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Renesas Electronics America - Knowledgebase

RZ/T1 Important Notes for the Thumb Instruction Set

Last Updated:09/27/2017


Are there any important notes in regards to using the Thumb instruction set?


The Cortex-R4 architecture is supposed to set the CPU operation mode to ARM instruction mode when an interrupt occurs after coming from a reset.
Therefore, it's not possible to make a program using only the Thumb instruction set – even if you want to.  In other words, you must make a program using both the ARM instruction set and the Thumb instruction set.

With that, make certain to follow these two points:

- Implement the exception vectors using ARM instructions.

- Implement the FIQ/IRQ interrupt handler using ARM instructions. 

Depending on your tool environment, they could be implemented with C source code declaring a dedicated specifier for an interrupt function.

As reference, please refer to our sample program "RZ/T1 Group Initial Settings (r01an2554)" on our web site.

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