Atmel Xplained Evaluation Board AT32UC3A3-XPLD AT32UC3A3-XPLD 데이터 시트
제품 코드
AT32UC3A3-XPLD
660
32072H–AVR32–10/2012
AT32UC3A3
27.7.4
USB DMA Operation
27.7.4.1
Introduction
USB packets of any length may be transferred when required by the USBB. These transfers
always feature sequential addressing. These two characteristics mean that in case of high
USBB throughput, both HSB ports will benefit from “incrementing burst of unspecified length”
since the average access latency of HSB slaves can then be reduced.
always feature sequential addressing. These two characteristics mean that in case of high
USBB throughput, both HSB ports will benefit from “incrementing burst of unspecified length”
since the average access latency of HSB slaves can then be reduced.
The DMA uses word “incrementing burst of unspecified length” of up to 256 beats for both data
transfers and channel descriptor loading. A burst may last on the HSB busses for the duration of
a whole USB packet transfer, unless otherwise broken by the HSB arbitration or the HSB 1kbyte
boundary crossing.
transfers and channel descriptor loading. A burst may last on the HSB busses for the duration of
a whole USB packet transfer, unless otherwise broken by the HSB arbitration or the HSB 1kbyte
boundary crossing.
Packet data HSB bursts may be locked on a DMA buffer basis for drastic overall HSB bus band-
width performance boost with paged memories. This is because these memories row (or bank)
changes, which are very clock-cycle consuming, will then likely not occur or occur once instead
of dozens of times during a single big USB packet DMA transfer in case other HSB masters
address the memory. This means up to 128 words single cycle unbroken HSB bursts for bulk
pipes/endpoints and 256 words single cycle unbroken bursts for isochronous pipes/endpoints.
This maximal burst length is then controlled by the lowest programmed USB pipe/endpoint size
(PSIZE/EPSIZE) and the Channel Byte Length (CHBYTELENGTH) field in the Device DMA
Channel n Control (UDDMAnCONTROL) register.
width performance boost with paged memories. This is because these memories row (or bank)
changes, which are very clock-cycle consuming, will then likely not occur or occur once instead
of dozens of times during a single big USB packet DMA transfer in case other HSB masters
address the memory. This means up to 128 words single cycle unbroken HSB bursts for bulk
pipes/endpoints and 256 words single cycle unbroken bursts for isochronous pipes/endpoints.
This maximal burst length is then controlled by the lowest programmed USB pipe/endpoint size
(PSIZE/EPSIZE) and the Channel Byte Length (CHBYTELENGTH) field in the Device DMA
Channel n Control (UDDMAnCONTROL) register.
The USBB average throughput may be up to nearly 53 Mbyte/s. Its average access latency
decreases as burst length increases due to the zero wait-state side effect of unchanged
pipe/endpoint. Word access allows reducing the HSB bandwidth required for the USB by four
compared to native byte access. If at least 0 wait-state word burst capability is also provided by
the other DMA HSB bus slaves, each of both DMA HSB busses need less than 60% bandwidth
allocation for full USB bandwidth usage at 33MHz, and less than 30% at 66MHz.
decreases as burst length increases due to the zero wait-state side effect of unchanged
pipe/endpoint. Word access allows reducing the HSB bandwidth required for the USB by four
compared to native byte access. If at least 0 wait-state word burst capability is also provided by
the other DMA HSB bus slaves, each of both DMA HSB busses need less than 60% bandwidth
allocation for full USB bandwidth usage at 33MHz, and less than 30% at 66MHz.