Re: 6502 stack register at reset

From: Segher Boessenkool <*segher_at_kernel.crashing.org*> Date: Sat, 25 Nov 2017 16:27:55 -0600 Message-ID: <20171125222755.GN10515@gate.crashing.org> · segher_at_kernel.crashing.org

On Sat, Nov 25, 2017 at 03:32:06PM -0600, Segher Boessenkool wrote:
> On Sat, Nov 25, 2017 at 08:50:21PM +0100, didier derny wrote:
> > Is there any 6502 starting with an initialized stack register at reset ?
> > 
> > a few month ago I was struggling with a strange bug...
> > 
> > the program was crashing or working randomly
> > 
> > I discovered that the machine had a stack register never initialized
> 
> That's right, see node 187: the "write" external signal is never asserted
> during a reset (so that the CPU will not do a "wild" write; the stack
> pointer isn't initialised).

That's node number in visual6502.  The transistor disabling the write on
resets is
http://www.visual6502.org/JSSim/expert.html?nosim=t&find=t3455&panx=391.4&pany=198.6&zoom=5.0

Segher

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