I do not know this CPU, but it is common for digital chips to have
volatile registers that are copied from a non-volatile storage at boot-up.

FPGAs, Ethernet controllers (e.g. RTL8019AS), MCUs (PIC18F87J60), etc.
use this approach.

Perhaps the run-time register resides on an address and its content is
copied at boot-up from another register in a different address.

This way the configuration can be changed easily at run-time but it has
a programmable reset value that can be changed if necessary.


Cheers,

Isaac




Em 31/10/2015 19:05, Jahn escreveu:
>  Recently I started playing with a MIPS CPU( made by Broadcom). As far as=
 I know it allows=20
> to=20
>  use a Broadband Studio to communicate with that CPU.=20
>  That MIPS CPU has Read/Write registers. I can write to these registers a=
nd in the=20
> Broadband=20
>  studio I can see the new value was written. I can read the register ( fr=
om the Broadband=20
> Studio=20
>  program).=20
>  But if I restart mainboard, that uses the MIPS CPU, there is the previou=
s value before I=20
> changed=20
>  it.( like a factory reset ).=20
> =20
>  Do you think the Broadband studio only emulates those registers and I wr=
ite to not the real=20
>  registers?=20
> =20
>  I used a logic analyzer to check how the Broadband studio writes to regi=
sters.=20
>  It does write to CPU but the address is different than a documentation s=
ays.=20
>  For example=20
>  Address Offset =3D 32'h001a_00d8=20
>  Physical Address =3D 32'h101a_00d8=20
> =20
>  but I can not see that address during sniffing with a logic analyzer=20
>  Any idea?=20
>  Thanks=20
>



--=20
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