topic Re: Difference between "fnop" and "nop" assembly instructions in CodeWarrior Development Tools

Difference between "fnop" and "nop" assembly instructions

xuedongyang — Thu, 13 Jan 2022 16:18:45 GMT

Hi, experts,

I am wondering what is the difference between "fnop" and "nop" assembly instructions. I am referring the document "VSPA-16SP ISA-v3.0 Instruction Set Manual for LA1224, Rev. A 10/2019". I see "fnop" and "nop" instructions in the document, but do not know the difference between them.

I tried both instructions in an assembly function I am working on. It seems to me both instructions work.

Thanks,

Xuedong Yang

Re: Difference between "fnop" and "nop" assembly instructions

yipingwang — Mon, 17 Jan 2022 06:06:46 GMT

The ‘fnop’ is always a full 64-bit instruction. It can be useful for aligning code.

With ‘nop’ the compiler can choose either a 32-bit instruction or a 64-bit instruction.

The VSPA ISM revision that you are referring to (RevA) is quite old. In the later revisions of the ISM it was decided to replace all fnop to nop, and publish only nop in the document so as to give more flexibility to the compiler.

I believe Rev 0 is the VSPA ISM latest revision available for LA1224. Do you have access to the latest rev?

Re: Difference between "fnop" and "nop" assembly instructions

xuedongyang — Mon, 17 Jan 2022 13:32:18 GMT

Thanks, Yiping, for the helpful answer.

No, I don't have latest version of LA1224 ISM, and don't know how to get it.

It would be great if you could guide me how to get the latest version of the document.

Re: Difference between "fnop" and "nop" assembly instructions

yipingwang — Fri, 21 Jan 2022 03:41:22 GMT

Please refer to the attached document.

Re: Difference between "fnop" and "nop" assembly instructions

xuedongyang — Fri, 21 Jan 2022 03:50:50 GMT

Thank you very much for providing the latest document.