Re: [Xenomai] s3c24xx: Priority rotate enable !?

[Romain Naour <romain.naour@openwide.fr>]

Le 23/08/2012 10:07, Gilles Chanteperdrix a écrit :
> On 08/22/2012 06:21 PM, Gilles Chanteperdrix wrote:
>> On 08/22/2012 06:04 PM, Romain Naour wrote:
>>> Hello,
>>>
>>> On s3c24xx processors the interrupt source priority isn't fixed by Adeos
>>> patch (ARB_SEL bits in PRIORITY register).
>>> Is it intentional ?
>>> It may be possible to give priority to an interrupt simultaneously
>>> arrived that the interruption IRQ_TIMER4 (before being grabbed by
>>> Adeos). Therefore, we can have more jitter for real time applications.
>> This can always happen even with interrupt priorities: imagine that the
>> first interrupt happens 1 microsecond before the timer interrupt, even
>> with the priority, the handler for first interrupt will be executed and
>> the timer interrupt will have to wait for the end of this handler before
>> it is serviced.
>>
>>> Do we need to fix the priority at this level ?
>> I do not think so. However, what can be done is implement interrupt
>> controller muting using the priority register, see:
>> http://www.xenomai.org/index.php/I-pipe-core:ArmPorting#Priority_based_interrupt_controller_muting
The priority register can't be used for implement interrupt controller 
muting using this method .
The PIC hardware can't be configured with only two priority levels.
We are obligated to choose between fixed or "rotation fashion" priority 
with 32 levels...

However, we can try to implement interrupt controller muting using 
bit-mask method.
But, bits mask are scattered between 4 registers:
32 bits in INTMSK (IRQ 16 to 47)
20 bits in EINTMASK (IRQ 48 to 67)
2 bits in LCDINTMSK (IRQ 68 and 69)
15 bits in INTSUBMSK (IRQ 70 to 84)
Fortunately there are only 69 interrupts.

> Other things which could be done for s3c24xx are:
> - convert the timers to clocksource/clockevent: since this platform is
> the only one not to use clocksource/clockevent, we have to keep code
> around for this case in xenomai-forge which could be removed. Having two
> different timers for clocksource and clockevent would allow to avoid the
> tsc emulation based on the decrementer, which I am not sure is really
> reliable since the conversion to CONFIG_IPIPE_ARM_KUSER_TSC.
> - failing that, check that the tsc emulation based on the decrementer
> really works, and maybe fix it if it does not work. Or simply use a
> different hardware timer for tsc emulation than for the timer.
>
I used Xenomai 2.6.0 with kernel 2.6.38.8 on mini2440 board during my 
internship.
I haven't seen bug with tsc emulation.

Xenomai-forge will not work on s3c24xx since it needs 
CONFIG_GENERIC_CLOCKEVENTS.

Regards,
Romain