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** Changed in: qemu
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1850378
Title:
RISC-V unreliable IPIs
Status in QEMU:
Incomplete
Bug description:
I am working on a project with custom inter processor interrupts (IPIs) on
the RISC-V virt machine.
After upgrading from version 3.1.0 to 4.1.0 which fixes a related issue
(https://github.com/riscv/riscv-qemu/issues/132) I am able to use the CPU
hotplug feature.
However, if I try to use IPIs for communication between two cores, the
wfi instruction behaves strangely. Either it does not return, or it
returns on timer interrupts, even though they are disabled. The code,
I use on one core to wait for an interrupt is the following.
csr_clear(sie, SIE_SEIE | SIE_STIE);
do {
wait_for_interrupt();
sipval = csr_read(sip);
sieval = csr_read(sie);
scauseval = csr_read(scause) & 0xFF;
/* only break if wfi returns for an software interrupt */
} while ((sipval & sieval) == 0 && scauseval != 1);
csr_set(sie, SIE_SEIE | SIE_STIE);
Since the resulting sequence does not seem to be deterministic, my
guess is, that it has something to do with the communication of qemu's
threads for the different cores.
Update:
The exact same setup works fine in spike (the actual sim, not the qemu
board), which might give a hint, that it is related to the interrupt controller
implementation.
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