I'm looking for a guide that describes porting Microblaze code to the ARM Cortex M3.

Just google search "cortex-m3 sample code", many examples for that.

Hope it can help you .

  - https://www.arm.com/files/pdf/CortexM3_Uni_Intro.pdf

Danny_GOWIN said:

Microblaze processor

You mean this: https://www.xilinx.com/products/design-tools/microblaze.html ?

The process is going to be much the same as porting code from any given architecture to any other architecture.

You will require:

• At least a working understanding of the "source" architecture (eg, Microblaze) and its toolchain;
• At least a working understanding of the "target" architecture (eg, Cortex-M3) and its toolchain;
• At least a working understanding of the code you are porting.

It makes life much easier if you have full working development environments for both the original application on its original target and your intended "target".

Depending on the application, it might be as easy to just start from scratch ...