SPI SD Card, sharing same instance with another peripherals

[Miguel Roque]

Hi all,

I'm recently working with Nordic devices (more precisely nRF52840), so I'm still learning. I'm working on a project where I have a shared SPI bus with several devices (each with its own CS pin), and one of them is a SD Card. Initially, to validate the hardware I make use of the available SD Card library from the Nordic SDK, and it worked like a charm (only the SD Card). However, now I have to deal with the fact that I have other peripherals (sensors mainly) that also make use of the same SPI pins.

On our projects, our sensor drivers accept an external SPI instance (created on Main) and then, internally the driver controls the CS in a blocking way. And that works for all the peripherals that make use of the same SPI instance, basically it works in a synchronous way.

However I noticed that the SDK SD Card library doesn't accept that procedure, due to the fact that it creates internally its own SPI instance and deals with it in an asynchronous way. How can I solve it? Does anyone faced the same problem? I'm trying to interact with fatfs directly, but with no success until the moment...

Thanks in advance by your time!!

Miguel Roque

[EDIT: I had to reopen this thread because accidentality I closed the other post :( ]

[Miguel Roque]

BTW, I'm using the "sdcard" library available on SDK (together with the "fatfs example()"). The SPI instance is created inside app_sdcard.c and is created in accordance with a SPI handler (that uses to deal with the sd card operation). So it doesn't even admits to pass as argument an external SPI instance.

[dejans]

Hi Miguel,

Are you using nRF5 SDK or nRF Connect SDK?

Best regards,

Dejan

[Miguel Roque]

Hello Dejan,

Thank you for your support, I did implement it. In addition I declared the SPI instance created by the sdcard library as extern and used on my main for the other sensors. However I still have no success, the sdcard indeed is initialized, however when I try to initialize my sensors (making use of the same SPI instance form sdcard), I cant make a connection with the sensor...

Adding to your suggestions, I also changed the SPI handler function inside sdcard library in way to ignore any SPI actions that were not originated by the library its own. 

Also, looking to the SPI lines using a logic analyser, I noticed that the MISO line is maintained in high level after the sd card initialization. Based on MMC/SSD documenatition this might be normal for some SD Cards models, and to force the mmc/ssd card to be an HighZ we should send 8 clock pulses while holding the CS line high. I did that also, but still with no success...

Thats the situation point by now...

[dejans]

Hi,

Thank you for the update.

Could you share more information of the failing SPI communication after the SD card is initialized? 

Have you considered using two SPI instances instead of one?

You could also try using ~100ohm resistor between the SD card 's MISO pin and the SPI bus to limit the current sourcing from SD card to other SPI devices.

Best regards,

Dejan

[Miguel Roque]

Hello,

About the failing, I don't get an "error" lets say, simply the fact that the driver of my sensor reads just "0's". However, if I initialize the sensor driver without the sdcard, it works perfectly, so I assume that is something with the SPI instance that I use (created by the sdcard library) or is the sdcard it self that doesn't accept to run work in parallel.

I have considered that option... But for that I would need to initialize and deinitalize every time that I want to use either the sdcard or the sensors, that would be a bottleneck no?

I can try that, however is not so easy to implement, because I'm using an already produced design... but I will try it if the problem remains... Btw, I also configured the SPI on SDK config to use the MISO line as "pull-down", but with no differences...

I will keep you updated if any development arises.

Best regards,

Miguel Soares

[dejans]

Hi,

I would suggest you to try some of the options mentioned.

You can also keep me updated.

Best regards,

Dejan

[João Oliveira]

Hi Dejans,

I took over this development, and we were able to share the SPI instance by adapting the code in this repository and by adding a pull-up in the MISO line.

Now everything works flawlessly. Hope this information helps anybody trying the same thing as us.

Best regards,

João Oliveira