We are developing a piece of software which sends low-level commands to the 
eMMC device in order to access certain special features of the chip. MMC 
writes and reads are typically a sequence of commands (CMD8, CMD23, etc.).

Often, it seems that our sequence of commands is being interrupted by the 
OS which does some logging, which is also to the MMC device (our rootfs). 
During the interruptions, data are written (and maybe read), which gets our 
own command sequence out-of-sync, including taking the device out of 
"command" mode.

We have confirmed that if we boot from the SD card (and not the eMMC) we do 
not have this problem; presumably, the logging happens independently to the 
SD card, and our own read/writes to MMC are fine. Unfortunately, this is 
not a viable long-term solution.

So, the question is: how can our program temporarily seize control of the 
MMC device? Can we temporarily halt OS disk activity? Make our program 
uninterruptible?

Thank you!

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