NRF52811-QCAA-R7 datasheet(36/444 Pages) NORDIC

36 / 444 page

Core components

An EasyDMA channel is implemented in the following way, but some variations may occur:

READERBUFFER_SIZE 5

WRITERBUFFER_SIZE 6

uint8_t readerBuffer[READERBUFFER_SIZE] __at__ 0x20000000;

uint8_t writerBuffer[WRITERBUFFER_SIZE] __at__ 0x20000005;

// Configuring the READER channel

MYPERIPHERAL->READER.MAXCNT = READERBUFFER_SIZE;

MYPERIPHERAL->READER.PTR = &readerBuffer;

// Configure the WRITER channel

MYPERIPHERAL->WRITER.MAXCNT = WRITEERBUFFER_SIZE;

MYPERIPHERAL->WRITER.PTR = &writerBuffer;

This example shows a peripheral called MYPERIPHERAL that implements two EasyDMA channels - one for

reading called READER, and one for writing called WRITER. When the peripheral is started, it is assumed

that the peripheral will:

• Read 5 bytes from the readerBuffer located in RAM at address 0x20000000.

• Process the data.

• Write no more than 6 bytes back to the writerBuffer located in RAM at address 0x20000005.

The memory layout of these buffers is illustrated in EasyDMA memory layout on page 36.

readerBuffer[0]

readerBuffer[1]

readerBuffer[2]

readerBuffer[3]

readerBuffer[4]

writerBuffer[0]

writerBuffer[1]

writerBuffer[2]

writerBuffer[3]

writerBuffer[4]

writerBuffer[5]

0x20000000

0x20000004

0x20000008

Figure 5: EasyDMA memory layout

The WRITER.MAXCNT register should not be specified larger than the actual size of the buffer

(writerBuffer). Otherwise, the channel would overflow the writerBuffer.

Once an EasyDMA transfer is completed, the AMOUNT register can be read by the CPU to see how many

bytes were transferred. For example, CPU can read MYPERIPHERAL->WRITER.AMOUNT register to see how

many bytes WRITER wrote to RAM.

Note that the PTR register of a READER or WRITER must point to a valid memory region before use. The

reset value of a PTR register is not guaranteed to point to valid memory. See Memory on page 16 for

more information about the different memory regions and EasyDMA connectivity.

4.6.1 EasyDMA error handling

Some errors may occur during DMA handling.

If READER.PTR or WRITER.PTR is not pointing to a valid memory region, an EasyDMA transfer may result

in a HardFault or RAM corruption. See Memory on page 16 for more information about the different

memory regions.

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