How to sync EDMA3 "ping" (vs pong) buffer transfer with my code - Processors forum - Processors

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MikeH

Guru 15580 points

I am using the EDMA3 LLD to create a ping-pong buffered transfer to and from the McASP which is sending & receiving audio data to/from the AIC3204 codec. On the path that sends an audio stream *to* the codec (let's call it "receive" in this example since I am receiving a data stream from a remote, non-synchronized source) I am having difficulties synchronizing the data that is buffered in my code with the proper (ping or pong) EDMA3 transfer to the McASP. As you know, the purpose of the ping-pong buffer is to allow you to continue filling one buffer while the other buffer is being DMA'd to the McASP for transmission to the codec output. However, when the buffered data is ready for the EDMA transfer to the McASP I do not know whether the EDMA is expecting to send the ping, or the pong buffer. Is there a way to determine which transfer the EDMA is expecting? The EDMA code is essentially the audio example code from the BIOS training lab, which uses a linked ParamSet with reload. Here is the text from the lab.

2. For a sync'd ping/pong transfer, we need 6 PSETs. Two are our active channels

// (one for RCV and one for XMT). The RCV side uses the McBSP DRR as the source

// and gBufferRcv as the destination. The XMT side uses gBufferXmt as the source

// and the McBSP DXR register as its destination. The other 4 PSETs are used for

// linking ping and pong. The active channels are set as "ping" and are linked to

// the pong reload PSETs. The pong reload PSET is linked back to ping. Hence,

// we have two active channels and 4 reload PSETs.

Any creative ideas on how to determine ping vs pong would be much appreciated.

Thx

MikeH

over 14 years ago

0 MikeH over 14 years ago

Guru 15580 points

Wow. It's amazing how sometimes when you explain a problem to others, you see it more clearly. I solved this problem!

The essence of the issue is that, the McASP *requires* a constant, uninterrupted stream of data in order to prevent underflow of it's XRBUF. Therefore, the ping and pong buffers *must* remain in sync from the start of the program or else you'll get an underrun. Therefore, you *must* service the EDMA callback interrupt each and every time it happens or you will underrun. Therefore, if you *do* service the interrupt you will always remain in sync with the ping-pong swap. This means the McASP is essentially "pulling" the data from my buffer when it needs it, instead of me pushing the data into the ping-pong buffer when it is available. Subtle, but important.

I hope this helps someone else think this problem through.

Thx,

MikeH

0 shivanand mishra over 12 years ago

Prodigy 10 points

I am using the EDMA3 with ping-pong bufferring to receive and transfer the audio data. The data is received through codec to ASP to EDMA3 ping pong buffers.

Now I have to process the received data by using MELP analysis to generate 54 voice parameters (to be transmitted at 2.4kbps) for 180 received samples.

sampling rate = 8kbps, 16 bits data, frame lenth = 180= ping pong buffers size

The MELP analysis of received voice data is taking 15 ms time and the buffer size is 22.5ms.

Now those 54 bits have to be transmitted through ASP McBSP to codec.

THE PROBLEM WHAT I FACED IS data is getting missed. So pls suggest me appropriate register setting of DM6446 processor on CCS3.3.