AN3997

Application overview

Doc ID 022390 Rev 1

9/15

This application reads all wave files from the USB Key and displays only the .WAV files that

have the following format:

●

Audio format: PCM (an uncompressed wave data format in which each value

represents the amplitude of the signal at the time of sampling)

●

Sample rate: such 8000, 11025, 16000, 22050, 44100 Hz or 48000 Hz.

●

Bits per sample: 16 bits (audio sample data values are in the range [0-1024])

●

Number of channels: 2 (stereo)

The wave from the USB Key is parsed to detect the sample rate in order to configure the

I2S accordingly. When the play back begins the blue LED starts toggling.

The playback is managed with double buffering. A first buffer is used to store the wave data

retrieved from the USB Key, using the FatFs file system.

Once this buffer is filled:

●

The DMA sends its content to the I2S peripheral which transfers it to the external audio

codec DAC

●

The data from the USB key is stored in a second buffer

Then these two buffers are swapped indefinitely, till end of the playback process.

At any time, if the USB Key is disconnected from the DISCOVERY board, the blue LED is

off, the audio DAC is stopped and red LED goes on.

When the USB Key is reconnected again to the DISCOVERY board, the red LED goes off

and the last running application starts again.

2.3.2

Playback from internal Flash

In this demonstration, the wave file is stored in the internal Flash as a const array declared

in the audio_sample.c file.

After a reset, the playback application starts playing the wave stored in the internal Flash

after initializing the Audio DAC.

2.4

Audio record application

The flowchart in Figure 5 describes the recording application. It is based on a MEMS

microphone. Audio record is available only when USB key is selected as mass storage

media.