base-hw ,,, What is CACHE_LINE_SIZE_LOG2?

[Martin Stein]

Hi Bob,

The only purpose of the parameter CACHE_LINE_SIZE_LOG2 is to enable us
flushing the level 1 data cache of ARM in base-hw selectively. It
controls the granularity of the flushing commands and is set correctly
only for the Arndale board by now. The value "2" is the least possible
value for ARM and slows flushing in the worst case while a value that
would be higher than the correct value might cause data incoherence.
Long story short: you can use "2" if you don't find the correct value in
the level-1-cache description of your board spec.

Do you know which revision of Cortex-A8 (r1p1..r3p2) your board uses?
Maybe there are quirks in your revision that base-hw doesn't support by now.

Have you checked whether the mappings you're adding to core TLB cover
the text and BSS segment of the bin/core image?

You can also deactivate caches temporarily by initializing
Arm::Cpu::Sctlr::C and Arm::Cpu::Sctlr::I in Arm::Cpu::Sctlr::common
with 0 (base-hw/src/core/cpu/arm.h). This would at least limit the
candidates.

PS: there is an open issue "base-hw crashes without caches" but as long
as you're not above core/init this shouldn't affect you.

Cheers,
Martin

On 15.11.2013 18:16, bob wrote:
> Hi,
>      Is CACHE_LINE_SIZE_LOG2 the line length in 32 bit words of the L2 
> Instruction or Data caches? That's the only cache line length I see in 
> the board spec of the am335x in its TRM.
>
> I'm having a problem the initial start of the kernel, which appear to 
> hang when the MMU is switched on in init_virt_kernel function. The tlb 
> should set up correctly as I've defined the boards physical ram and MMIO 
> regions in the Core_tbl class. The CACHE_LINE_SIZE_LOG2 parameter 
> appears to be used as the stride length for walking the tlb. It is 
> currently set at 2 only because that's the value used in the Panda and 
> imx53 boards board_base.h. If that's not the problem, I'm at a loss as 
> to what the issue could be since the CPU object is straight cortex-a8 
> from the arm_v7 architecture. Any pointers to how to diagnose the issue 
> would be a great help.
>
> Thanks,
>
>          Bob Stewart
>
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