Re: [microblaze-uclinux] Petalinux v0.10-rc1, bug found

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Jack,

jack-uclinux@xxxxxxxxxxxxx wrote:

> I am using Petalinux v0.10 rc1, using a Microblaze CPU on a Xilinx 
> ML401 board. Generally working very well, but I have found a bug 
> that prevents the CPU reset button working correctly.

Glad to hear it's working well for you.

> Before uClinux boots (e.g. in fs-boot and u-boot), the ML401 CPU 
> reset button works correctly. After uClinux boots, the reset button 
> causes the system to crash.
>
> This is because fs-boot has been partially overwritten by
> pingpong_vector_table() in
> petalinux-v0.10-rc1/software/uClinux-2.4.x/arch/microblaze/platform/Xilinx-ML401/machine.c

The intention of the pingpong code is to allow a soft-reset to work - 
when we copy the interrupt/exception vectors etc on early boot, the 
original memory contents are simply swapped with the vectors.  On a soft 
reboot, we repeat the process, so any prior bootlaoder etc down there 
should be untouched.

The issue you are seeing is coming from a hard reset (a button wired 
directly to the reset signal), so the kernel gets no chance to undo the 
pingpong process.

> When the interrupt vector table is replaced, memory addresses
> between 0x4 and 0x68 are overwritten with the vectors. The highest
> vector is dbtrap, which is installed at 0x60. Unfortunately, part of the
> fs-boot loader is at 0x50:
>
> (mb-objdump -d fs-boot/executable.elf)
>
> So when I press reset, fs-boot jumps to 0x50, falls through to 0x60,
> and then runs the kernel dbtrap routine. Perhaps part of fs-boot 
> could be moved to a higher address?

Well spotted.  Moving FS boot a bit higher is probably the best solution 
- unfortunately 0x50 is the default link location in EDK so we'll need 
to add a custom link script of link option to the HW reference design 
makefiles.

You've most likely sorted this out yourself, but an interim solution is 
to manually edit the start address of FS-boot in XPS.

I'll file a bug report and make sure it's fixed in the next release.

Thanks,

John
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