Datasheet

444
6120F–ATARM–03-Oct-06
AT91SAM7X512/256/128 Preliminary
Figure 34-6. Data IN Transfer for Non Ping-pong Endpoint
34.5.2.4 Using Endpoints With Ping-pong Attribute
The use of an endpoint with ping-pong attributes is necessary during isochronous transfer. This
also allows handling the maximum bandwidth defined in the USB specification during bulk trans-
fer. To be able to guarantee a constant or the maximum bandwidth, the microcontroller must
prepare the next data payload to be sent while the current one is being sent 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 34-7. Bank Swapping Data IN Transfer for Ping-pong Endpoints
USB Bus Packets
Data IN 2
Data IN NAK
ACK
Data IN 1
FIFO (DPR)
Content
Data IN 2Load In ProgressData IN 1
Cleared by Firmware
DPR access by the firmware
Payload in FIFO
TXCOMP Flag
(UDP_CSRx)
TXPKTRDY Flag
(UDP_CSRx)
PID
Data IN Data IN
PIDPID PIDPID
ACK
PID
Prevous Data IN TX Microcontroller Load Data in FIFO Data is Sent on USB Bus
Interrupt
Pending
Interrupt Pending
Set by the firmware
Set by the firmware
Cleared by
Firmware
Cleared by Hw
Cleared by Hw
DPR access by the hardware
USB Device USB Bus
Read
Write
Read and Write 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