Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
596
36.6.2.7 Using Endpoints With Ping-pong Attributes
During isochronous transfer, using an endpoint with ping-pong attributes is obligatory. To be able to guarantee a
constant bandwidth, the microcontroller must read the previous data payload sent by the host, while the current
data payload is received by the USB device. Thus two banks of memory are used. While one is available for the
microcontroller, the other one is locked by the USB device.
Figure 36-10. Bank Swapping in Data OUT Transfers for Ping-pong Endpoints
When using a ping-pong endpoint, the following procedures are required to perform Data OUT transactions:
1. The host generates a Data OUT packet.
2. This packet is received by the USB device endpoint. It is written in the endpoint’s FIFO Bank 0.
3. The USB device sends an ACK PID packet to the host. The host can immediately send a second Data OUT
packet. It is accepted by the device and copied to FIFO Bank 1.
4. The microcontroller is notified that the USB device has received a data payload, polling RX_DATA_BK0 in
the endpoint’s UDP_CSRx. An interrupt is pending for this endpoint while RX_DATA_BK0 is set.
5. The number of bytes available in the FIFO is made available by reading RXBYTECNT in the endpoint’s
UDP_CSRx.
6. The microcontroller transfers out data received from the endpoint’s memory to the microcontroller’s memory.
Data received is made available by reading the endpoint’s UDP_FDRx.
7. The microcontroller notifies the USB peripheral device that it has finished the transfer by clearing
RX_DATA_BK0 in the endpoint’s UDP_CSRx.
8. A third Data OUT packet can be accepted by the USB peripheral device and copied in the FIFO Bank 0.
9. If a second Data OUT packet has been received, the microcontroller is notified by the flag RX_DATA_BK1
set in the endpoint’s UDP_CSRx. An interrupt is pending for this endpoint while RX_DATA_BK1 is set.
10. The microcontroller transfers out data received from the endpoint’s memory to the microcontroller’s memory.
Data received is available by reading the endpoint’s UDP_FDRx.
11. The microcontroller notifies the USB device it has finished the transfer by clearing RX_DATA_BK1 in the
endpoint’s UDP_CSRx.
12. A fourth Data OUT packet can be accepted by the USB device and copied in the FIFO Bank 0.
USB Device USB Bus
Read
Write
Write and Read at the Same Time
1
st
Data Payload
2
nd
Data Payload
3
rd
Data Payload
3
rd
Data Payload
2
nd
Data Payload
1
st
Data Payload
Data IN Packet
Data IN Packet
Data IN Packet
Microcontroller
Endpoint 1
Bank 0
Endpoint 1
Bank 1
Endpoint 1
Bank 0
Endpoint 1
Bank 0
Endpoint 1
Bank 0
Endpoint 1
Bank 1