hexdumping /dev/mem

[Thomas Skibo]

> On Mar 16, 2015, at 1:00 PM, Matías Perret Cantoni <perretcantonim at gmail.com> wrote:
> 
> Hello!
> 
> I'm trying to read a 32 bit register of the System Level Control
> Registers of the ZedBoard (Zynq-7000 SoC) from a running FreeBSD. I
> thought that I could simply do it with hexdump(1) to avoid writing a
> driver since I only need to read it once. I've tried:
> 
> 
> #hexdump -s 0xF8000910 -n 4 /dev/mem
> 
> 
> and I get this message:
> 
> hexdump: /dev/mem: Invalid argument
> 
> 
> Reading some archives in this mailing list I've found that "the arm
> version of /dev/mem is not functionally equivalent to that of amd64 or
> i386.  Arm disallows access to non-DRAM addresses through /dev/mem”.

That’s correct.  /dev/mem only reads from memory not devices.

I always use kdb to peek/dump registers.  You have to translate the device addresses (use “show devmap” to see the mappings).

But, once you know the kernel virtual addresses of the registers, you might be able to hexdump them through /dev/kmem.  (I don’t have a Zedboard in front of me to try that.)

> 
> Is there any other way of doing this? Maybe the whole idea of using
> hexdump for this isn't really good.
> 
> 
> 
> Thanks in advance.
> Regards,
> Matias.
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-------
Thomas Skibo
thomasskibo at sbcglobal.net