Re: [Openocd-development] How to disable MMU in OpenOCD?

[Dominic <Dom...@gm...>]

On Friday 05 September 2008 11:17:15 Øyvind Harboe wrote:
> 2008/9/5 dswei <ds...@si...>:
> > Thank you, vind_Harboe.
> > I don't exactly know what is "srst_pulls_trst" 's mean, but I can disable
> > MMU now, that is enough for my urgent task now.
>
> Would you care to check the datasheets?
>
> Basically some CPUs have, internally, srst tied to trst. This makes it
> impossible
> to reset the CPU without also resetting the embedded ice registers, making
> reset directly into the halted mode impossible.
>
> > I run the openocd command "arm920t cp15 2 0",  "step", "poll", then the
> > MMU is diabled. But now I have another question:
> > 1. The "help cp15" is:
> > arm920t cp15i        display/modify cp15 (interpreted access) <opcode>
> >                          [value] [address]
> > arm920t cp15        display/modify cp15 register <num> [value]
> >
> > 2. the format of  ARM instruction mcr and mrc are:
> >
> > MCR/MRC{cond} P15,opcode_1,Rd,CRn,CRm,opcode_2
> >
> > 31    28  27 26 25 24   23      21 20  19     16 15    12  11 10 9 8    7
> >        5   4   3        0
> >
> > | Cond | 1   1   1   0 | opcode1 | L |    CRn  |    Rd    | 1  1  1  1 |
> > | opcode2 | 1 |   CRm  |
> >
> > What is the relation beteen "arm920t cp15" and ARM instruction mcr and
> > mrc? I try "arm920t cp15 0", "arm920t cp15 1", "arm920t cp15 2", and so
> > on, to read the cp15; and then know that "arm920t cp15 2" is for MMU. Are
> > there some exact relations between "MCR/MRC{cond}
> > P15,opcode_1,Rd,CRn,CRm,opcode_2" and "arm920t cp15", ""arm920t cp15i"?
>
> Could you investigate and post an explanation?

Check the ARM920t TRM - only certain combinations are possible, and they're 
all listed in the TRM.

Regards,

Dominic