[AT91SAM9260] kernel hang in at91sam926x_pit_reset()

[AT91SAM9260] kernel hang in at91sam926x_pit_reset()

[Vitja Makarov]

Hi!

I've recently found that our new AT91SAM9260 boards does not work with
linux out of the box.
The only thing changed is CPU revision now it is "Rev. B' (old boards
used "Rev. A" CPUs)


So after uncompressing kernel it writes. "Booting kernel..." that's
all. Kernel hangs.

I found that it hangs in  at91sam926x_time.c:at91sam926x_pit_reset():

Bit in AT91_PIT_PIVR register never clears... so I add timeout for
this loop and kernel boots as expected.

static void at91sam926x_pit_reset(void)
{
<------>/* Disable timer and irqs */
<------>at91_sys_write(AT91_PIT_MR, 0);

<------>/* Clear any pending interrupts, wait for PIT to stop counting */
<------>while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
<------><------>cpu_relax();

<------>/* Start PIT but don't enable IRQ */
<------>at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
}


Thanks,
vitja.

[AT91SAM9260] kernel hang in at91sam926x_pit_reset()

[Alexander Stein]

On Thursday 11 November 2010, 12:41:48 Vitja Makarov wrote:
> Hi!
> 
> I've recently found that our new AT91SAM9260 boards does not work with
> linux out of the box.
> The only thing changed is CPU revision now it is "Rev. B' (old boards
> used "Rev. A" CPUs)
> 
> 
> So after uncompressing kernel it writes. "Booting kernel..." that's
> all. Kernel hangs.
> 
> I found that it hangs in  at91sam926x_time.c:at91sam926x_pit_reset():
> 
> Bit in AT91_PIT_PIVR register never clears... so I add timeout for
> this loop and kernel boots as expected.
> 
> static void at91sam926x_pit_reset(void)
> {
> <------>/* Disable timer and irqs */
> <------>at91_sys_write(AT91_PIT_MR, 0);
> 
> <------>/* Clear any pending interrupts, wait for PIT to stop counting */
> <------>while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
> <------><------>cpu_relax();
> 
> <------>/* Start PIT but don't enable IRQ */
> <------>at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
> }

This won't work as you cannot set PIT_PITEN until the PIT has stopped 
(UserManuel 17.3), read as CPIV is 0. You should check if and why CPIV isn't 
increasing.

Best regards
Alexander

[AT91SAM9260] kernel hang in at91sam926x_pit_reset()

[Vitja Makarov]

2010/11/11 Alexander Stein <alexander.stein@systec-electronic.com>:
> On Thursday 11 November 2010, 12:41:48 Vitja Makarov wrote:
>> Hi!
>>
>> I've recently found that our new AT91SAM9260 boards does not work with
>> linux out of the box.
>> The only thing changed is CPU revision now it is "Rev. B' (old boards
>> used "Rev. A" CPUs)
>>
>>
>> So after uncompressing kernel it writes. "Booting kernel..." that's
>> all. Kernel hangs.
>>
>> I found that it hangs in ?at91sam926x_time.c:at91sam926x_pit_reset():
>>
>> Bit in AT91_PIT_PIVR register never clears... so I add timeout for
>> this loop and kernel boots as expected.
>>
>> static void at91sam926x_pit_reset(void)
>> {
>> <------>/* Disable timer and irqs */
>> <------>at91_sys_write(AT91_PIT_MR, 0);
>>
>> <------>/* Clear any pending interrupts, wait for PIT to stop counting */
>> <------>while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
>> <------><------>cpu_relax();
>>
>> <------>/* Start PIT but don't enable IRQ */
>> <------>at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
>> }
>
> This won't work as you cannot set PIT_PITEN until the PIT has stopped
> (UserManuel 17.3), read as CPIV is 0. You should check if and why CPIV isn't
> increasing.
>
> Best regards
> Alexander
>

Could it be hardware bug? With revision A it works. Do you have
success on use rev B. CPUs?
May be the problem is in u-boot or initial loader?

[AT91SAM9260] kernel hang in at91sam926x_pit_reset()

[Alexander Stein]

On Thursday 11 November 2010, 13:50:12 Vitja Makarov wrote:
> > This won't work as you cannot set PIT_PITEN until the PIT has stopped
> > (UserManuel 17.3), read as CPIV is 0. You should check if and why CPIV
> > isn't increasing.
> > 
> > Best regards
> > Alexander
> 
> Could it be hardware bug? With revision A it works. Do you have
> success on use rev B. CPUs?
> May be the problem is in u-boot or initial loader?

We don't use 9260 actually, we use the successor 9g20. Have you read the 
errata ? And yes, it could be a problem in u-boot or your other loader.
But AFAIK u-boot uses the PIT as a free running timer to get a time base.

Best regards,
Alexander