Hi Aditya,
The booting information is in chapter 8 of Reference Manual. There you will find what you need about the boot process.
Regarding your question, SPL is not changing when you change the booting source, it is the fuses that you must configure.
When the imx boot, the romcode will run on first instance, it will read the fuses and will look for te boot source depending on the fuses configuration.
Regards,
Carlos
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