SD/SDIO/MMC Host Controller IP regarding

[sampathpb]

mmc modes

Hi Friends,
My question is regarding the SD/SDIO/MMC Host Controller IP core features.

I know that the SD card and MMC cards (upto Ver4.2) support the SPI mode of operation, in addition to the primary protocol ., ie SD protocol and MMC protocol.

My understanding of the reason for providing support for SPI mode in the memory cards is that, they can be used in conjunction with the off-the-shelf microcontrollers, that do not currently have support for SD or MMC protocol.
By this, these cards be used in designs where the SD/MMC protocol is still not implemented, but has SPI readily available.

Now, I was refering to some of the IP vendors where the SD/SDIO/MMC host controller provides (in addition to 1-bit and 4-bit SD), the SPI mode of operation.

I donot understand why the host IP core should support the SPI mode ? Since the host IP already implements SD protocol , it will connect to the card through SD mode itself. And as I understand, there is no memory card, that implements only SPI without SD or MMC modes.

So, why in some Host IP core, they are mentioning that SPI mode as one of the modes of operation ?

thanks in advance,
best regards,
sampathpb

 

[frankvh]

sd controller

SPI mode is a required item in the MMC/SD specification. Therefore, for a controller to be in full compliance with the spec, it has to implement it. If they don't, they can't claim full compliance and it would limit their ability to sell their product.

You're correct in saying you may choose not to use that function. But they still feel the need to provide it.

Frank.
https://www.frankvh.com

 

[sampathpb]

sd mmc controller

Hi Frank,
thanks for your reply,
So, what you are saying is that, the host controller IP should be able to connect to the SD/MMC memory cards using both the SD protocol and SPI protocol ?
I am wondering about the benifit of trying to connect these two using more than one means (SD / SPI).

Yes, I agree, the SD memory card itself should support both the modes (by this, it can be used in designs where you have the SD protocol and in designs where you dont have SD protocol (like microcontrollers that supports spi mode).

But I really dont understand why there should be more than one communication channel to connect between Host controller IP and SD memory card.

regards,
sampath