Re: [Qemu-devel] [PATCH RFC v20 3/8] target/avr: Add mechanism to check for active debugger connection

[Michael Rolnik]

Richard.

We use break instruction for testing. (Here
https://github.com/seharris/qemu-avr-tests/tree/master/instruction-tests).
Each test is a big list of small tests with a break between them. We run
the tests on HW and on QEMU then compare register after each break. If we
don't implement break the way Sarah suggested we have no way of testing.
What do you suggest?

Sent from my cell phone, please ignore typos

On Wed, Jun 5, 2019, 5:37 PM Richard Henderson <address@hidden>
wrote:

> On 6/5/19 2:20 AM, Michael Rolnik wrote:
> > Hi Richard.
> >
> > I am still struggling with this one.
> >
> > The spec says.
> > The BREAK instruction is used by the On-chip Debug system, and is
> normally not
> > used in the application software.
> > When the BREAK instruction is executed, the AVR CPU is set in the
> Stopped Mode.
> > This gives the On-chip Debugger access to internal resources.
> > If any Lock bits are set, or either the JTAGEN or OCDEN Fuses are
> unprogrammed,
> > the CPU will treat the BREAK instruction as a NOP and will not enter the
> > Stopped mode.
>
> Yep.
>
> > I read is as follows
> > - If user has an intention of using debugger, BREAK should be translated
> to
> > QEMU debug breakpoint
> > - If user has no intention of using debugger, BREAK should be translated
> into NOP.
>
> I do not read it that way.  The spec is talking about a specific
> implementation
> of debugging -- fuses, jtag and all.  We do not need to implement
> breakpoints
> using any of those mechanisms, because we can insert breakpoints via
> on-the-side data structures and re-translation.
>
>
> r~
>

On Wed, Jun 5, 2019, 5:37 PM Richard Henderson <address@hidden>
wrote:

> On 6/5/19 2:20 AM, Michael Rolnik wrote:
> > Hi Richard.
> >
> > I am still struggling with this one.
> >
> > The spec says.
> > The BREAK instruction is used by the On-chip Debug system, and is
> normally not
> > used in the application software.
> > When the BREAK instruction is executed, the AVR CPU is set in the
> Stopped Mode.
> > This gives the On-chip Debugger access to internal resources.
> > If any Lock bits are set, or either the JTAGEN or OCDEN Fuses are
> unprogrammed,
> > the CPU will treat the BREAK instruction as a NOP and will not enter the
> > Stopped mode.
>
> Yep.
>
> > I read is as follows
> > - If user has an intention of using debugger, BREAK should be translated
> to
> > QEMU debug breakpoint
> > - If user has no intention of using debugger, BREAK should be translated
> into NOP.
>
> I do not read it that way.  The spec is talking about a specific
> implementation
> of debugging -- fuses, jtag and all.  We do not need to implement
> breakpoints
> using any of those mechanisms, because we can insert breakpoints via
> on-the-side data structures and re-translation.
>
>
> r~
>