According to the clic specification
(https://github.com/riscv/riscv-fast-interrupt), the mnxti register has
be written, in order to clear the pending bit for non-vectored
interrupts. For vectored interrupts, this is automatically done.
From the spec:
"If the pending interrupt is edge-triggered, hardware will automatically
clear the corresponding pending bit when the CSR instruction that
accesses xnxti includes a write."
I added a kconfig `RISCV_SOC_HAS_CUSTOM_IRQ_HANDLING` to allow custom
irq handling. If enabled, `__soc_handle_all_irqs` has to be implemented.
For clic, non-vectored mode, I added a `__soc_handle_all_irqs`, that
handles the pending interrupts according to the pseudo code in the spec.
Signed-off-by: Greter Raffael <rgreter@baumer.com>
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