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Can an eMMC connected to USDHC1 be used as a boot device?

Hello,

I am checking the Boot ROM behavior of the i.MX 8DualX/8DualXPlus/8QuadXPlus family.

According to the reference manual, the recommended boot connections appear to be:

eMMC on USDHC0
SD/eSD/SDXC on USDHC1

However, in Figure 5-17, “Expansion device (SD/eSD/SDXC) boot flow”, when SD initialization fails, the flow continues through connector 2 to the MMC initialization flow in Figure 5-16. It appears that the ROM tries the MMC protocol on the same USDHC interface after the SD protocol fails.

Does this mean that an eMMC connected to USDHC1 can be detected and used as a Boot ROM boot device, possibly in 4-bit mode?

Or is this MMC fallback path intended only for protocol detection, while eMMC boot from USDHC1 is not officially supported?

I would also like to confirm whether the ROM switches from USDHC1 to USDHC0 at this point, or whether it continues using the same USDHC1 interface.

Thank you.

Re: Can an eMMC connected to USDHC1 be used as a boot device?

I am trying to understand the boot flow of the i.MX 8DualX/8DualXPlus/8QuadXPlus Boot ROM, especially for SD boot.

My current understanding is as follows.

After Primary and Secondary Boot fail, the ROM may enter SD/MMC Manufacture Mode, which is described as Recovery Boot.

In this mode:

The ROM scans SD or MMC devices on USDHC1.
A 1-bit data bus is used, regardless of the normal bus-width eFuse setting.
If a valid boot image is found, it is loaded and executed.

If an eMMC device is connected to USDHC1 and BOOT_MODE[3:0] is set to 0011 (SD boot through USDHC1), is the expected boot sequence as follows?

The ROM first attempts the normal Primary Boot using the SD boot flow, but it fails.
The ROM then attempts Secondary Boot, which also fails.
The ROM enters the SD/MMC Manufacture Mode (Recovery Boot), detects the eMMC device on USDHC1 using the MMC protocol, and successfully boots from it.

In other words, with this hardware configuration, would the system be able to boot from the eMMC only during the Recovery/Manufacture Boot stage, rather than during the normal Primary or Secondary Boot stages?

Re: Can an eMMC connected to USDHC1 be used as a boot device?

Hello,

eMMC on USDHC1 cannot be treated as a boot device, the documented primary mapping is eMMC on USDHC0, SD on USDHC1.

The USDHC1 fallback/recovery behavior is used by SD/MMC manufacture mode. You can take a look in section 5.11 of reference manual.

Best regards.