::: Area #157 (comp.sys.acorn.programmer)
Message: #38542 (Read 5 times, has 0 replies, 2088 bytes)
Date   : Mon Dec 21 06:30:03 1998
From   : Justin Fletcher of fidonet#2:254/27.2
To     : All
Subject: Re: StrongBS
Message-ID: <1c2ec9b748%Justin@helen.winsley.org>

In message <75jt47$h4$1@kings-cross.london.uk.eu.org>
    Philip Blundell <philb@gnu.org> wrote:

> In article <10d47bb748%Justin@helen.winsley.org>,
> Justin Fletcher  <gerph@thevillage.ndirect.co.uk> wrote:
> >In message <ab.eI4lUoP@yeti.microdata.de>
> >    WIMPy@yeti.microdata.de (Birger Harzenetter) wrote:
> >
> > > >  Bxi%
> > > > which we all know to be branch to address xi%, but on Ursula this
> > > > comes out as Branch eXtended to register i%. Which fails when i%>16
> > > > or causes nasty
> > > Wot?!!! You don't tell, BASIC's inline assembler got thumb aware, do
> > > you?!?
> >
> > I don't think it's a Thumb instruction; However, I know very little about
> > the workings of the MSR instruction which it expands to -
> >
> >  BX 0
> >=>
> >  MSR CPSR_c_x_s_f,R0  ; ARMv3 and later
>
> BX is a special branch instruction which has the side effect of either
> entering Thumb mode (if bit 0 of the argument was set) or entering ARM
> mode (if it was clear).  Its bit encoding is rather similar to MSR and
> this is probably what's confusing your assembler.

It's Darren Salt's disassembler, I think, and it is pretty old so I guess
that might explain it; the internal debugger correctly decodes it anyhow.
The only other thing of note is that the Debugger also has
Debugger_DisassembleThumb, but I've not had a RPC long enough to know if
that's new or not.

Thanks for the correction; I shall obviously have to research this a
little at some point :-)

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