StarterWare 1.20.04.01 McASP Example without EDMA

Hi, i'm trying McASP on c6748 LCDK with XDS100v2.

The loopback example of McASP from StarterWare can work.

In the example, the EDMA with ping-pong operation transfers/receives the buffers.

But I want to apply adaptive echo cancellation, data by data, for the real-time processing.

I'm trying two ways now

1. Reduce the sizes of buffers

I've tried to make NUM_SAMPLES_PER_AUDIO_BUF as 2 (one data for two channel)

And play the 1kHz sine wave which is produced by the code below:

short y1[3] = {0, -11585 , -16384};
const short A1 = 23170;

y1[0] = (short)(((int)y1[1]*A1 + ROUND )>> 14) - y1[2];
y1[2] = y1[1];
y1[1] = y1[0];

But I don't know why the txbuffer is always 0.

2. Delete the API of EDMA and configure the McASP without EDMA

Did anyone have this kinds of experences?

It has bothered me two weeks. Please help me.