Associate III

Question

How to stop a circular DMA at end of buffer

3 replies
2448 views

Posted on May 24, 2017 at 18:59

Hi,

I'm using an STM32F446.

I use the circular DMA feature with a DAC output to generate a sinus waveform.

My sinus buffer has 32 values.

What I would like to do is :

- run the DMA for a 'large' amount of time

- be able to stop the DMA when I want, but only at end of buffer (so that the latest data sent to the DAC output is known and fixed).

I tried to change the 'circular mode' to 'normal mode' while the DMA is running (supposing the DMA would continue until end of buffer), but it doesn't work.

I know one of the way is to run in 'normal mode' and use the 'HALF-DMA' interrupt, but I would like to avoid this because it increases CPU load due to the interrupt.

Any idea ?

Thanks for help.

#dac-dma-circular-buffer

DAC

This topic has been closed for replies.

Super User

Posted on May 25, 2017 at 01:44

Don't know of any trivial way, except simply giving the transfer-complete interrupt a high enough priority and stop it at that moment.

Other way may be to stop the source of DMA trigger, again precisely enough in time.

JW

Senior III

Posted on May 25, 2017 at 10:32

Hey, VDM, I am free this afternoon!

Just using Cube MX to generate a little project to test your requirement.

You can download the attached project to see if it's really whatyou need !

(using STM32F446 Nucleo board)

The dma setting is still in circular mode. Using TIM2's update event to trigger dac.

As to stop the dac only in the end of buffering,

I implemented aDAC_OFFRequest flag and a dac dma call backHAL_DAC_ConvCpltCallbackCh1.

Every time the 32 data are transferred , this callback is called. And IFthe turn off flag is set, the callback function will stop the dac.

I also use LD2(PA5) pin to trigger the oscilloscope. Toggle high as a DAC_OffRequest is set.

________________

Attachments :

DAC_DMA_SINE.rar : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006Hyao&d=%2Fa%2F0X0000000bAS%2FYCgk_N4FuAiFwD1jV98z71M0UQyeWmTz73VpTElrDME&asPdf=false

KuikuiAuthor

Associate III

Posted on May 25, 2017 at 12:18

Thanks

Liu.Zhitai

I'm not used to Cube MX, I'm that kind of guy that mostly works 'from scratch', but it seems your answer is the same as

Waclawek.Jan

‌ : just set a high priority IT at end of DMA transfer and stop it ASAP.

I'll try that, thank you for your answers.