H8SSLASH2218 datasheet(567/750 Pages) RENESAS

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Section 14 Universal Serial Bus (USB)

Rev.6.00 Jun. 03, 2008 Page 519 of 698

REJ09B0074-0600

(3) Automatic Stall by USB Function Module

When a stall setting is made with the Set Feature command, when the information of this

module differs from that returned to the host by the Get Descriptor, or in the event of a USB

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

the corresponding endpoint without regarding to EPnSTL, and returns a stall handshake (1-1 in

figure 14.21).

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

the host, without regarding to EPnSTL. After a bit is cleared by the Clear Feature command,

EPnSTL is referred (3-1 in figure 14.21). 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 14.21). To clear a

stall, therefore, the internal status bit must be cleared with a Clear Feature command (3-1 in

figure 14.21). If set by the firmware, EPnSTL should also be cleared (2-1 in figure 14.21).

(1)

Transition from normal operation to stall

(2)

When transaction is performed whill internal status bit is set

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,

USB function module

stalls endpoint

automatically.

1. Transmit stall

handshake

1. Clear the internal

status bit to 0

2. No change in

EPnSTL bit

1. Receive IN/OUT

token from the host

2. Internal status bit has

been set to 1

3. EPnSTL is not

referred to

4. No change internal

status bit

Normal status restored

Internal status bit

→ 1

EPnSTL

Internal status bit

EPnSTL

Internal status bit

EPnSTL

Internal status bit

→ 0

EPnSTL

Stall status maintained

USB function module

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

(1-1)

(2-1)

Figure 14.21 Automatic Stall by USB Function Module

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