AT572D940HF_14 Datasheet, PDF (576/745 Pages) ATMEL Corporation – High Performance MagicV VLIW DSP

A status transaction is a special type of host-to-device transaction used only in a control transfer.
The control transfer must be performed using endpoints with no ping-pong attributes. According
to the control sequence (read or write), the USB device sends or receives a status transaction.
Figure 31-5. Control Read and Write Sequences
Setup Stage
Data Stage
Status Stage
Control Read
Setup TX
Data OUT TX
Data OUT TX
Setup Stage
Data Stage
Status IN TX
Status Stage
Control Write
Setup TX
Data IN TX
Setup Stage
Status Stage
Data IN TX
Status OUT TX
No Data
Control
Setup TX
Status IN TX
Notes:
1. During the Status IN stage, the host waits for a zero length packet (Data IN transaction with no data) from the device using
DATA1 PID. Refer to Chapter 8 of the Universal Serial Bus Specification, Rev. 2.0, for more information on the protocol
layer.
2. During the Status OUT stage, the host emits a zero length packet to the device (Data OUT transaction with no data).
31.5.2 Handling Transactions with USB V2.0 Device Peripheral
31.5.2.1
Setup Transaction
Setup is a special type of host-to-device transaction used during control transfers. Control trans-
fers must be performed using endpoints with no ping-pong attributes. A setup transaction needs
to be handled as soon as possible by the firmware. It is used to transmit requests from the host
to the device. These requests are then handled by the USB device and may require more argu-
ments. The arguments are sent to the device by a Data OUT transaction which follows the setup
transaction. These requests may also return data. The data is carried out to the host by the next
Data IN transaction which follows the setup transaction. A status transaction ends the control
transfer.
When a setup transfer is received by the USB endpoint:
• The USB device automatically acknowledges the setup packet
• RXSETUP is set in the UDP_ CSRx register
• An endpoint interrupt is generated while the RXSETUP is not cleared. This interrupt is carried
out to the microcontroller if interrupts are enabled for this endpoint.
576 AT572D940HF Preliminary
7010A–DSP–07/08