Datasheet

514
SAM9X35 [DATASHEET]
11055E–ATARM–10-Mar-2014
A transfer descriptor can be used. Instead of programming the register directly, a descriptor should be programmed and
the address of this descriptor is then given to UDPHS_DMANXTDSC to be processed after setting the LDNXT_DSC field
(Load Next Descriptor Now) in UDPHS_DMACONTROLx register.
The structure that defines this transfer descriptor must be aligned.
Each buffer to be transferred must be described by a DMA Transfer descriptor (see “UDPHS DMA Channel Transfer
Descriptor” on page 564). Transfer descriptors are chained. Before executing transfer of the buffer, the UDPHS may
fetch a new transfer descriptor from the memory address pointed by the UDPHS_DMANXTDSCx register. Once the
transfer is complete, the transfer status is updated in the UDPHS_DMASTATUSx register.
To chain a new transfer descriptor with the current DMA transfer, the DMA channel must be stopped. To do so,
INTDIS_DMA and TXRDY may be set in the UDPHS_EPTCTLENBx register. It is also possible for the application to wait
for the completion of all transfers. In this case the LDNXT_DSC field in the last transfer descriptor
UDPHS_DMACONTROLx register must be set to 0 and CHANN_ENB set to 1.
Then the application can chain a new transfer descriptor.
The INTDIS_DMA can be used to stop the current DMA transfer if an enabled interrupt is triggered. This can be used to
stop DMA transfers in case of errors.
The application can be notified at the end of any buffer transfer (ENB_BUFFIT bit in the UDPHS_DMACONTROLx
register).
Figure 32-9. Data IN Transfer for Endpoint with One Bank
USB Bus
Packets
FIFO
Content
TX_COMPLT Flag
(UDPHS_EPTSTAx)
TXRDY
Flag
(UDPHS_EPTSTAx)
Prevous Data IN TX Microcontroller Loads Data in FIFO Data is Sent on USB Bus
Interrupt Pending
Set by firmware Cleared by hardware Set by the firmware Cleared by hardware
Interrupt Pending
Cleared by firmware
DPR access by firmware DPR access by hardware
Cleared by firmware
Payload in FIFO
Set by hardware
Data IN 2Token IN NAKACKData IN 1Token IN Token IN ACK
Data IN 1 Load in progress Data IN 2