at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 411

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Stall Handshake
1790A–ATARM–11/03
A stall handshake can be used in one of two distinct occasions. (For more information on the
stall handshake, refer to Chapter 8 of the Universal Serial Bus Specification, Rev 2.0.)
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The following procedure generates a stall packet:
1. The microcontroller sets the FORCESTALL flag in the USB_CSRx endpoint’s register.
2. The host receives the stall packet.
3. The microcontroller is notified that the device has sent the stall by polling the
When a setup transaction is received after a stall handshake, STALLSENT must be cleared in
order to prevent interrupts due to STALLSENT being set.
Figure 174. Stall Handshake (Data IN Transfer)
Figure 175. Stall Handshake (Data OUT Transfer)
USB Bus
Packets
STALLSENT
FORCESTALL
USB Bus
Packets
FORCESTALL
STALLSENT
A functional stall is used when the halt feature associated with the endpoint is set. (Refer
to Chapter 9 of the Universal Serial Bus Specification, Rev 2.0, for more information on the
halt feature.)
To abort the current request, a protocol stall is used, but uniquely with control transfer.
STALLSENT to be set. An endpoint interrupt is pending while STALLSENT is set. The
microcontroller must clear STALLSENT to clear the interrupt.
Data OUT PID
Data IN
PID
Set by USB Device
Data OUT
Stall PID
Set by Firmware
Stall PID
Set by Firmware
Interrupt Pending
Interrupt Pending
Set by
USB Device
Cleared by Firmware
AT91RM3400
Cleared by Firmware
Cleared by Firmware
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