CONFIG_ZERO_LATENCY_IRQS and kernel services

[Hiihtaja]

Hello !

I can use ZERO latency IRQ with both methods of define interrupts :

IRQ_DIRECT_CONNECT(TIMER2_IRQn, CONFIG_TIMER_IRQ_PRIORITY,

timer2_isr_wrapper,

IS_ENABLED(CONFIG_ZERO_LATENCY_IRQS) ?

IRQ_ZERO_LATENCY : 0);

 

or 

IRQ_CONNECT(TIMER2_IRQn, CONFIG_TIMER_IRQ_PRIORITY, TIMER2_IRQHandler, NULL,

IS_ENABLED(CONFIG_ZERO_LATENCY_IRQS) ? IRQ_ZERO_LATENCY : 0);

And it is mentioned that not all services can be used in ISR :

"
Since Zero-latency ISRs will run in the same priority or possibly at
higher priority than the rest of the kernel they cannot use any
kernel functionality.
"

What services they talking about ?

Can I use k_sem_give() for example ?

I can see all ZERO latency interrupts have priority 0.

I have try to define CONFIG_ZERO_LATENCY_LEVELS=2 or 3 but there some compilation errors.


Regards,
Eugene

[Sigurd]

Hi,

"
Since Zero-latency ISRs will run in the same priority or possibly at higher priority than the rest of the kernel they cannot use any kernel functionality.
"

Here is a list over kernel serices, https://docs.zephyrproject.org/3.1.0/kernel/services/index.html

semaphores, and the use of k_sem_give() is a kernel service.

[Hiihtaja]

Hi Sigurd !

So I can think like this

IRQ_DIRECT_CONNECT have better latency than IRQ_CONNECT and adding IRQ_ZERO_LATENCY improve both ways of interrupt registration. But in case of IRQ_ZERO_LATENCY flag I can't use semaphores and other kernel services.

I hope I can use in any ZERO_LATENCY ISR APIs for manipulate with other ZERO_LATENCY ISR.

irq_disable()/irq_enable();

nrf_radio_int_disable(NRF_RADIO, ~((uint32_t)0));

NRFX_IRQ_PENDING_CLEAR(RADIO_IRQn);

May be I can schedule/trigger other interrupt ( like SW one) if I need to force some thread to run.

Or what is common technique for workaround in case of semaphore usage from Zero interrupts ?

Regards,

Eugene

[Sigurd]

Hi,

Looks like you can have multiple zero latency interrupt priorities.

See these PRs,

https://github.com/zephyrproject-rtos/zephyr/issues/45276

https://github.com/zephyrproject-rtos/zephyr/pull/45277

[Hiihtaja]

Hi Sigurd !

Yes you can 

But if you set 

CONFIG_ZERO_LATENCY_LEVELS=2 or 3,

some gpio component complain about build error.

Most probably not all components are updated.

And only ztest

/home/user/ncs/v2.3.0/zephyr/tests/arch/arm/arm_irq_zero_latency_levels/prj.conf

try to use it, others stay with defaults.

CONFIG_ZERO_LATENCY_IRQS=y
CONFIG_ZERO_LATENCY_LEVELS=2

you will see

from /home/user/ncs/v2.3.0/zephyr/drivers/gpio/gpio_nrfx.c:8:
/home/user/ncs/v2.3.0/zephyr/drivers/gpio/gpio_nrfx.c: In function 'gpio_nrfx_init':
/home/user/ncs/v2.3.0/zephyr/include/zephyr/toolchain/gcc.h:78:36: error: static assertion failed: "Invalid interrupt priority. Values must not exceed IRQ_PRIO_LOWEST"
78 | #define BUILD_ASSERT(EXPR, MSG...) _Static_assert(EXPR, "" MSG)
| ^~~~~~~~~~~~~~
/home/user/ncs/v2.3.0/zephyr/include/zephyr/arch/arm/aarch32/irq.h:105:9: note: in expansion of macro 'BUILD_ASSERT'
105 | BUILD_ASSERT(((flags_p & IRQ_ZERO_LATENCY) && \
| ^~~~~~~~~~~~
/home/user/ncs/v2.3.0/zephyr/include/zephyr/arch/arm/aarch32/irq.h:128:9: note: in expansion of macro '_CHECK_PRIO'
128 | _CHECK_PRIO(priority_p, flags_p) \
| ^~~~~~~~~~~
/home/user/ncs/v2.3.0/zephyr/include/zephyr/irq.h:49:9: note: in expansion of macro 'ARCH_IRQ_CONNECT'
49 | ARCH_IRQ_CONNECT(irq_p, priority_p, isr_p, isr_param_p, flags_p)
| ^~~~~~~~~~~~~~~~
/home/user/ncs/v2.3.0/zephyr/drivers/gpio/gpio_nrfx.c:378:9: note: in expansion of macro 'IRQ_CONNECT'
378 | IRQ_CONNECT(DT_IRQN(GPIOTE_NODE), DT_IRQ(GPIOTE_NODE, priority),
| ^~~~~~~~~~~
[127/192] Building C object zephyr/drivers/mbox/CMakeFiles/drivers__mbox.dir/mbox_nrfx_ipc.c.obj
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: /home/user/ncs/toolchains/v2.3.0/usr/local/bin/cmake --build /home/user/nsctest/timeslot/build

br, Eugene

[Sigurd]

Hi,

You might need to increase it further, try e.g. 10