Differentiating between CM33 and CM85 with preprocessor

[renesas-kyle-finch]

In a previous issue submitted to CMSIS 5, I was told that it was no longer advisable to use the arch defines like __ARM_ARCH_8M_MAIN__ and to instead use __ARM_ARCH.

But dumping preprocessor defines for CM33 and CM85 both yield the same __ARM_ARCH* defines:

// Using GCC 13.2
#define __ARM_ARCH 8
#define __ARM_ARCH_8M_MAIN__ 1
#define __ARM_ARCH_EXT_IDIV__ 1
#define __ARM_ARCH_ISA_THUMB 2
#define __ARM_ARCH_PROFILE 77

Note that GCC generates __ARM_ARCH_8M_MAIN__ for both CM33 and CM85.

LLVM 17 generates the same as GCC, with the exception that it generates __ARM_ARCH_8_1M_MAIN__ for CM85.

How should CM33 and CM85 be differentiated with the preprocessor?

[JonatanAntoni]

Hi @renesas-kyle-finch,

this seems still to be a shortcoming in GCC. According to ACLE one should be able to detect the architecture by looking to __ARM_ARCH, see https://developer.arm.com/documentation/101028/0012/5--Feature-test-macros.

I'll pass this on to our GCC experts.

[renesas-kyle-finch]

@JonatanAntoni thank you.

To be clear, both GCC and LLVM both produce __ARM_ARCH 8 for both CM33 and CM85. From the link you provided, I would expect that they would produce __ARM_ARCH 8 for CM33 and __ARM_ARCH 801 for CM85.

Does that match your expectations as well?

[renesas-kyle-finch]

From some more testing of CM85 with multiple toolchains, this is what I am seeing for __ARM_ARCH and __ARM_ARCH_xx__

Toolchain	__ARM_ARCH	__ARM_ARCH_xx__
GCC	8	__ARM_ARCH_8M_MAIN__
LLVM	8	__ARM_ARCH_8_1M_MAIN__
AC6	8	__ARM_ARCH_8_1M_MAIN__
IAR	801	__ARM_ARCH_8M_MAIN__

So it seems neither paradigm produces correct output across all of these toolchains.

[ReinhardKeil]

CMSIS contains the revision number of each core using these defines: https://arm-software.github.io/CMSIS_6/v6.0.0/Core/group__device__config.html

Even when a device vendor does not provide the exact revision of the implementation, the fallback ensures that this define exists:

• https://github.com/ARM-software/CMSIS_6/blob/main/CMSIS/Core/Include/core_cm85.h#L222
• https://github.com/ARM-software/CMSIS_5/blob/master/CMSIS/Core/Include/core_cm85.h#L201

This information is therefore less dependent on Compiler internal defines specified by ACLE and maybe easier to query.

#if defined (__CM85_REV)    // running on Cortex-M85
 ...

I hope this helps.

[renesas-kyle-finch]

I will give that a try.

As far as looking to the future, are the __ARM_ARCH and __ARM_ARCH_ISA_THUMB macros still the advised macros to use and what the compilers should be striving to produce?