topic Re: facing issue with assembly instruction mtmsr in PowerQUICC Processors

facing issue with assembly instruction mtmsr

lakshmanank — Mon, 15 Jul 2013 11:02:21 GMT

Hi All

I am facing some issue with mtmsr assembly instruction while trying to write into msr register of MPC8641D.

below is my code which is compiling successfully but get runtime error as illegal instruction.

asm ("mfmsr %0;"

: "=r" (fromMSR) // output operand

);

printf("after mfmsr");

asm("mtmsr %0;"

: "r" (toMSR) // input operand

);

printf(" after mtmsr");

Output:

after mfmsr

illegal instruction -- error

what could be the possible error in the above code?

is the syntax is correct?
c

Re: facing issue with assembly instruction mtmsr

marius_grigoras — Mon, 15 Jul 2013 11:20:03 GMT

Hi,

Please find below an example about using mtmsr instruction with MW compiler from CW Classic:

asm void __reset(void)

{

// Enable altivec, floating point and machine check exception

lis r3, 0x0200

ori r3, r3, 0x3000

mtmsr r3

b __start

}

What toolchain/compiler are you using? Can you tell me please also your CW version?

Regards and thank you,

Marius

Re: facing issue with assembly instruction mtmsr

hwrobel — Mon, 15 Jul 2013 11:52:25 GMT

Your code looks as if it is Linux user space.

mtmsr is a privileged instruction. A Linux user process is not allowed to mess with mtmsr directly. This is for the kernel.

Heinz

Re: facing issue with assembly instruction mtmsr

lakshmanank — Tue, 16 Jul 2013 03:03:28 GMT

Hi Marius

I am using Buildroot cross compiler for MP8641HPCN architecture.

I am not using any Code Warrior. I am just building an userspace application and trying

in my board loaded with linux.

Hi Heinz

Thanks for your reply. So You mean I dont have any write access from userspace to change the MSR.

Is my understanding correct??

Thank you

Lachu

Re: facing issue with assembly instruction mtmsr

hwrobel — Tue, 16 Jul 2013 05:08:40 GMT

Correct. You can’t execute privileged instructions in user mode. Check, e.g., the e600 documentation and the Power ISA 2.06 for details.

Re: facing issue with assembly instruction mtmsr

lakshmanank — Wed, 17 Jul 2013 05:53:23 GMT

Hi Heinz

As you told me I understood that I cannot use msmtr instruction in userspace. I am now writing the msr register in uboot initialization and verifying what I have written. I am trying to write an application to run on uboot. prior to that I tried running the hello_world demo example in uboot. I am facing issue with loads command. after going through some web sources I understood it may be a problem in load address.

Now I want to know how should I separate the application from compiling along with uboot so that i dont want to compile uboot everytime I want to compile my application.

or do we have any other replacement to wrtie into MSR and other special purpose registers in userspace application(using movw instruction).

Regards

Lakshmanan K