Datasheet

(USBHS_HSTPIPCFGx.PSIZE / USBHS_DEVEPTCFGx.EPSIZE) and the Buffer Byte Length
(USBHS_HSTDMACONTROLx.BUFF_LENGTH / USBHS_DEVDMACONTROLx.BUFF_LENGTH) fields.
The USBHS average throughput can reach nearly 480 Mbps. Its average access latency decreases as burst length
increases due to the zero wait-state side ef
fect of unchanged pipe/endpoint. Word access allows reducing the AHB
bandwidth required for the USB by four, as compared to native byte access. If at least 0 wait-state word burst
capability is also provided by the other DMA AHB bus slaves, each DMA AHB bus needs less than 60% bandwidth
allocation for full USB bandwidth usage at 33 MHz, and less than 30% at 66 MHz.
Figure 39-24. Example of a DMA Chained List
Data Buffer 1
Data Buffer 2
Data Buffer 3
Memory Area
Transfer Descriptor
Next Descriptor Address
AHB Address
Control
Transfer Descriptor
Transfer Descriptor
USB DMA Channel X Registers
(Current Transfer Descriptor)
Next Descriptor Address
AHB Address
Control
NUL
L
Status
Next Descriptor Address
AHB Address
Control
Next Descriptor Address
AHB Address
Control
39.5.5 USB DMA Channel Transfer Descriptor
The DMA channel transfer descriptor is loaded from the memory. The following structures apply:
Offset 0:
• The address must be aligned: 0xXXXX0
• Next Descriptor Address Register: USBHS_xxxDMANXTDSCx
Offset 4:
• The address must be aligned: 0xXXXX4
• DMA Channelx Address Register: USBHS_xxxDMAADDRESSx
Offset 8:
• The address must be aligned: 0xXXXX8
• DMA Channelx Control Register: USBHS_xxxDMACONTROLx
To use the DMA channel transfer descriptor, fill the structures with the correct values (as described in the following
pages), then write directly in USBHS_xxxDMANXTDSCx the address of the descriptor to be used first.
Then write 1 in the USBHS_xxxDMACONTROLx.LDNXT_DSC bit (load next channel transfer descriptor). The
descriptor is automatically loaded upon pipe x / endpoint x request for packet transfer.
SAM E70/S70/V70/V71 Family
USB High-Speed Interface (USBHS)
© 2019 Microchip T
echnology Inc.
Datasheet
DS60001527D-page 773