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Why does booting Linux on iMX7D A7 stop operation of M4 running out of QSPI?

Question asked by Jeremy McClintock on Jun 5, 2018
Latest reply on Nov 14, 2018 by Jeremy McClintock

On the iMX7D Sabre board we are able to launch an M4 application from UBOOT which is running exclusively out of TCM and then launch Linux (running in DDR) on the A7 without issue (both cores run as expected without interruption).  If we link the M4 application to execute out QSPI, and launch it from UBOOT, it runs OK until we proceed to boot Linux.  Once the "Starting Kernel" message appears on the A7 console, the M4 stops executing.


I have looked through the KCONFIG and DTS files and do not see any obvious reason why the A7 booting Linux stops the M4's execution in this scenario?  Any thoughts or insights would be appreciated.  Also, the application note AN5317 does not address starting M4 QSPI based applications, it is only directly applicable to RAM based applications.  Even though the steps should be the same, Linux does not seem to have access to the 0x60000000 address space by default, and I cannot find the configuration/DTS settings to enable this.