Peripheral DMA
UG0331 User Guide Revision 15.0
268
9.2.1.3
Timing and Control
The peripheral ready signals (for example, RxRDY and TxRDY in MMUART) from the SPI, MMUART,
COMM_BLK, and CAN are directly connected to the PDMA. The ready signals from the CAN are not
used and are tied to logic 1 internally. The PDMA takes care of writing or reading the receive or transmit
holding registers within each peripheral using the APB interface.
The DMAREADY_0 and DMAREADY_1 signals correspond to the ready signals from the fabric
peripheral. If the channel is configured for peripheral DMA and the direction is from the fabric peripheral
to memory, this signal indicates that the fabric peripheral can write data to memory. If the channel is
configured for peripheral DMA and the direction is from memory to the fabric peripheral, this signal
indicates that the fabric peripheral can read data from memory. The PDMA does not support peripheral to
peripheral data transfer, scatter-gather DMA, and I2C DMA.
9.2.1.4
Channel Arbiter
The channel arbiter is an arbitration algorithm used to service the channels based on the priority, as
shown in
page 265. By default, all channels have equal priority. To configure the PDMA
channel priority, RATIO_HIGH_LOW register must be configured by the AHB bus matrix master. The
RATIOHILO field in the RATIO_HIGH_LOW register indicates the ratio of high priority requests to low
priority requests. For example, a RATIOHILO value of 3:1 means that a high priority DMA channel has 3
DMA access opportunities for every one access of a low priority DMA channel.
When the RATIOHILO value is set to 0, both high and low priority requests are serviced in a round robin
fashion.
The following table lists the valid values for RATIOHILO. All other values are reserved.
Refer to
page 275 for more information on configuring the register.
9.2.2
Port List
Table 174 •
RATIOHILO Field Definition
Value
High:Low Ratio
Comments
0
Round robin
1
1:1
Ping-pong between high and low priority requests
3
3:1
3 high to 1 low
7
7:1
7 high to 1 low
15
15:1
15 high to 1 low
31
31:1
31 high to 1 low
63
63:1
63 high to 1 low
127
127:1
127 high to 1 low
255
255:1
255 high to 1 low
All others
Reserved
Table 175 •
Port List
Name
Type
Polarity Description
DMAREADY_FIC_0
Input
High
DMAREADY_FIC_0
Input
High
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