Datasheet

 2017 Microchip Technology Inc. DS60001516A-page 663
SAM9G20
Figure 36-5: Setup Transaction Followed by a Data OUT Transaction
36.5.2.2 Data IN Transaction
Data IN transactions are used in control, isochronous, bulk and interrupt transfers and conduct the transfer of data from the device to the
host. Data IN transactions in isochronous transfer must be done using endpoints with ping-pong attributes.
• Using Endpoints Without Ping-pong Attributes
To perform a Data IN transaction using a non ping-pong endpoint:
1. The application checks if it is possible to write in the FIFO by polling TXPKTRDY in the endpoint’s UDP_CSRx register (TXPKTRDY
must be cleared).
2. The application writes the first packet of data to be sent in the endpoint’s FIFO, writing zero or more byte values in the endpoint’s
UDP_FDRx register,
3. The application notifies the USB peripheral it has finished by setting the TXPKTRDY in the endpoint’s UDP_CSRx register.
4. The application is notified that the endpoint’s FIFO has been released by the USB device when TXCOMP in the endpoint’s
UDP_CSRx register has been set. Then an interrupt for the corresponding endpoint is pending while TXCOMP is set.
5. The microcontroller writes the second packet of data to be sent in the endpoint’s FIFO, writing zero or more byte values in the end-
point’s UDP_FDRx register,
6. The microcontroller notifies the USB peripheral it has finished by setting the TXPKTRDY in the endpoint’s UDP_CSRx register.
7. The application clears the TXCOMP in the endpoint’s UDP_CSRx.
After the last packet has been sent, the application must clear TXCOMP once this has been set.
TXCOMP is set by the USB device when it has received an ACK PID signal for the Data IN packet. An interrupt is pending while TXCOMP
is set.
Warning: TX_COMP must be cleared after TX_PKTRDY has been set.
Note: Refer to Chapter 8 of the Universal Serial Bus Specification, Rev 2.0, for more information on the Data IN protocol layer.
RX_Data_BKO
(UDP_CSRx)
ACK
PID
Data OUT
Data OUT
PID
NAK
PID
ACK
PID
Data Setup
Setup
PID
USB
Bus Packets
RXSETUP Flag
Set by USB Device Cleared by Firmware
Set by USB
Device Peripheral
FIFO (DPR)
Content
Data Setup
Data
XX XX
OUT
Interrupt Pending
Setup Received Setup Handled by Firmware Data Out Received
Data OUT
Data OUT
PID