
ADSP-BF59x Blackfin Processor Hardware Reference
5-41
Direct Memory Access
• How heavily is the DMA controller competing with the core for
on-chip and off-chip resources?
• How often do competing DMA channels require the bus systems to
alter direction?
• How often do competing DMA or core accesses cause the SDRAM
to open different pages?
• Is there a way to distribute DMA requests nicely over time?
A key feature of the DMA architecture is the separation of the activity on
the DMA access bus (DAB) used by the peripherals from the activity on
the buses between the DMA and memory. For DMA to/from on-chip
memory the DMA core bus (DCB) is used, and the DMA external bus
(DEB) is used for DMA transfers with off-chip memory. The “Chip Bus
Hierarchy” chapter explains the bus architecture.
Each peripheral DMA channel has its own data FIFO which lies between
the DAB bus and the memory buses. These FIFOs automatically prefetch
data from memory for transmission and buffer received data for later
memory writes. This allows the peripheral to be granted a DMA transfer
with very low latency compared to the total latency of a pipelined memory
access, permitting the repeat rate (bandwidth) of each DMA channel to be
as fast as possible.
DMA Throughput
Each peripheral DMA channel has a maximum transfer rate of one 16-bit
word per two system clocks in either direction. Like the DAB and DEB
buses, the DMA controller resides in the
SCLK
domain. The controller syn-
chronizes accesses to and from the DCB bus, which runs at the
CCLK
rate.
Each memory DMA channel has a maximum transfer rate of one 16-bit
word per system clock (
SCLK
) cycle.
Содержание ADSP-BF59x Blackfin
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