NRF52810-QFAA-R datasheet(203/483 Pages) NORDIC

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Peripherals

( GPDM,default ) and the gain introduced by the microphone and acoustic path of his implementation (an

attenuation would translate into a negative gain), and adjust GAINL and GAINR by this amount. Assuming

that only the PDM module influences the gain, GAINL and GAINR must be set to -GPDM,default dB to achieve

the requirement.

With GPDM,default=3.2 dB, and as GAINL and GAINR are expressed in 0.5 dB steps, the closest value to

program would be 3.0 dB, which can be calculated as:

GAINL = GAINR = (DefaultGain - (2 * 3))

Remember to check that the resulting values programmed into GAINL and GAINR fall within MinGain and

MaxGain.

6.10.4 EasyDMA

Samples will be written directly to RAM, and EasyDMA must be configured accordingly.

The address pointer for the EasyDMA channel is set in SAMPLE.PTR register. If the destination address set

in SAMPLE.PTR is not pointing to the Data RAM region, an EasyDMA transfer may result in a HardFault or

RAM corruption. See Memory on page 15 for more information about the different memory regions.

DMA supports Stereo (Left+Right 16-bit samples) and Mono (Left only) data transfer, depending on setting

in the OPERATION field in the MODE register. The samples are stored little endian.

MODE.OPERATION

Bits per sample

Result stored per RAM

word

Physical RAM allocated

(32 bit words)

Result boundary indexes

in RAM

Note

Stereo

32 (2x16)

L+R

ceil(SAMPLE.MAXCNT/2) R0=[31:16]; L0=[15:0]

Default

Mono

2xL

ceil(SAMPLE.MAXCNT/2) L1=[31:16]; L0=[15:0]

Table 42: DMA sample storage

The destination buffer in RAM consists of one block, the size of which is set in SAMPLE.MAXCNT register.

Format is number of 16-bit samples. The physical RAM allocated is always:

(RAM allocation, in bytes) = SAMPLE.MAXCNT * 2;

(but the mapping of the samples depends on MODE.OPERATION.

If OPERATION=Stereo, RAM will contain a succession of Left and Right samples.

If OPERATION=Mono, RAM will contain a succession of mono samples.

For a given value of SAMPLE.MAXCNT, the buffer in RAM can contain half the stereo sampling time as

compared to the mono sampling time.

The PDM acquisition can be started by the START task, after the SAMPLE.PTR and SAMPLE.MAXCNT

registers have been written. When starting the module, it will take some time for the filters to start

outputting valid data. Transients from the PDM microphone itself may also occur. The first few samples

(typically around 50) might hence contain invalid values or transients. It is therefore advised to discard the

first few samples after a PDM start.

As soon as the STARTED event is received, the firmware can write the next SAMPLE.PTR value (this register

is double-buffered), to ensure continuous operation.

When the buffer in RAM is filled with samples, an END event is triggered. The firmware can start

processing the data in the buffer. Meanwhile, the PDM module starts acquiring data into the new buffer

pointed to by SAMPLE.PTR, and sends a new STARTED event, so that the firmware can update SAMPLE.PTR

to the next buffer address.

4430_161 v1.0

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