Datasheet

542
SAM9G35 [DATASHEET]
11053E–ATARM–10-Mar-2014
32.6.10.2 NYET
NYET is a High Speed only handshake. It is returned by a High Speed endpoint as part of the PING protocol.
High Speed devices must support an improved NAK mechanism for Bulk OUT and control endpoints (except setup
stage). This mechanism allows the device to tell the host whether it has sufficient endpoint space for the next OUT
transfer (see USB 2.0 spec 8.5.1 NAK Limiting via Ping Flow Control).
The NYET/ACK response to a High Speed Bulk OUT transfer and the PING response are automatically handled by
hardware in the UDPHS_EPTCTLx register (except when the user wants to force a NAK response by using the
NYET_DIS bit).
If the endpoint responds instead to the OUT/DATA transaction with an NYET handshake, this means that the endpoint
accepted the data but does not have room for another data payload. The host controller must return to using a PING
token until the endpoint indicates it has space available.
Figure 32-8. NYET Example with Two Endpoint Banks
32.6.10.3 Data IN
32.6.10.4 Bulk IN or Interrupt IN
Data IN packets are sent by the device during the data or the status stage of a control transfer or during an
(interrupt/bulk/isochronous) IN transfer. Data buffers are sent packet by packet under the control of the application or
under the control of the DMA channel.
There are three ways for an application to transfer a buffer in several packets over the USB:
 packet by packet (see 32.6.10.5 below)
 64 KB (see 32.6.10.5 below)
 DMA (see 32.6.10.6 below)
32.6.10.5 Bulk IN or Interrupt IN: Sending a Packet Under Application Control (Device to Host)
The application can write one or several banks.
A simple algorithm can be used by the application to send packets regardless of the number of banks associated to the
endpoint.
Algorithm Description for Each Packet:
 The application waits for TXRDY flag to be cleared in the UDPHS_EPTSTAx register before it can perform a write
access to the DPR.
 The application writes one USB packet of data in the DPR through the 64 KB endpoint logical memory window.
 The application sets TXRDY flag in the UDPHS_EPTSETSTAx register.
The application is notified that it is possible to write a new packet to the DPR by the TXRDY interrupt. This interrupt can
be enabled or masked by setting the TXRDY bit in the UDPHS_EPTCTLENB/UDPHS_EPTCTLDIS register.
Algorithm Description to Fill Several Packets:
Using the previous algorithm, the application is interrupted for each packet. It is possible to reduce the application
overhead by writing linearly several banks at the same time. The AUTO_VALID bit in the UDPHS_EPTCTLx must be set
by writing the AUTO_VALID bit in the UDPHS_EPTCTLENBx register.
t = 0 t = 125 µs t = 250 µs t = 375 µs t = 500 µs t = 625 µs
data 0 ACK data 1 NYET PING ACK data 0 NYET PING NACK PING ACK
Bank 1
Bank 0 Bank 0
Bank 1
Bank 0
Bank 1
Bank 0
Bank 1
Bank 0
Bank 1
Bank 0
Bank 1
Bank 0
Bank 1E
F
F
E
F
E'
F
E
F
F
E'
F
E
F
E: empty
E': begin to empty
F: full