How to stop a circular DMA at end of buffer

[Kuikui]

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

[waclawek.jan]

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

[Zt Liu]

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

[Kuikui]

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.