Interfacing (DSI, CSI, I2C, etc.) • Possible to boot from eMMC over SDIO on a custom Pi HAT?

Hi,

I have started to look into the possibility of creating a custom Pi HAT that will have eMMC for boot / storage. I plan to use the SDIO interface for the same. With this setup on the RPi 5, I will be able to better utilize the remaining space on the custom Pi HAT for some other interfaces instead of having a m.2 slot for a 2280 NVME SSD. This also leaves the PCIe interface free. I'd rather not use USB for boot / storage, even though there might be benefits in terms of transfer speeds. I am hoping that eMMC on SDIO will do as good as NVME on PCIe or an external SSD on USB 3.0 in terms of random r/w.

So far, I have come across the below information.

From the RP1 Peripherals draft:

Chapter 4. SDIO


and


Chapter 3.1.1 Function select

From the news introducing the RPi 5:

Now based off the information above, I have the following questions:

1. The RP1 Peripherals draft suggests the presence of 2 SDIO controllers. And the RPi 5 introduction news mentions a direct interface to the processor for the SD Card. Is there an SDIO interface that is unused by SD Card and WiFi-BT?
2. If so, is the SDIO0 interface on GPIO22 to GPIO27 the unused interface?
3. Can it be used to interface an eMMC?
4. If the eMMC can indeed be interfaced over SDIO, will I require to give up the use of SDIO for SD Card interface by any chance?
5. The features not supported lists "eMMC Boot Protocol". Can I boot off the eMMC?
6. Right now I think the support for RPi 5 secureboot isn't present, but in the future, could I possibly use secureboot with the eMMC?
7. On the eMMC, would I see random r/w speeds similar to NVME SSDs or external USB 3.0 SSDs?

Would really appreciate some help with these questions.

Thanks.

Statistics: Posted by pinominator — Mon Feb 12, 2024 11:27 am

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