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What does it mean to say "ARM Cortex-M processors are entirey C programmable"?

Gopal Amlekar

Hi,

Being new to the fascinating ARM world, I am going through various documentation and reading material.

I read that the ARM Cortex-M processors (or I think it applies to all the Cortex processors) are entirely C programmable. This means that assembly code is not required for start-up code and for ISRs.

I am curious to find out what prohibits the earlier ARM processors (or even other architectures) to write the start-up code in C? Are these any specific instructions? One which I found was the WFI (Wait For Interrupt) which can't have an equivalent in C. But that is not a start-up or ISR instruction.

Thanks for your support !

Gopal

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    Hi Gopal-san,

    I think that it would mean the interrupt handler of Cortex-M could be written in the same way as normal C functions. Actually to use WFI, we should use the asm statement. By the way, almost all parts of a program can be written by C. For example, the interrupt vectors which are made by the C language array of pointer to ISRs are located into address 0 by the C linker. By conventional ARM architecture (e.g. ARM7), instructions are located at the interrupt (including reset) vectors, and it would be impossible to write the startup codes by C language.

    Best regards,
    Yasuhiko Koumoto.