restored

Internal status bit

→ 1

EPSTL

Internal status bit

EPSTL

Internal status bit

EPSTL

Internal status bit

→ 0

EPSTL

Stall status maintained

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

Figure 16.19 Automatic Stall by USB Function Module

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