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device: 0.832
graphic: 0.731
other: 0.490
performance: 0.485
semantic: 0.482
vnc: 0.357
PID: 0.285
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debug: 0.269
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KVM: 0.013
Opentitan Timer ignores COMPARE_UPPER0/COMPARE_LOWER0
Description of problem:
In a bare metal application, running on an emulated Opentitan board, if you set a timer interrupt threshold by writing to `rv_timer.COMPARE_UPPER0` and `rv_timer.COMPARE_LOWER0` before writing to `rv_timer.CTRL` to start the timer, then the interrupt does not fire. If you write to the `COMPARE_*` registers *after* starting the timer by writing to `CTRL`, then the interrupt fires correctly.
I think the explanation is that [ibex_timer_update_irqs](https://gitlab.com/qemu-project/qemu/-/blob/master/hw/timer/ibex_timer.c?ref_type=heads#L61) has an early return if `rv_timer.CTRL` is not set. As a result, although writes to `COMPARE_*` always call `ibex_timer_update_irqs`, they don't have their intended side-effects before `CTRL` is unset.
Steps to reproduce:
Write to `rv_timer.COMPARE_UPPER0` and `rv_timer.COMPARE_LOWER0` before you have set `rv_timer.CTRL`. Observe that no timer interrupt occurs.
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