The ARC IoT SoC (used on iotdk board) has a hardware limitation where
entering CPU sleep mode causes some peripherals (e.g., UART) to lose
power, preventing the board from waking up via peripheral interrupts.
Add a configurable custom CPU idle option (CONFIG_ARC_IOT_CUSTOM_CPU_IDLE)
that enables interrupts without executing the sleep instruction. This
allows the system to remain responsive while keeping peripherals powered.
The option defaults to disabled (n) to preserve normal CPU sleep behavior
for most use cases. Tests that require continuous UART operation during
idle (pytest/shell harnesses) can enable it via platform-specific
extra_configs.
This approach allows timer-based idle to work correctly by default while
providing a workaround for tests that need UART retention.
Signed-off-by: Mohamed Moawad <moawad@synopsys.com>
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