MMP2 Interrupt Controller forcing IRQ

[Andrei E. Warkentin]

Hi Chris, Mitch,

2011/9/26 Chris Ball <cjb at laptop.org>:
> Here's a transcription of an explanation Mitch just gave:
>
> It's certainly possible to route any given interrupt to either FIQ or
> IRQ on either core.  It is possible for an instruction to cause an
> interrupt/exception; that's how OFW does breakpoints.  At the CPU core
> level, each core has exactly one IRQ and one FIQ, for a total of 4.
> Each of the many hardware interrupt sources can be used to assert any
> combination of those 4 interrupt signals.
>
> What's wrong with using FIQs instead of IRQs for this purpose?
>
>> Is this what the MMP2_ICU_SP_IRQ_SEL/MMP2_ICU_PJ4_IRQ_SEL/MMP2_ICU_PJ4_FIQ_SEL
>> regs are for?
>
> Those registers are read-only; they *report* which one of the many
> hardware interrupts is currently selected for servicing, so that when an
> interrupt hits a CPU core it can discover which one to service.  (It's
> essentially a priority encoder/latch function.)
>
> The way you choose to route a given hardware interrupt to the 3 possible
> AP (PJ4) lines is by ICU_REG(4 * interrupt_number).  Routing to the
> security processor is done differently.
>
> Setting 0x10 in the routing register for interrupt_number routes it to
> SP IRQ.  Setting 0x20 routes to PJ IRQ, setting 0x40 routes to PJ FIQ.
> The lower 4 bits (mask 0xf) of the routing register set the priority,
> from 0 (lowest) to 0xf (highest).  You also need to know the mapping
> from hardware interrupt sources to interrupt_number, 0 <= interrupt_number
> <= 63.  But there are more than 64 interrupt sources, so some are ORed --
> numbers 4,5,17,35,51,55 have secondary control and status registers so
> you can control the 2nd level muxing.
>
> The Linux macros that correspond to the above are:
>   * ICU_INT_CONF(n) -- the register for interrupt_number n
>   * ICU_INT_CONF_MASK -- the priority bits, and
>   * ICU_INT_CONF_{{AP,CP}_INT,IRQ} -- the routing bits
>
> (Make sure to ignore the Linux code for pxa168/pxa910 -- we're pxa688.)
>
> Hopefully that's enough to get you going, feel free to ask more specific
> questions.  Thanks!
>

Thank you for the clarification of the ICU registers. I was interested
if, while I am in FIQ mode,
it were possible to manually trigger a particular IRQ interrupt (by
writing some ICU reg, to make it look like a hw irq occured), so that
while exiting FIQ I would cause
that interrupt to be serviced. If these are the only registers
described in the TRM, then I would guess 'no'.

Thanks again,
A