Atmel SAM9X25, Manual

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Figure 33-8. NYET Example with Two Endpoint Banks
33.6.9.3 Data IN
33.6.9.4 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 33.6.9.5 below)
•
64
KB (see 33.6.9.5 below)
• DMA (see 33.6.9.6 below)
33.6.9.5 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 TX_PK_RDY 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 TX_PK_RDY flag in the UDPHS_EPTSETSTAx register.
The application is notified that it is possible to write a new packet to the DPR by the
TX_PK_RDY interrupt. This interrupt can be enabled or masked by setting the TX_PK_RDY 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.
The auto-valid-bank mechanism allows the transfer of data (IN and OUT) without the interven-
tion of the CPU. This means that bank validation (set TX_PK_RDY or clear the RX_BK_RDY bit)
is done by hardware.
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 1 E
F
F
E
F
E'
F
E
F
F
E'
F
E
F
E: empty
E': begin to empty
F: full