Adding Zynq platform support to base-hw

[Martin Stein]

Hi Johannes,

Sorry for answering that late. I had overlooked your mail.

Unfortunately the newest qemu version available for my system is 2.0.0
so there might be differences in our observations. After modifying your
qemu config from "-m 1024" to "-m 256" I get serial output from the
beginning of 'init_kernel_up' till
'Sctlr::write(Sctlr::init_virt_kernel());' in 'init_kernel_mp ->
Cpu::init_virt_kernel'. So this seems to be a problem with enabling the MMU.

You could do single-step at this point and check the IP after the write
to the SCTLR to see in which exception vector you end up (see
base-hw/src/core/spec/arm_v7/mode_transition.s: _mt_kernel_entry_pic). I
assume it to be either _dab_entry or _pab_entry. If this is the case,
reading the ARM registers DFSR/DFAR respectively IFSR might help to
track down the cause.

One known problem that arises when enabling the MMU is that this also
enables ARM caches and branch predictors. You can try deactivating them
for test purpose.

'Z::set(v, 0);' in 'Sctlr::init_virt_kernel' in
'base-hw/src/core/include/spec/arm_v7/cpu_support.h' and an empty
'Arm_v7::inval_branch_predicts' method should disable branch predictors.

Should 'C::set(v, 0);' and 'I::set(v, 0);' in 'Sctlr::init_common' in
'base-hw/src/core/include/spec/arm/cpu_support.h' and adapted TEX/C/B
fields in the 'CACHED' case in 'Translation::_create' in
'base-hw/src/core/include/spec/arm/short_translation_table.h' should
disable ARM caches.

You might also check wether your UART and your Core image are mapped
correctly 1:1 by instrumenting the translation-table methods.

Cheers,
Martin

On 15.12.2014 19:43, Johannes Schlatow wrote:
> Hey,
>
> I just started adding support for the Zynq SoC to base-hw (see [1]).
>
> As I don't have any Zynq hardware available yet, I tried running this
> on QEMU 2.1.2; I compiled the run/hw_info target.
>
> After applying some printf debugging ;), I figured out that the program
> dies (i.e. QEMU freezes) during kernel initialisation
> in init_virt_kernel(). I therefore tried attaching gdb to QEMU's
> internal gdb server, however, it seems to ignore my breakpoints.
>
> Hence my question: Do you guys have any experience with low-level/kernel
> debugging on QEMU? Maybe I am missing something or QEMU is just weird?
>
> [1]
> https://github.com/ValiValpas/genode/commit/4e375384d635d06626f0b226ac14e21f608d717a
>
> Cheers
>  Johannes
>
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