memory problems on Fiasco porting

Tsai, Tung-Chieh tsaitungchieh at
Tue Feb 17 19:34:34 CET 2009

Dear Adam,

On Mon, Feb 16, 2009 at 6:41 PM, Adam Lackorzynski
<adam at> wrote:
> Hi,
> On Sat Feb 14, 2009 at 20:25:19 +0800, Tsai, Tung-Chieh wrote:
>> On Fri, Feb 13, 2009 at 5:32 AM, Adam Lackorzynski
>> <adam at> wrote:
>> > The the data abort happens it should end up in the page fault handler
>> > and further on make a page visible at 0xc0080000. Does this happen or
>> > not?
>> Yes, and then it would stuck between irq_handler() and
>> Timeslice_timeout::expired().
> Hmm, so after the page-fault happened it is properly resolved and after
> the page fault handling is done there is a page at 0xc0080000? I'm just
> asking because when the irq_handler is invoked this has not really
> anything to do with page-fault handling but probably is a timer
> interrupt. Of course this timer interrupt is executed in a specific
> context and might also access the same address range. Might it be any
> cache related thing? At which instruction is it stuck? Is there anything
> special?

After page fault handler, there's a page at 0xc0080000 ~ 0xc0081000.

Initially, I thought this data abort exception is an error...  Now I've
understood it's not a problem.

But after I skip these exception, it would stuck between irq_handler()
and Timeslice_timeout::expired(). I found that it is because in the while
loop of Timeout_q::do_timeouts(), traveling the queue Timeout_q::_q via
Timeout::_next would exceed  Timeout_q::Wakeup_queue_count.

I put an assertion on how many time this while loop is executed, and
this assertion would not fail when I run it on QEMU integratorcp
platform. After this assertion failed, entering jdb, jdb shows that sigma0
had been added to ready/present list.

Since timmer interrupt had been enabled before
Kernel_thread::init_workload(), I thought this error may be occur at the
first timer interrupt after sigma0 had been added to ready queue.

I would check cache & tlb relative part again. Currently, for cache & tlb
part, I write the following function for arm922t:

  * Mmu<Flush_area, Ram>::flush_cache()
      clean D cache(write back), invalidate I & D cache, drain write buffer
  * Mmu<Flush_area, Ram>::clean_dcache()
      clean D cache, , drain write buffer
  * Mmu<Flush_area, Ram>::flush_dcache()
      clean and invalidate D cache, , drain write buffer
  * Mem_unit::tlb_flush( void* va, unsigned long)
      I just flush whole tlb here, since arm922t looks not have any
      instruction to flush a specific tlb entry without knowing it's
      instruction tlb or data tlb.
  * The other functions of Mmu and Men_unit I doesn't mention are
  using codes of arm926/armv5.

Did I missing something ? Or is there any other possible direction ?
Any advice is appreciate. Thanks.

Best Regards,
Tsai, Tung-Chieh

More information about the l4-hackers mailing list