readl writel: how do they work?

Mario Raffin

There are two executables readl and writel which can be used to write arm register on linux (I am working with DM365 and montavista).

I wonder how these work in the user space since they don't need an external module to be loaded, maybe there is an internal module already available.

I am going to write a kernel module but the existence of these two functions make me suppose that maybe there is already something I can use.

Maybe they use the memory mapped register opening the /dev/mem ? Is it possible to have some more detail, or possibly the souce code of the two functions?

Thank you.

over 13 years ago

0 Prabhakar Lad over 13 years ago

Guru 11260 points

Hi Peregrinus,

There are two executables readl and writel which can be used to write arm register on linux (I am working with DM365 and montavista).

I wonder how these work in the user space since they don't need an external module to be loaded, maybe there is an internal module already available.

I am going to write a kernel module but the existence of these two functions make me suppose that maybe there is already something I can use.

Maybe they use the memory mapped register opening the /dev/mem ? Is it possible to have some more detail, or possibly the souce code of the two functions?

Its not so difficult, as it looks to be, you need to open /dev/mem obtain the fd and MMAP the given address,

and perform read write depending on your need.

I have attached the source.5811.regreadwrite.c

Thx,

--Prabhakar Lad

0 Mario Raffin over 13 years ago in reply to Prabhakar Lad

Expert 2405 points

It works!!

As I suspected the solution was simpler than writing a device driver.

Thank you very much Prabhakar.

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readl writel: how do they work?