DFSDM 8 serial channels but 4 filters. Why????

[delphi]

Posted on June 11, 2016 at 20:44

I use the DFSDM in multichannel sound card USB. It is 1st time for me.

I have read that the average DFSDM has 8 channels.When I started the project I have found that STM engineers added only 4 filters for 8 channels. It is incredible. I can't understand why? For exmaple I bought several boards and want to create 8 channel PDM MEMS mic sound card. I have introduced in MEMSIC board and found 4 channel example. I wanted to increase the number of channels. I found near the 5 bugs and correct it. So now I can create it in hardware. But during the introduction in filters I found that it is difficult to make this without integrated filters approach as it be in 4 channel example. Could you help me to understand how can I do that for 8 channels using only 4 digital filters. Or maybe I am wrong? #dfsdm

[delphi]

Posted on June 13, 2016 at 09:38The code of example for MEMSMIC is extemely unclear. For exmaple i want to disable the filter and use the raw pcm data. I can't even find the way and the good info for DFSDM libary. 

[delphi]

Posted on June 14, 2016 at 14:35

5 days and no answers. The best support as I've ever seen.

This answer is very critical part of MCU marketing. It seems that ST engineers must help me if the company is interested in market success. Many potential customers can decide to choose  another platform if they find this not replied message and understand that they cann't do real good quality multichannel usb devices.

[AvaTar]

Posted on June 14, 2016 at 14:56

> 5 days and no answers. The best support as I've ever seen.

Well, this is an e2e forum, mostly carried by customers and users of STM32 controllers.> This answer is very critical part of MCU marketing. > It seems that ST engineers must help me if the company is interested in market success. Approaching a ST representative or FAE directly seems more appropriate in your case. Albeit ST staff is monitoring this forum, they are definitely not the main contributor.

[delphi]

Posted on June 14, 2016 at 18:40

Could anybody help me to get the raw data from DFSDM using DMA for each channel. Am I understand right that using CHDATINR is a right way?

[delphi]

Posted on June 14, 2016 at 18:54

It seems that there is no possbility to get raw data from DFSDM using DMA. I can't find in DFSDM_Channel_TypeDef anything for DMA handler. WTF? 

[Tesla DeLorean]

Posted on June 14, 2016 at 18:59

Sorry, not in my area of interest, which is why I didn't reply originally.

If you want support from ST you need to go in via classic channels, the engineers and FAEs don't work via social media channels. Find the sales, support, or distribution channels local to you. Use ''Online Support'' rather than the forum.

http://www.st.com/content/st_com/en/support.html

http://www.st.com/content/st_com/en/contact-us.html?sc=salesoffices

[delphi]

Posted on June 15, 2016 at 09:43

I created a ticket. But has no answer yet.

It seems that the getting raw data using dma from DFSDM is not possible.If so then the DFSDM in STM32 will never use all 8 channels simultaneusly. If so then the STM32 made a huge mistake in crystal architecture and marketings broshures lie about the real possbilities of cortex M4. Only 4 channel can be used under signal processing. I want everybody know that fact!

[AvaTar]

Posted on June 15, 2016 at 10:10

Like Clive, this is not my specific field of interest, so I didn't consider posting at first.

The reference manual ('en.DM00224583.pdf', for the STM32F76xxx and STM32F77xxx) says at chapter 17.1, page 505:Digital filter for sigma delta modulators (DFSDM) is a high-performance module dedicated to interface external Σ�? modulators to a microcontroller. It is featuring up to

8

external digital serial interfaces (channels) and up to

4

digital filters with flexible Sigma Delta stream digital processing options to offer up to 24-bit final ADC resolution. ...DFSDM module supports the connection of up to

8

multiplexed input digital serial channels which are shared with up to

4

DFSDM modules. Might you have misinterpreted this ?

[delphi]

Posted on June 15, 2016 at 12:20

May be half of channels is useless in this case?

May be filter must be only filter and there is a way to use the raw data?Maybe each channel of DFSDM must contain the integrator even? But I see that the integrator is also at filter. Then the filter for DFSDM is not only filter but contains the integrator wich destroys the term ''Interface for sigma-delta modulator'', which must integrate EACH channel but not half of channels?Or maybe CUBE MX HAL is a piece of shit if this tool don't provide such method?