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RL-ARM: switching to User- instead of System mode

Information in this knowledgebase article applies to:

  • Keil MDK 4.53 or older,  with RTX until 4.60


I have just seen that even though I start running in System mode, after returning from os_sys_init(), the RTX is moving to User mode. I was expecting it still should be at System Mode.

Why is this happening?


The RTX version in use needs to be at least V4.60 (after June 2012) in order to not change to User mode.

Check for the version in the map file(__RL_RTX_VER). A line like this one refers to RTX version V4.13:

__RTX_ARM_VER   EQU     0x413


Either use at least RTX version V4.60 or install at least Keil MDK 4.54.

Then the RTX should leave the processor running in System mode if System mode was active before calling os_sys_init().


Last Reviewed: Thursday, October 22, 2020

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