Hi Jared Evans,
do you mean you got the assert as below?

if you have a NULL req, that might mean you didn't define a right SDHC request, please refer to the KSDK API RM, 61.12.3 SDHC Issuing a request to the card, for details.
BTW, The coming KSDK 2.0 has updated fatfs and freertos as well, and it also provides a bare metal sdcard_fatfs demo for FRDM-K64F board, so maybe you can use this demo as a starting point for your application when ksdk 2.0 is available.
Have a great day,
Kan
NXP Technical Support
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