Intel® PXA27x Processor Family
Optimization Guide
3-17
System Level Optimization
3.5.3
Usage of DMA
The DMA controller is used by the PXA27x processor peripherals for data transfers between the
peripheral buffers and the memory (internal and external). Also, depending on the use cases and
user profiles, the operating system may use DMA for copying different pages for its own
operations.
shows DMA controller performance data.
Proper DMA controller usage can reduce the workload of the processor by allowing the Intel
XScale® core to use the DMA controller to perform peripheral I/O. The DMA can also be used to
populate the internal memory from the capture interface or external memory, etc.
3.5.4
Peripheral Bus Split Transactions
The DMA bridge between the peripheral bus and the system bus normally performs split
transactions for all operations. This allows for some decoupling of the address and data phases of
transactions and generally improves efficiency. This can be disabled and requires active
transactions complete before another transaction starts. Please refer to the DMA Programmed I/O
Control Status register described in the
Intel® PXA27x Processor Family Developer’s Manual
for
detailed information on this feature and its usage.
Note:
When using split transactions (default): If software requires that a write complete on the peripheral
bus before continuing, then software must write the address, then immediately read the same
address. This guarantees that the address has been updated before letting the core continue
execution. The user must perform this read-after-write transaction to ensure the processor is in a
correct state before the core continues execution.
Table 3-7.
Memory to Memory Performance Using DMA for Different Memories and
Frequencies
Clock Ratios
†
DMA Throughput for
Internal to Internal
Memory
DMA Throughput for
Internal to External
Memory
104:104:104
127.3
52.9
208:104:104
127.6
52.3
195:195:97.5
238.2
70.9
338:169:84.5
206
59.4
390:195:97.5
237.9
68.6
†
Ratio = Core Frequency : System Bus Frequency : Memory Bus Frequency
Summary of Contents for PXA270
Page 1: ...Order Number 280004 001 Intel PXA27x Processor Family Optimization Guide April 2004...
Page 10: ...x Intel PXA27x Processor Family Optimization Guide Contents...
Page 20: ...1 10 Intel PXA27x Processor Family Optimization Guide Introduction...
Page 30: ...2 10 Intel PXA27x Processor Family Optimization Guide Microarchitecture Overview...
Page 48: ...3 18 Intel PXA27x Processor Family Optimization Guide System Level Optimization...
Page 114: ...5 16 Intel PXA27x Processor Family Optimization Guide High Level Language Optimization...
Page 122: ...6 8 Intel PXA27x Processor Family Optimization Guide Power Optimization...
Page 143: ...Intel PXA27x Processor Family Optimization Guide Index 5 Index...
Page 144: ......
