Peripheral DMA
UG0331 User Guide Revision 15.0
270
CHANNEL_x_CONTROL register should be set to 0 (peripheral to memory) and the PERIPHERAL_SEL
field should be set to 4 (SPI_0 receive to memory).
9.2.4.2
Posted APB Writes
The AHB to APB bridges in the SmartFusion2 device implement posted writes (also known as dump and
run) for write accesses to peripherals. PDMA performs a write operation to a peripheral but the data is
not written to the peripheral immediately. Therefore, the PDMA block should not start another DMA on
this channel based on the state of the ready signal from that peripheral until the write is complete. The
time window involved is variable, depending on the ratio of M3_CLK to PCLK, for each of the two
peripheral buses. WRITE_ADJ in the
register is an 8-bit binary coded field
used to define, for each DMA channel, how long to wait (in M3_CLKs) after each DMA transfer cycle
before interpreting the ready signal for that DMA channel as representing a new request.
A suitable value for WRITE_ADJ depends on the target of the DMA transfer.
The following steps describe how to select the values:
1.
The WRITE_ADJ value of 10 can be provided as a default value
•
When the PDMA channel is configured for transfers with MSS peripherals.
•
For DMA transfers with FPGA fabric implemented peripherals, making use of the DMAREADY0
or DMAREADY1 fabric interface signals indicate that the peripheral is ready for another DMA
transfer.
2.
The WRITE_ADJ parameter can be set to zero to achieve the maximum transfer speed for memory
to memory transfers.
3.
The internal latency of FPGA implemented peripherals decide the WRITE_ADJ value for fabric
peripherals that do not use the DMAREADY0 or DMAREADY1 fabric interface signals.
Содержание SmartFusion2 MSS
Страница 1: ...UG0331 User Guide SmartFusion2 Microcontroller Subsystem ...
Страница 166: ...Cortex M3 Processor Reference Material UG0331 User Guide Revision 15 0 132 ...
Страница 200: ...Embedded NVM eNVM Controllers UG0331 User Guide Revision 15 0 166 Figure 87 System Builder Window ...
Страница 407: ...Universal Serial Bus OTG Controller UG0331 User Guide Revision 15 0 373 ...
Страница 806: ...Fabric Interface Controller UG0331 User Guide Revision 15 0 772 Figure 345 FIC Master AHB Lite Subsystem ...