Look at the AN3659 for SPI boot:
https://www.nxp.com/docs/en/application-note/AN3659.pdf?fsrch=1&sr=1&pageNum=1
Look at also attached file. This file is available in LTIB Linux BSP for the MPC8309SOM:
https://www.nxp.com/webapp/sps/download/license.jsp?colCode=MPC8309-KIT_Linux_BSP
Have a great day,
Pavel Chubakov
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