topic Re: Difference Between e_lwz and lwz in CodeWarrior Development Tools

Difference Between e_lwz and lwz

tektronix — Tue, 17 Dec 2013 16:03:32 GMT

What is the difference between e_lwz and lwz ? e_stw and stw? Apart from one is VLE and other is not? I see huge timing difference when I read or write to memory when using e_stw and stw.

Why is this so?

Regard's

Re: Difference Between e_lwz and lwz

Jorge_Gonzalez — Fri, 20 Dec 2013 03:28:21 GMT

Hello:

Could you please provide more details so your question can be investigated?

What software and device are you using?

What are those e_lwz and lwz you refer to?

Sorry about the questions, I'm just trying to help.

Regards!

Jorge Gonzalez

Re: Difference Between e_lwz and lwz

tektronix — Sun, 05 Jan 2014 03:09:45 GMT

I am using MPC56XX device and I am using CodeWarrior. I think they are based on VLE or non VLE

Re: Difference Between e_lwz and lwz

Jorge_Gonzalez — Mon, 06 Jan 2014 15:59:17 GMT

Hello:

Ok, thanks for sharing that information. I do not have an answer. We can wait for a response or you can always submit a service request if this is critical for you.

Regards!

Jorge Gonzalez

Re: Difference Between e_lwz and lwz

stanish — Mon, 13 Jan 2014 01:04:38 GMT

Hi,

indeed e_ prefix represents 32-bit VLE instrction whereas no prefix means BookE instruction.

Regarding e_stw / stw:

both are 32 bit instructions with same operands but different opcodes.I don't think there should be a big timing difference between these two instructions.

In general you can expect VLE code a bit slower in contrast to BookE but on the other hand the code density is much higher.

The higher code density may result in more efficient instruction cache/instruction buffer usage which may improve the code speed too.

Can you describe your observations more in the detail and also test case you use for benchmarking?

Thanks!

Stan