Hi -
I have been trying to implement a simple project on an LPC55S69EVK, where I read in audio samples from .wav files on an sd card, and then send them out to the audio codec on the board using I2S DMA. I have attempted this by adapting the FatFS and the I2S_DMA examples included in the MCUXpresso SDK.
So far i have got something to playback; however there is a popping sound and I do not know what causes it.
The popping is very intermittent, but gets more frequent the shorter the pieces of data I transmit. (i.e., the length of "data" as shown in my code).
The relevant parts of my code are attached below.
As you can see from the code, I set up the initial transfer of the data in "StartSoundPlayback();" . Then in the main while loop, I read in another n bytes of data before the next TxCallback is triggered. And so on.
Many thanks in advance.
Rory
short data4[200];
//main code
....
StartSoundPlayback();
while (1)
{
if(flag==1)
{
}
else{
error = f_read(&g_fileObject1,&data, sizeof(data),&bytesRead);
s_TxTransfer.data = &data[0];
s_TxTransfer.dataSize = sizeof(data);
flag = 1;
}
}
}
static void StartSoundPlayback(void)
{
PRINTF("Setup looping playback of sine wave\r\n");
s_TxTransfer.data = &data[0];
s_TxTransfer.dataSize = sizeof(data);
//s_TxTransfer.data = &g_Music[0];
//s_TxTransfer.dataSize = sizeof(g_Music);
I2S_TxTransferCreateHandleDMA(DEMO_I2S_TX, &s_TxHandle, &s_DmaTxHandle, TxCallback, (void *)&s_TxTransfer);
/* need to queue two transmit buffers so when the first one
* finishes transfer, the other immediatelly starts */
I2S_TxTransferSendDMA(DEMO_I2S_TX, &s_TxHandle, s_TxTransfer);
I2S_TxTransferSendDMA(DEMO_I2S_TX, &s_TxHandle, s_TxTransfer);
}
//callback for data transmit
static void TxCallback(I2S_Type *base, i2s_dma_handle_t *handle, status_t completionStatus, void *userData)
{
//if (completionStatus == kStatus_I2S_BufferComplete)
//{
/* Enqueue the same original buffer all over again */
i2s_transfer_t *transfer = (i2s_transfer_t *)userData;
I2S_TxTransferSendDMA(base, handle, *transfer);
count = 0;
flag = 0;
// }
}
