DMA_InitTypeDef explanation

[Alexandre T]

Posted on October 13, 2017 at 18:02

Can someone explain me how to use the 'PeriphInc' in the DMA_InitTypeDef.

I understood that it can read several address (is that right ?), but where I write the start and end adress ?

[Amel NASRI]

Posted on October 13, 2017 at 19:04

Hi

alexandre.julien

‌,

Taking the example of STM32CubeF7, I checked the

http://www.st.com/content/ccc/resource/technical/document/user_manual/45/27/9c/32/76/57/48/b9/DM001897pdf/files/DM001897pdf/jcr:content/translations/en.DM001897pdf

(Description of STM32F7 HAL and Low-layer drivers) where I found following description (p275):

uint32_t DMA_InitTypeDef::PeriphInc Specifies whether the Peripheral address register should be incremented or not. This parameter can be a value of DMA_Peripheral_incremented_mode

Please refer to the description of this structure in order to know more about all the fields.

-Amel

[Alexandre T]

Posted on October 13, 2017 at 20:26

Yes I already read it but in fact, I don't understand what it means. Does it means that I can do multiple reads on several address ? If so, how can I write the start and end adress ?

[Tesla DeLorean]

Posted on October 13, 2017 at 21:12

You define the direction of the transfer, and the length in transfer units.

You specify the source and destination addresses using HAL_DMA_Start(), which is the peripheral depends on the direction. It will be the source address in the 'from peripheral' case.

[Alexandre T]

Posted on October 13, 2017 at 21:24

Sorry but I still don't get it. 

For example :

If I want to do multiple reads (I have an accelerometer and I want to read x,y,z values),

Do I need to configure several DMA or is it possible to do it with only one ?

[Tesla DeLorean · Accepted solution]

Posted on October 13, 2017 at 21:44

It is pretty simple, but they both need to be within the addressable space of the processor.

An SPI based peripheral is going to get accessed by repetitive reads of &SPI1->DR, an address that ISN'T incrementing.

If the registers in the accelerometer are 16-bit and there are 3 of them, you'd program the DMA to transfer 6-bytes, and you'd be dependent on the external device to 'auto increment' its internal register address.

[Alexandre T]

Posted on October 13, 2017 at 21:52

Thank you, that's the answer I was waiting for !