SDCARD in SD Card Mode, SPI mode and Maximum speeds?

[OwainIncus]

Has anyone used SDCard interface with either 52840 or 5340 in anything other than SPI mode?


I just noticed in the SDK 15.3 code we are using SDCard is in SPI mode. Seems max frequency being allowed is 8MHz; so that results in a pitiful data rate. ( <1MB/s raw interface speed?)
Elsewhere in this forum it is mentioned that one only gets the IP necessary to run in 4bit SD card mode if one signs up to SD Card Alliance; is this true?


I also see in the SDcard alliance base physical layer spec for SPI mode; that if one uses a card in SPI mode it is only guaranteed/good for class 0; so what speed is that if class 2 is 2MB/s, class 10 is 10MB/s???

What are options to get better external memory speeds; with scards?

QuadSPI (chips seem size limited), Nand interface?
Ideally I would like to stick with sdcards as cheap/ubiqitous.

Regards,
Owain

[Carl Richard]

Hello, Owain!

Apologies for the somewhat late answer here. I will try to answer your questions clearly:

- You are indeed limited to 8MHz speed on the normal SPI peripherals. However, the nRF5340 does boast a fourth SPI peripheral with support of 32MHz speeds. 
- From what I can see this is true. Non of our devices supports 4-bit SD Card interfacing, so I believe this would be difficult to utilize anyway.
- I think you can find better answers for this elsewhere, but based on what I could find the speed in SPI mode maxes out at about 40 MHZ.
- Our QSPI peripheral only supports NOR type flash. 

I think your best option for higher speeds if you want to use SDCards is to use the nRF5340 high speed SPI.

Best regards,
Carl Richard