This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Accessing CP14 from user mode

Note: This was originally posted on 9th July 2009 at http://forums.arm.com

Hello,

I'm currently trying to change the frequency of a PXA270 processor, the system I'm working on is a Linux OS, and I would like to write a code that allows an user to change the frequency, to do so I need to write in a register of coprocessor 14. According to ARM documentation i need to use MRC/MCR instructions, I tried but I got an error : "Illegal instruction".

So I think I need to switch to supervisor mode, it seems that I could do it using SWI but even after reading some documentation I don't know how I should implement this.
I'm not even sure that what I want to do is possible, but if it is, does someone have any idea of the code I should write to switch to supervisor mode and use MRC or MCR instruction?

Thanks,

Parents

kuan po huang over 12 years ago

Note: This was originally posted on 5th August 2009 at http://forums.arm.com

hi,

if you can modify kernel source, here is an option:

add system calls to read/write coprocessors

there are many tutorials about adding system calls in embedded linux kernel

embedded Linux kernel takes short time to build

googling "add system call" should help

thanks

Kuan-Po Huang

High Performance Computing Lab.
CSIE, National Chung Cheng University, Taiwan
[url="http://hpc.cs.ccu.edu.tw/"]http://hpc.cs.ccu.edu.tw/[/url]
Cancel
Vote up 0 Vote down

Cancel

Reply

kuan po huang over 12 years ago

Note: This was originally posted on 5th August 2009 at http://forums.arm.com

hi,

if you can modify kernel source, here is an option:

add system calls to read/write coprocessors

there are many tutorials about adding system calls in embedded linux kernel

embedded Linux kernel takes short time to build

googling "add system call" should help

thanks

Kuan-Po Huang

High Performance Computing Lab.
CSIE, National Chung Cheng University, Taiwan
[url="http://hpc.cs.ccu.edu.tw/"]http://hpc.cs.ccu.edu.tw/[/url]
Cancel
Vote up 0 Vote down

Cancel

Children

No data