Hi, we are using as user level timer driver the PIT on Genode/seL4 and experience situations that the driver does not get IRQs after a while. It happens on Qemu as also on native x86 hardware.
We tracked down the problem to the masking of edge-triggered IRQs on the I/O APIC in the seL4 kernel. According to Intel, [0] chapter 3.2.4 "Interrupt Mask R/W", edge interrupts on a masked interrupt pin gets ignored and are not held pending. On [2] there are also some discussion about this topic too. We solved/workaround the issue by this patch [1]. I looked additionally into two other microkernels using the I/O APIC and they don't mask edge level triggered I/O APIC interrupts. I wonder if anybody already stumbled about the issue on seL4/x86? If not, please take the patch or give advices to adapt the patch so that it may get upstream. Thanks, Alexander Boettcher. [0] http://www.intel.com/design/chipsets/datashts/29056601.pdf [1] https://github.com/genodelabs/genode/blob/master/repos/base-sel4/patches/ioapic.patch [2] http://yarchive.net/comp/linux/edge_triggered_interrupts.html _______________________________________________ Devel mailing list [email protected] https://sel4.systems/lists/listinfo/devel
