Hello,

I would like to use the DMA as a double buffer between two seperate arrays in memory. The datasheet says this is possible, but does not address how to do so. 

The buffers are in code as follows:

uint8 buf[256]; //Data buffer to hold the output from the 8 bit counter

uint8 buf2[256];//2nd buffer for double buffering 

Any ideas? I am basing my project off of the PSoC Sensei blog FIFO component.

http://www.cypress.com/?rID=46730

Can you explain me how it should work so that I can write a code snippet and give it to you?

Regards,

Kishore.

Kishore,

Thanks for the reply.

The idea here is that the DMA component will fill one memory buffer until it is full. Once that 1st buffer is full, the DMA stops filling the first buffer, and starts filling the second buffer. While the 2nd buffer is being filled, the DMA (possibly a second channel) sends the data from the 1st buffer to another location (some kind of communications interface such as USB or UART). After the 1st buffer is done filling, the 2nd buffer is written out to the comm. interface and the 1st buffer is filled.

Here is a quick summary:

State 1) -> 1st buffer NOT full

DMA filling buffer 1

buffer 2 left alone (CPU or another DMA moves/operates on the data)

State 2) -> 1st buffer full

buffer 1 left alone

DMA filling buffer 2

This then continues. I have been using the hardware FIFO component from PSoC Sensei. I hope this clarifies things. I wasn't sure if this would require multiple DMA channels, multiple transaction descriptors, or another mechanism.

Thanks,

DiodeDan

 Update:

I've been playing with this. I started using two TDs with one DMA channel. The TDs write to different buffers in memory. They are linked to each other in a loop.

This appears to be somewhat working.

Is this something that I should open a support case for?

Thanks,

DiodeDan

Yes it would be better if you create a Tech Support case for this with the explanation which you gave for Ping-Pong as it would require some time.

Regards,

Kishore.

See appnote AN52705 page 12 section "Example 5: Ping-Pong Buffer".

app note: www.cypress.com/?docID=38384 

dma webpage including app note link: http://www.cypress.com/?rID=37793

@Helmut

I fell into a similar trap, that thread you replied to is more than 1 year old. I really would enjoy a newer forum software that helps us contributors a bit (or byte) more.

Bob

 Bob,

Actually, I didn't fall into a trap.  I knew that post was old.  I just added the appnote reference for anyone else searching for info on double buffering, who found that old [effectively unanswered] post.